Regents Earth Science (High School)

This text was written to prepare students for the New York State Regents Earth Science exam. As such, it closely follows the New York State Standards for Mathematics, Science, and Technology.

Introductory Concepts

Observation and Inference

Observation basically means watching something and taking note of anything it does. For instance, you might observe a bird flying by watching it closely. To infer is to draw a conclusion based on what one already knows and on that alone. Suppose you see rain on your window - you can infer from that, quite trivially, that the sky is grey.

Density

The concept of density is fundamental to understanding many aspects of Earth Science. Density is a derived unit. That is, the density of a substance must be calculated (or derived) from other measurements. Density is calculated by using the mass (grams) and volume (mL or cm³) of a given sample. Mass is determined by using a balance and volume of a fluid or solid can be determined by using a graduated cylinder. In this course, the equation for density is shown on p. 1 of the Earth Science Reference Tables as:

D = m/v, in which D represents density; m represents mass; and v represents volume. Some of the other sciences and engineering disciplines make use of a slightly different form of the equation for density. Solutions to problems that require the use of the density equation should include the corresponding metric system (or SI)units.

Density is considered an intrinsic property. That is, the density of a material at a specific temperature and pressure remains the same regardless of the size of the sample being considered. Density may be useful in helping to identify specific materials such as minerals, or in helping interpret or predict the behaviors of materials as they interact with other materials, or are subjected to changes in temperature or pressure.

Percent Error

The concept of "percent error" is also known as "percent deviation from an accepted value", and the second term may be more helpful in understanding what is actually being determined in the equation used to calculate it. All equations that are given in the Earth Science Reference Tables are on page 1.

The equation is (|(Accepted Value-Measured Value)|/(Accepted Value))*100, sometimes written as:

|(Difference from Accepted Value)|/(Accepted Value)*100, or simply: (Difference from Accepted Value)/(Accepted Value)*100.

Because one has already multiplied by 100, the equation will yield a percentage value, so the appropriate unit of % should be shown in your calculated value. One could report the value as positive or negative, and this would give information about whether your measurement is "high" or "low", but usually the absolute value of the percent deviation is reported (the difference is converted to a positive number).

The concept of percent error or percent deviation relates to a measure used by some people in statistics in which you determine how close a value that is measured (or that is calculated from measurements) is to a value that is given as "known" or "accepted". Thus the term "error" sometimes leads to a sense of panic that something was done wrong if the percent deviation from the accepted value is high. It is possible to have very high percent deviations if the accepted value is a small number, even if your measured value is close to the accepted. It is also possible that the particular thing one is measuring (say the mass for a mineral sample) may have a density that is slightly different from what is "accepted" because it contains some "impurities" (variations in the elemental composition). If one calculates a high value for a percent deviation from an accepted value, just make sure that the calculation has been done correctly, but never change the values measured to lower this percentage as these are based on actual observations!

Sample Questions

Multiple Choice

Which of these represents the density of a metal block whose mass is 200 g and volume 150 cubic centimeters?

(A) 3 000 grams per cubic centimeter. (B) 50 grams per cubic centimeter. (C) 350 grams per cubic centimeter. (D) 1.3 grams per cubic centimeter.

Constructed Response

(D) 1.3 grams per cubic centimeter

Earth's Dimensions

Shape of the Earth

The Earth is an oblate spheroid. It bulges at the equator and is flattened at the poles.

Evidence of its spherical shape comes from photographs of the Earth from space, seeing the shadow of Earth during a lunar eclipse, and the fact that ships seem to sink as they move farther into sea. Also, the altitude of the star Polaris increases with latitude.

Evidence for the fact that it is oblate comes from photographs of the Earth from space and variations in gravity along the Earth's surface (stronger at the poles where flattened, weaker at the equator where bulging, also, gravity does not pull directly down). Also, the altitude of Polaris does not vary uniformly when increasing latitude.

The best model for the earth is a globe or a ball because Yunis says so though the Earth is oblate, it is only slightly so. On Regents exams, very often there is a question about the shape of the Earth and the answer is a ping pong ball because it is smooth and round.

Rocks and Minerals

Minerals

Minerals are naturally occurring, inorganic, crystalline solids.

Inorganic substances are those not formed by living things, and in the majority of cases, this is true of all minerals, though there are some notable exceptions. Inorganic molecules usually do not contain carbon as a component in their atomic structures, though again, there are some inorganic minerals that are exceptions to this general statement.

A substance is said to be crystalline if it has a regular, repeating atomic structure. Each mineral has a specific atomic structure and formula, such as is given on page 16 of the Earth Science Reference Tables. The individual molecule made by these atoms forms the most basic structure of that type of mineral, and then typically combines chemically with others of the same kind so that the mineral becomes larger. Mineral samples may be microscopic or extremely large, but all the crystals of a single type of mineral share common chemical and physical properties because they share the same chemical composition, types of chemical bonds, and positions of the individual atoms within each of the mineral's molecules. This fact, that a single mineral, whether large or small reacts similarly to chemical and physical tests is very useful in identification.

Minerals are solids. There is actually a group of substances known as crystalline liquids, but those do not fit into the definition needed for this course.

Difference Between Rocks and Minerals

Rocks - Any natural formed aggregate or mass of mineral matter constituting an essential and appreciable part of the Earth's crust (AGI).

Mineral - A naturally formed chemical element or compound having a definite range in chemical composition, and usually a characteristic crystal form (AGI).

Properties of Minerals

Hardness

The hardness of a mineral is measured in several relative scales that are determined by how readily one mineral scratches the surface of another. The Mohs scale of hardness has ten level. #1 Talc, #2 gypsum, #3 calcite...... up to #10 DIAMOND the hardest natural substance because of the internal arrangement of its carbon atoms and the atomic bond forces in its tetrahedral shape.

Streak

The streak of a mineral refers to the color of the powder left behind when the mineral is scratched across a very hard surface, usually an unglazed porcelain plate. Most streak plates are white, though a few may be dark colored. Since a streak plate has a hardness of about 7 on Moh's scale of hardness, minerals that scratch a streak plate will obviously leave no powder behind (other than that of the streak plate itself). Typically, we group minerals by the colors of the streaks they produce. Oddly, many metallic minerals that appear shiny when viewed in a larger sample leave a dark or colored line on a streak plate. Since very small quantities of an element may cause a mineral to take on different colors, but streak tends to stay more or less consistent, we sometimes say that the color of the powdered mineral, or streak, is a more accurate test for a mineral's identity than using the color alone.

Color

The color of a mineral is generally easily influenced by a number of factors such as very small quantities of impurities in the mineral's atomic structure. Weathering of a mineral's surface may also influence how the color appears, so color is generally not as reliable a way to identify a specific mineral as is using tests such as hardness, the way a mineral breaks, or even the streak (the color of the powdered mineral).

There are also many other optical properties besides color that minerals may posses that may be unique to particular minerals, or groups of minerals.

Cleavage and Fracture

The way a mineral breaks is controlled mostly by the internal arrangement of its molecules. Though all minerals are considered crystalline and therefore have a repeating pattern of atoms in their structures, sometimes the chemical bonds in these patterns allow a mineral to break along smooth planes. Other times an uneven surface is produced. Since the way a mineral breaks is an expression of the molecular pattern, we can use this visible feature to infer properties about the internal structure of the mineral. Further, how a mineral breaks is a characteristic identifying feature of specific minerals. Breaking minerals may produce surprising results since some minerals may produce smooth crystal shapes as they form, yet break unevenly.

When a mineral breaks along smooth planes it possesses the property called cleavage. Minerals may break along one direction of cleavage or several. When there is more than one direction of cleavage, we are also interested in knowing the angles created between different cleavage directions. A single cleavage direction is inferred to extend throughout the entire sample, so it is important to not confuse parallel sides of the same cleavage plane that occur on different sides of a mineral sample. An example would be a mineral such as halite, that breaks with 3 directions of cleavage each at a 90 degree angle to each other. This pattern of breaking will produce a mineral sample shape that tends to be cubic, but any two opposite sides of the cubic shape are actually in the same plane, so the six sides of the broken sample result from three directions of cleavage. It is fun to slowly break a mineral using a tool such as a bench vise and watch the cleavage planes develop as the stress is applied to the sample, though you should wear appropriate safety equipment because sometimes little chips of the sample tend to fly off unpredictably!

When a mineral breaks unevenly, and does not break along smooth planes, it is said to break with fracture. Sometimes the type of fracture is itself characteristic, such as with the mineral quartz. Quartz has what is known as conchoidal fracture. Its fractured surfaces look somewhat like broken glass (most glass is made from quartz), and the name conchoidal comes from the word "conch" (like the sea shell) because this type of fracture makes a shell-like depression in the mineral as it breaks.

Knowing how specific minerals break and whether they have a certain type of fracture or if they have one or several directions of cleavage is one of the ways to help identify minerals or predict the behaviors a certain mineral may exhibit if it were to break. Useful information on minerals related to cleavage and fracture is found on page 16 of the Earth Science Reference Tables.

Luster

Luster refers to the way that light reflects off the surface of a mineral sample, particularly a freshly broken or unweathered surface of the sample. The two major divisions in the classification we make are whether minerals have metallic or non-metallic luster. On page 16 of the Earth Science Reference Tables, the only common mineral listed that may have either metallic or non-metallic luster is hematite. Like all physical properties of minerals, the luster of a mineral is due to the particular aspects of its chemical composition and its atomic bonds.

Rocks

Sedimentary

Break down (erosion) of rock will yield smaller sized particles (sediments). As sediments are moved from one place to another by a transporting medium (either by wind or water) they are deposited in basins (loactions where deposition occurs). If a cementing material is introduced to these sediments then lithification (formation of rock) will result and the outcome will be a Sedimentary rock.

Among the common cementing material is calcium carbonate and silica.

Sedimentary rock = Erosion of rock + transport of sediments + lithification.

Size of particles of a sedimentary rock indicate the environment of deposition. Coarse grained particle sizes indicate a terrestrial (land) to shallow marine environment. The smaller the particle size indicates the more we move towards the deeper sea environment.

Common sedimentary rocks are sandstone, limestone, shale and siltstone.

Igneous

Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from either the Earth's mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. The word "igneous" is derived from the Latin ignis, meaning "fire".

Magma origination The Earth's crust is about 35 kilometers thick under the continents, but averages only some 7-10 kilometers beneath the oceans. The continental crust is composed primarily of crystalline basement; stable igneous and metamorphic rocks such as granulite, granite and various other intrusive rocks. Oceanic crust is composed primarily of basalt, gabbro and peridotite.

The crust floats on the asthenospheric mantle, which is convecting due to the forces of plate tectonics. The mantle, which extends to a depth of nearly 3,000 kilometers is the source of all magma. Most of the magma which forms igneous rocks is generated within the upper parts of the mantle at temperatures estimated between 600 to 1600 °C.

Melting of rocks requires temperature, water and pressure. The mantle is generally over 1000 to 1200 °c beneath the crust, at depths of between 7 and 70km. However, most magma is generated at depths of between 20 and 50 km. Melting begins because of upwelling of hot mantle from deeper portions of the earth, nearer the Planetary core; because of water driven off subducted oceanic crust at subduction zones (providing water to lower the melting point of the rocks) and because of decompression caused by rifting.

Melting of the continental crust occurs rarely because it is usually dry, and composed of minerals and rocks which are resistant to melting such as pyroxene granulite. However, addition of heat from the mantle or from mantle plumes, subduction related compression and burial as well as some rifting, can prompt the continental crust to melt.

As magma cools, minerals crystallize from the melt at different temperatures (fractional crystallization). There are relatively few minerals which are important in the formation of igneous rocks. This is because the magma from which the minerals crystallize is rich in only certain elements: silicon, oxygen, aluminum, sodium, potassium, calcium, iron, and magnesium. These are the elements which combine to form the silicate minerals, which account for over ninety percent of all igneous rocks.

Bowen's reaction series is important for understanding the idealized sequence of fractional crystallization of a magma.

Igneous rocks make up approximately ninety five percent of the upper part of the Earth's crust, but their great abundance is hidden on the Earth's surface by a relatively thin but widespread layer of sedimentary and metamorphic rocks.

Igneous rock are geologically important because:

their minerals and global chemistry gives information about the composition of the mantle, from where some igneous rocks are extracted, and the temperature and pressure conditions that allowed this extraction, and/or of other pre-existing rock that melted; their absolute ages can be obtained from various forms of radiometric dating and thus can be compared to adjacent geological strata, allowing a time sequence of events; their features are usually characteristic of a specific tectonic environment, allowing tectonic reconstitution (see plate tectonics); in some special circumstances they host important mineral deposits (ores): for example, tungsten, tin, and uranium, are commonly associated with granites.

Morphology and setting In terms of modes of occurrence, igneous rocks can be either intrusive (plutonic) or extrusive (volcanic).

Intrusive igneous rocks Intrusive igneous rocks are formed from magma that cools and solidifies within the earth. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained. The mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body and its relation to the other formations into which it intrudes. Typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. The extrusive types usually are called lavas.

The central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores (called batholiths) may occupy huge areas of the surface.

Coarse grained intrusive igneous rocks which form at depth within the earth are termed as abyssal; intrusive igneous rocks which form near the surface are termed hypabyssal.

Extrusive igneous rocks Extrusive igneous rocks are formed at the Earth's surface as a result of the melting of rocks within the mantle.

The melted rock, called magma rises due to contrasting density with the surrounding mantle. When it reaches the surface, magma extruded onto the surface either beneath water or air, is called lava. Eruptions of volcanoes under the air are termed sub-aerial whereas those occurring underneath the ocean are termed submarine. Black smokers and mid ocean ridge basalt are examples of submarine volcanic activity.

Magma which erupts from a volcano behaves according to its temperature and composition, which cause a highly different range of viscosity. High temperature magma, which is usually basaltic in composition, behaves in a manner similar to thick oil and, as it cools, treacle. This forms pahoehoe type lava. Intermediate composition magma such as andesite tends to form cinder cones of intermingled ash, tuff and lava, and may have viscosity similar to thick, cold molasses or even rubber when erupted. Felsic magma such as rhyolite is usually erupted at low temperature and is up to 10,000 times as viscous as basalt. These volcanoes rarely form lava flows, and usually erupt explosively.

Felsic and intermediate rocks which erupt at surface often do so violently, with explosions driven by release of gases such as carbon dioxide trapped in the magma. Such volcanic deposits are called pyroclastic deposits, and include tuff, agglomerate and ignimbrite. Fine volcanic ash is also erupted and forms ash tuff deposits which can often cover vast areas.

Because lava cools and crystallizes rapidly, it is fine grained. If the cooling has been so rapid as to prevent the formation of even small crystals the resulting rock may be a glass (such as the rock obsidian).

Because of this fine grained texture it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine grained extrusive igneous rocks can only be determined by examination of thin sections of the rock under a microscope, so only an approximate classification can usually be made in the field.

Classification Igneous rock are classified according to mode of occurrence, texture, chemical composition, and the geometry of the igneous body.

The classification of the many types of different igneous rocks can provide us with important information about the conditions under which they formed. Two important variables used for the classification of igneous rocks are particle size, which largely depends upon the cooling history, and the mineral composition of the rock. Feldspars, quartz, olivines, pyroxenes, amphiboles, and micas are all important minerals in the formation of igneous rocks, and they are basic to the classification of these rocks. All other minerals present are regarded as nonessential (called accessory minerals).

In a simplified classification, igneous rock types are separated on the basis of the type of feldspar present, the presence or absence of quartz, and in rocks with no feldspar or quartz, the type of iron or magnesium minerals present.

Igneous rocks which have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic. Generally speaking, phaneritic implies an intrusive origin; aphanitic an extrusive one.

The crystals embedded in fine grained igneous rocks are termed porphyritic. The porphyritic texture develops when some of the crystals grow to considerable size before the main mass of the magma consolidates into the finer grained uniform material.

Texture

Texture is an important criterion for the naming of volcanic rocks. The texture of volcanic rocks, including the size, shape, orientation, and distribution of grains and the intergrain relationships, will determine whether the rock is termed a tuff, a pyroclastic lava or a simple lava.

However, the texture is only a subordinate part of classifying volcanic rocks, as most often there needs to be chemical information gleaned from rocks with extremely fine-grained groundmass or which are airfall tuffs which may be formed from volcanic ash.

Textural criteria are less critical in classifying intrusive rocks where the majority of minerals will be visible to the naked eye or at least using a hand lens, magnifying glass or microscope. Plutonic rocks tend also to be less texturally varied and less prone to gaining structural fabrics. Textural terms can be used to differentiate different intrusive phases of large plutons, for instance porphyritic margins to large intrusive bodies, porphyry stocks and subvolcanic apophyses. Mineralogical classification is used most often to classify plutonic rocks and chemical classifications are preferred to classify volcanic rocks, with phenocryst species used as a prefix, eg; "olivine-bearing picrite" or "orthoclase-phyric rhyolite".

Chemical classification Igneous rocks can be classified according to chemical or mineralogical parameters:

Chemical - Total alkali - silica content (TAS diagram) for volcanic rock classification used when modal or mineralogic data is unavailable:

acid igneous rocks containing a high silica content, greater than 63% SiO2 (examples rhyolite and dacite) intermediate igneous rocks containing between 52 - 63% SiO₂ (example andesite) basic igneous rocks have low silica 45 - 52% and typically high iron - magnesium content (example basalt) ultrabasic igneous rocks with less than 45% silica. (examples picrite and komatiite) alkalic igneous rocks with 5 - 15% alkali (K₂O + Na₂O) content (examples phonolite and trachyte) Note: the acid-basic terminology is used more broadly in older geological literature. Chemical classification also extends to differentiating rocks which are chemically similar according to the TAS diagram, for instance;

Ultrapotassic; rocks containing molar K₂O/Na₂O >3

Peralkaline; rocks containing molar K₂O + Na₂O/ Al₂O₃ >1 Peraluminous; rocks containing molar K₂O + Na₂O/ Al₂O₃ <1

Mineralogical classification For volcanic rocks, mineralogy is important in classifying and naming lavas. The most important criteria is the phenocryst species, followed by the ground mass mineralogy. Often, where the groundmass is aphanitic, chemical classification must be used to properly identify a volcanic rock.

Mineralogical contents - felsic versus mafic

felsic rock, with predominance of quartz, alkali feldspar and/or feldspathoids: the felsic minerals; these rocks (e.g., granite) are usually light colored, and have low density. mafic rock, with predominance of mafic minerals pyroxenes, olivines and calcic plagioclase; these rocks (example, basalt) are usually dark colored, and have higher density than felsic rocks. ultramafic rock, with more than 90% of mafic minerals (e.g., dunite) For intrusive, plutonic and usually phaneritic igneous rocks where all minerals are visible at least via microscope, the mineralogy is used to classify the rock. This usually occurs on ternary diagrams, where the relative proportions of three minerals are used to classify the rock.

The following table is a simple subdivision of igneous rocks according both to their composition and mode of occurrence.

Mode of occurrence Acid Intermediate Basic Ultrabasic Intrusive Granite Diorite Gabbro Peridotite Extrusive Rhyolite Andesite Basalt Komatiite

Example of classification Granite is an igneous, intrusive rock (crystallized at depth), with felsic composition (rich in silica and with more than 10% of felsic minerals) and phaneritic, subeuhedral texture (minerals are visible for the unaided eye and some of them retain original crystallographic shapes). Granite is the most abundant intrusive rock that can be found in the continents.

Etymology Volcanic rocks are named after Vulcan, the Roman name for the god of fire. Intrusive rocks are also called plutonic rocks, named after Pluto, the Roman god of the underworld.

Metamorphic Rock is new rock that forms when existing rocks are changed by heat, pressure, or chemicals. Heat and pressure deep underground bake and squeeze sedimentary and igneous rocks. The minerals within the rocks change, often becoming harder. In this way they form new rocks called metamorphic rocks. After millions of years, the top layers of rocks closest to the earth's surface are worn away by weather, shifts in the earth's crust, oceans, and rivers and metamorphic rock can appear on the surface.

Dynamic Earth

Plate Tectonics

Plate tectonics (from the Greek word for "one who constructs and destroys", τεκτων, tekton) is a theory of geology developed to explain the phenomenon of continental drift and is currently the theory accepted by the vast majority of scientists working in this area. In the theory of plate tectonics the outermost part of the Earth's interior is made up of two layers: the lithosphere comprising (1) the crust, which has an elemental composition of: oxygen, 46.6%; silicon, 27.7%; aluminum, 8.1%; and iron, 5.0%; and (2) the solidified uppermost part of the mantle. Below the lithosphere lies the asthenosphere which comprises the inner viscous part of the mantle. The mantle makes up 84% of the earth's volume and can sometimes get as hot as 3700 °C. Over millions of years the mantle behaves like a superheated and extremely viscous liquid, but in response to sudden forces, such as earthquakes, it behaves like a rigid solid and can 'ring like a bell'.

The lithosphere essentially "floats" on the asthenosphere. The lithosphere is broken up into what are called tectonic plates. The ten major plates are: African, Antarctic, Australian, Eurasian, North American, South American, Pacific, Cocos, Nazca, and the Indian plates. These plates (and the more numerous minor plates) move in relation to one another at one of three types of plate boundaries: convergent, divergent, and transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries (most notably around the Pacific Ring of Fire).

Plate tectonic theory arose out of two separate geological observations: continental drift, noticed in the early 20th century, and seafloor spreading, noticed in the 1960s. The theory itself was developed during the late 1960s and has since almost universally been accepted by scientists and has revolutionized the earth sciences (akin in its unifying and explanatory power for diverse geological phenomena as the development of the periodic table was for chemistry, the discovery of the genetic code for biology, and quantum mechanics in physics).

The division of the Earth's interior into lithospheric and asthenospheric components is based on their mechanical differences. The lithosphere is cooler and more rigid, whilst the asthenosphere is hotter and mechanically weaker. This division should not be confused with the chemical subdivision of the Earth into (from innermost to outermost) core, mantle, and crust. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which float on the fluid-like (visco-elastic liquid) asthenosphere. The relative fluidity of the asthenosphere allows the tectonic plates to undergo motion in different directions.

One plate meets another along a plate boundary, and plate boundaries are commonly associated with geological events such as earthquakes and the creation of topographic features like mountains, volcanoes and oceanic trenches. The majority of the world's active volcanoes occur along plate boundaries, with the Pacific Plate's Ring of Fire being most active and famous. These boundaries are discussed in further detail below.

Tectonic plates can include continental crust or oceanic crust, and typically, a single plate carries both. For example, the African Plate includes the continent and parts of the floor of the Atlantic and Indian Oceans. The part of the tectonic plate which is common in all cases is the uppermost solid layer of the upper mantle which lays beneath both continental and oceanic crust and is considered, together with the crust, lithosphere.

The distinction between continental crust and oceanic crust is based on the density of constituent materials; oceanic crust is denser than continental crust owing to their different proportions of various elements, particularly, silicon. Oceanic crust has less silicon and more heavier elements ("mafic") than continental crust ("felsic").

As a result, oceanic crust generally lies below sea level (for example most of the Pacific Plate), while the continental crust projects above sea level.

There are three types of plate boundaries, characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are:

1. Transform boundaries occur where plates slide, or perhaps more accurately grind, past each other along transform faults. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer). 2. Divergent boundaries occur where two plates slide apart from each other. 3. Convergent boundaries (or active margins) occur where two plates slide towards each other commonly forming either a subduction zone (if one plate moves underneath the other) or an orogenic belt (if the two simply collide and compress). Plate boundary zones occur in more complex situations where three or more plates meet and exhibit a mixture of the above three boundary types.

Transform (conservative) boundaries

The left- or right-lateral motion of one plate against another along transform faults can cause highly visible surface effects. Because of friction, the plates cannot simply glide past each other. Rather, stress builds up in both plates and when it reaches a level that exceeds the slipping-point of rocks on either side of the transform-faults the accumulated potential energy is released as strain, or motion along the fault. The massive amounts of energy that are released are the cause of earthquakes, a common phenomenon along transform boundaries.

A good example of this type of plate boundary is the San Andreas Fault complex, which is found in the western coast of North America and is one part of a highly complex system of faults in this area. At this location, the Pacific and North American plates move relative to each other such that the Pacific plate is moving northwest with respect to North America. In 50 million years or so, the part of California that is west of the San Andreas Fault will be a separate island near the Alaska area.

It should be noted that the actual direction of movement of the plates which abut at a transform like the San Andreas Fault is often not the same as their relative motion at the fault. For instance, the North American Plate as measured by GPS is actually moving southwestward, nearly perpendicular to the Pacific Plate while the Pacific Plate is actually moving slightly more westward than its relative northwest motion along the San Andreas Fault. [1] The resultant compressive forces are taken up by thrust faulting in the larger fault zone, producing California's Coast Range. The conspicuous bend in these ranges (the Transverse Ranges) and the San Andreas Fault itself in Southern California is a possible result of crustal spreading in the Great Basin region superimposed on the overall movement of the North American Plate. There is speculation by some geologists that rifting may be developing in the Great Basin as the crust here is measurably thinning.

Divergent (constructive) boundaries

At divergent boundaries, two plates move apart from each other and the space that this creates is filled with new crustal material sourced from molten magma that forms below. The origin of new divergent boundaries at triple junctions is sometimes thought to be associated with the phenomenon known as hotspots. Here, exceedingly large convective cells bring very large quantities of hot asthenospheric material near the surface and the kinetic energy is thought to be sufficient to break apart the lithosphere. The hot spot which may have initiated the Mid-Atlantic Ridge system currently underlies Iceland which is widening at a rate of a few centimeters per century.

Divergent boundaries are typified in the oceanic lithosphere by the rifts of the oceanic ridge system, including the Mid-Atlantic Ridge and the East Pacific Rise, and in the continental lithosphere by rift valleys such as the famous East African Great Rift Valley. Divergent boundaries can create massive fault zones in the oceanic ridge system. Spreading is generally not uniform, so where spreading rates of adjacent ridge blocks are different massive transform faults occur. These are the fracture zones, many bearing names, that are a major source of submarine earthquakes. A sea floor map will show a rather strange pattern of blocky structures that are separated by linear features perpendicular to the ridge axis. If one views the sea floor between the fracture zones as conveyor belts carrying the ridge on each side of the rift away from the spreading center the action becomes clear. Crest depths of the old ridges, parallel to the current spreading center, will be older and deeper (due to thermal contraction and subsidence).

It is at mid-ocean ridges that one of the key pieces of evidence forcing acceptance of the sea-floor spreading hypothesis was found. Airborne geomagnetic surveys showed a strange pattern of symmetrical magnetic reversals on opposite sides of ridge centers. The pattern was far too regular to be coincidental as the widths of the opposing bands were too closely matched. Scientists had been studying polar reversals and the link was made. The magnetic banding directly corresponds with the Earth's polar reversals. This was confirmed by measuring the ages of the rocks within each band. The banding furnishes a map in time and space of both spreading rate and polar reversals.

There is at least one plate that has no creative ridge associated with it: the Caribbean Plate. The Caribbean Plate is generally believed to have originated at a now extinct ridge in the Pacific Ocean, yet it remains in motion according to GPS measurements. The complex tectonics of this region are the subject of ongoing research.

Convergent (destructive) boundaries

The nature of a convergent boundary depends on the type of lithosphere in the plates that are colliding. Where a dense oceanic plate collides with a less-dense continental plate, the oceanic plate is typically thrust underneath, forming a subduction zone. At the surface, the topographic expression is commonly an oceanic trench on the ocean side and a mountain range on the continental side. An example of a continental-oceanic subduction zone is the area along the western coast of South America where the oceanic Nazca Plate is being subducted beneath the continental South American Plate. As the subducting plate descends, its temperature rises driving off volatiles (most importantly water). As this water rises into the mantle of the overriding plate, it lowers its melting temperature, resulting in the formation of magma with large amounts of dissolved gases. This can erupt to the surface, forming long chains of volcanoes inland from the continental shelf and parallel to it. The continental spine of South America is dense with this type of volcano. In North America the Cascade mountain range, extending north from California's Sierra Nevada, is also of this type. Such volcanoes are characterized by alternating periods of quiet and episodic eruptions that start with explosive gas expulsion with fine particles of glassy volcanic ash and spongy cinders, followed by a rebuilding phase with hot magma. The entire Pacific ocean boundary is surrounded by long stretches of volcanoes and is known collectively as The Ring of Fire.

Where two continental plates collide the plates either crumple and compress or one plate burrows under or (potentially) overrides the other. Either action will create extensive mountain ranges. The most dramatic effect seen is where the northern margin of the Indian Plate is being thrust under a portion of the Eurasian plate, lifting it and creating the Himalayas and the Tibetan Plateau beyond. It has also caused parts of the Asian continent to deform westward and eastward on either side of the collision.

When two plates with oceanic crust converge they typically create an island arc as one plate is subducted below the other. The arc is formed from volcanics which erupt through the overriding plate as the descending plate melts below it. The arc shape occurs because of the spherical surface of the earth (nick the peel of an orange with a knife and note the arc formed by the straight-edge of the knife). A deep undersea trench is located in front of such arcs where the descending slab dips downward. Good examples of this type of plate convergence would be Japan and the Aleutian Islands in Alaska.

As noted above, the plates are able to move because of the relative weakness of the asthenosphere. Dissipation of heat from the mantle is acknowledged to be the source of energy driving plate tectonics. Three-dimensional imaging of the Earth's interior (seismic tomography), indicates that convection of some sort is occurring throughout the mantleTanimoto 2000. How this convection relates to the motion of the plates is a matter of ongoing study and discussion. Somehow, this energy must be translated to the lithosphere in order for tectonic plates to move. There are essentially two forces that could be accomplishing this: friction and gravity.

Friction Mantle drag Convection currents in the mantle are transmitted through the asthenosphere; motion is driven by friction between the asthenosphere and the lithosphere. Trench suction Local convection currents exert a downward frictional pull on plates in subduction zones at ocean trenches.

Gravity Ridge-push Plate motion is driven by the higher elevation of plates at mid-ocean ridges. Essentially stuff slides downhill. The higher elevation is caused by the relatively low density of hot material upwelling in the mantle. The real motion producing force is the upwelling and the energy source that runs it. This is a misnomer as nothing is pushing and tensional features are dominant along ridges. Also, it is difficult to explain continental break-up with this. Slab-pull Plate motion is driven by the weight of cold, dense plates sinking into the mantle at trenches. There is considerable evidence that convection is occurring in the mantle at some scale. The upwelling of material at mid-ocean ridges is almost certainly part of this convection. Some early models of plate tectonics envisioned the plates riding on top of convection cells like conveyor belts. However, most scientists working today believe that the asthenosphere is not strong enough to directly cause motion by friction. Slab pull is widely believed to be the strongest force directly operating on plates. Recent models indicate that trench suction plays an important role as well. However, it should be noted that the North American Plate, for instance, is nowhere being subducted, yet it is in motion. Likewise the African, Eurasian and Antarctic Plates. The over-all driving force for plate motion and its energy source are still debatable subjects of on-going research. Lunar drag In a study published in the January-February 2006 issue of the Geological Society of America's journal Bulletin, a team of Italian and U.S. scientists argue that a component of the westward motion of the world's tectonic plates is due to the tidal attraction of the moon. As the Earth spins eastward beneath the moon, they say, the moon's gravity ever so slightly pulls the Earth's surface layer back westward. It may also explain why Venus and Mars have no plate tectonics since Venus has no moon, and Mars' moons are too small to have significant tidal effects on Mars. [2] This is not a new argument, however. It was originally raised by the "father" of the plate tectonic hypothesis, Alfred Wegener. It was challenged by the physicist Harold Jeffreys who calculated that the magnitude of tidal friction required would have quickly brought the earth's rotation to a halt long ago. One might also note that many plates are actually moving north and eastward, not west.

Plate motion is measured directly with the Global positioning satellite system (GPS).

Continental drift For more details on this topic, see Continental drift. Continental drift was one of many ideas about tectonics proposed in the late 19th and early 20th centuries. The theory has been superseded by and the concepts and data have been incorporated within plate tectonics.

By 1915 Alfred Wegener was making serious arguments for the idea with the first edition of The Origin of Continents and Oceans. In that book he noted how the east coast of South America and the west coast of Africa looked as if they were once attached. Wegener wasn't the first to note this (Francis Bacon, Benjamin Franklin and Snider-Pellegrini preceded him), but he was the first to marshal significant fossil and paleo-topographical and climatological evidence to support this simple observation. However, his ideas were not taken seriously by many geologists, who pointed out that there was no apparent mechanism for continental drift. Specifically they did not see how continental rock could plow through the much denser rock that makes up oceanic crust.

In 1947, a team of scientists led by Maurice Ewing utilizing the Woods Hole Oceanographic Institution’s research vessel Atlantis and an array of instruments, confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath the layer of sediments consisted of basalt, not granite which was common on the continents. They also found that the oceanic crust was much thinner than continental crust. All these new findings raised important and intriguing questions. [3]

Beginning in the 1950s, scientists, using magnetic instruments (magnetometers) adapted from airborne devices developed during World War II to detect submarines, began recognizing odd magnetic variations across the ocean floor. This finding, though unexpected, was not entirely surprising because it was known that basalt -- the iron-rich, volcanic rock making up the ocean floor-- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. This distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these newly discovered magnetic variations provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials recorded the Earth's magnetic field at the time.

As more and more of the seafloor was mapped during the 1950s, the magnetic variations turned out not to be random or isolated occurrences, but instead revealed recognizable patterns. When these magnetic patterns were mapped over a wide region, the ocean floor showed a zebra-like pattern. Alternating stripes of magnetically different rock were laid out in rows on either side of the mid-ocean ridge: one stripe with normal polarity and the adjoining stripe with reversed polarity. The overall pattern, defined by these alternating bands of normally and reversely polarized rock, became known as magnetic striping.

When the rock strata of the tips of separate continents are very similar it suggests that these rocks were formed in the same way implying that they were joined initially. For instance, some parts of Scotland contain rocks very similar to those found in eastern North America. Furthermore, the Caledonian Mountains of Europe and parts of the Appalachian Mountains of North America are very similar in structure and lithology.

Floating continents The prevailing concept was that there were static shells of strata under the continents. It was early observed that although granite existed on continents, seafloor seemed to be composed of denser basalt. It was apparent that a layer of basalt underlies continental rocks.

However, based upon abnormalities in plumb line deflection by the Andes in Peru, Pierre Bouguer deduced that less-dense mountains must have a downward projection into the denser layer underneath. The concept that mountains had "roots" was confirmed by George B. Airy a hundred years later during study of Himalayan gravitation, and seismic studies detected corresponding density variations.

By the mid-1950s the question remained unresolved of whether mountain roots were clenched in surrounding basalt or were floating like an iceberg.

Plate tectonic theory Significant progress was made in the 1960s, and was prompted by a number of discoveries, most notably the Mid-Atlantic ridge. The most notable was the 1962 publication of a paper by American geologist Harry Hess (Robert S. Dietz published the same idea one year earlier in Nature. However, priority belongs to Hess, since he distributed an unpublished manuscript of his 1962 article already in 1960). Hess suggested that instead of continents moving through oceanic crust (as was suggested by continental drift) that an ocean basin and its adjoining continent moved together on the same crustal unit, or plate. In the same year, Robert R. Coats of the U.S. Geological Survey described the main features of island arc subduction in the Aleutian Islands. His paper, though little-noted (and even ridiculed) at the time, has since been called "seminal" and "prescient". In 1967, Jason Morgan proposed that the Earth's surface consists of 12 rigid plates that move relative to each other. Two months later, in 1968, Xavier Le Pichon published a complete model based on 6 major plates with their relative motions.

Explanation of magnetic striping

Seafloor magnetic striping.The discovery of magnetic striping and the stripes being symmetrical around the crests of the mid-ocean ridges suggested a relationship. In 1961, scientists began to theorise that mid-ocean ridges mark structurally weak zones where the ocean floor was being ripped in two lengthwise along the ridge crest. New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. This process, later called seafloor spreading, operating over many millions of years has built the 50,000 km-long system of mid-ocean ridges. This hypothesis was supported by several lines of evidence:

1. at or near the crest of the ridge, the rocks are very young, and they become progressively older away from the ridge crest; 2. the youngest rocks at the ridge crest always have present-day (normal) polarity; 3. stripes of rock parallel to the ridge crest alternated in magnetic polarity (normal-reversed-normal, etc.), suggesting that the Earth's magnetic field has flip-flopped many times.

By explaining both the zebra like magnetic striping and the construction of the mid-ocean ridge system, the seafloor spreading hypothesis quickly gained converts and represented another major advance in the development of the plate-tectonics theory. Furthermore, the oceanic crust now came to be appreciated as a natural "tape recording" of the history of the reversals in the Earth's magnetic field.

Subduction discovered A profound consequence of sea floor spreading is that new crust was, and is now, being continually created along the oceanic ridges. This idea found great favor with some scientists who claimed that the shifting of the continents can be simply explained by a large increase in size of the Earth since its formation. However, this so-called "Expanded earth theory" hypothesis was unsatisfactory because its supporters could offer no convincing geologic mechanism to produce such a huge, sudden expansion. Most geologists believe that the Earth has changed little, if at all, in size since its formation 4.6 billion years ago, raising a key question: how can new crust be continuously added along the oceanic ridges without increasing the size of the Earth?

This question particularly intrigued Harry Hess, a Princeton University geologist and a Naval Reserve Rear Admiral, and Robert S. Dietz, a scientist with the U.S. Coast and Geodetic Survey who first coined the term seafloor spreading. Dietz and Hess were among the small handful who really understood the broad implications of sea floor spreading. If the Earth's crust was expanding along the oceanic ridges, Hess reasoned, it must be shrinking elsewhere. He suggested that new oceanic crust continuously spread away from the ridges in a conveyor belt-like motion. Many millions of years later, the oceanic crust eventually descends into the oceanic trenches -- very deep, narrow canyons along the rim of the Pacific Ocean basin. According to Hess, the Atlantic Ocean was expanding while the Pacific Ocean was shrinking. As old oceanic crust was consumed in the trenches, new magma rose and erupted along the spreading ridges to form new crust. In effect, the ocean basins were perpetually being "recycled," with the creation of new crust and the destruction of old oceanic lithosphere occurring simultaneously. Thus, Hess' ideas neatly explained why the Earth does not get bigger with sea floor spreading, why there is so little sediment accumulation on the ocean floor, and why oceanic rocks are much younger than continental rocks.

Mapping with earthquakes During the 20th century, improvements in seismic instrumentation and greater use of earthquake-recording instruments (seismographs) worldwide enabled scientists to learn that earthquakes tend to be concentrated in certain areas, most notably along the oceanic trenches and spreading ridges. By the late 1920s, seismologists were beginning to identify several prominent earthquake zones parallel to the trenches that typically were inclined 40-60° from the horizontal and extended several hundred kilometers into the Earth. These zones later became known as Wadati-Benioff zones, or simply Benioff zones, in honor of the seismologists who first recognized them, Kiyoo Wadati of Japan and Hugo Benioff of the United States. The study of global seismicity greatly advanced in the 1960s with the establishment of the Worldwide Standardized Seismograph Network (WWSSN) to monitor the compliance of the 1963 treaty banning above-ground testing of nuclear weapons. The much-improved data from the WWSSN instruments allowed seismologists to map precisely the zones of earthquake concentration worldwide.

Geological paradigm shift The acceptance of the theories of continental drift and sea floor spreading (the two key elements of plate tectonics) can be compared to the Copernican revolution in astronomy (see Nicolaus Copernicus). Within a matter of only several years geophysics and geology in particular were revolutionized. The parallel is striking: just as pre-Copernican astronomy was highly descriptive but still unable to provide explanations for the motions of celestial objects, pre-tectonic plate geological theories described what was observed but struggled to provide any fundamental mechanisms. The problem lay in the question "How?". Before acceptance of plate tectonics, geology in particular was trapped in a "pre-Copernican" box.

However, by comparison to astronomy the geological revolution was much more sudden. What had been rejected for decades by any respectable scientific journal was eagerly accepted within a few short years in the 1960s and 1970s. Any geological description before this had been highly descriptive. All the rocks were described and assorted reasons, sometimes in excruciating detail, were given for why they were where they are. The descriptions are still valid. The reasons, however, today sound much like pre-Copernican astronomy.

One simply has to read the pre-plate descriptions of why the Alps or Himalaya exist to see the difference. In an attempt to answer "how" questions like "How can rocks that are clearly marine in origin exist thousands of meters above sea-level in the Dolomites?", or "How did the convex and concave margins of the Alpine chain form?", any true insight was hidden by complexity that boiled down to technical jargon without much fundamental insight as to the underlying mechanics.

With plate tectonics answers quickly fell into place or a path to the answer became clear. Collisions of converging plates had the force to lift sea floor into thin atmospheres. The cause of marine trenches oddly placed just off island arcs or continents and their associated volcanoes became clear when the processes of subduction at converging plates were understood.

Mysteries were no longer mysteries. Forests of complex and obtuse answers were swept away. Why were there striking parallels in the geology of parts of Africa and South America? Why did Africa and South America look strangely like two pieces that should fit to anyone having done a jigsaw puzzle? Look at some pre-tectonics explanations for complexity. For simplicity and one that explained a great deal more look at plate tectonics. A great rift, similar to the Great Rift Valley in north eastern Africa, had split apart a single continent, eventually forming the Atlantic Ocean, and the forces were still at work in the Mid-Atlantic Ridge.

We have inherited some of the old terminology, but the underlying concept is as radical and simple as "The Earth moves" was in astronomy.

Meteorology

Measuring Weather - Weather Variables

Temperature

A measurement of energy in a substance's molecules. More active molecules bump into each other and friction occurs and is therefore warm or hot. A cooler substance is less active and it's molecules don't rub together so less heat is given off. Temperature is measured in many units but most commonly degrees Celsius, degrees Fahrenheit, kelvin, or BTU. Temperature is measured using a thermometer.

Dewpoint

The temperature at which H₂O molecules in the air will condense.

Relative Humidity

The percentage of H₂O molecules in the air compared to the possible amount (absolute humidity). A hydrometer or hygrometer can be used to measure relative humidity. Multiple Choice

A student using a sling psychrometer measured a wet-bulb temperature of 10°C and a dry-bulb temperature of 16° What was the dewpoint? (1)10°C (3) 6°C (2)45°C (4) 4°C

Air Pressure

Air is made of molecules. Most of the air is made of nitrogen: N₂ (78%). There is also some oxygen: O₂ (21%) as well as small amounts of carbon dioxide: CO₂ and other gases. Air molecules are moving around very quickly. When air molecules hit a surface, they exert a force known as pressure.

Imagine that you are at the bottom of an ocean of air. The air pressure that you measure is caused by the weight of all of this air.

Pressure is measured using a barometer and labeled in millibars (mb).

Wind Speed

The velocity of wind gusts. Commonly measured in mph (miles per hour) or km/h (kilometers per hour). The tool used to measure wind speed is called an anemometer.

Wind Direction

The direction on a wind rose that the wind is blowing. The tool used to measure wind direction is a weather vane.

Extreme Weather

Thunderstorms

Probably the most common of storms, these form when large-scale convection occurs, drawing warm, moist air up into colder parts of the troposphere. This can happen along fronts, because of local topography such as mountains, and because of the rising of a warm air parcel over a piece of warm land. the moisture is converted into deep cumulus and cumulonimbus clouds, the warm air of which, becomes the updraft. As the air rises up high enough, perhaps even to the tropopause, it cools, and begins to sink, forming a downdraft.

This huge mixing of air molecules throws both water droplets, which nucleate to a small particles such as dust or pollen, as well as electrical charges all about the cloud. Remember that water molecules are polar, which means they have separated charges. This means that they carry electrical particles easily. The winds separate ice droplets and water droplets, the latter of which tends to carry a positive charge. Negative charges in the air and along the ground align with the cloud and travel with it. When they meet, as in a high point on a tree or cliff, an electrical discharge occurs, and lightning is born. The super-hot zap of energy quickly heats the immediate air surrounding it, creating a loud shock wave known as thunder.

The water droplets often coelace, forming bigger and bigger drops until they are heavy enough to fall as rain. If the droplets are carried up to the freezing point repeatedly, adding new water layers on each time until it too is heavy enough to fall, hail results.

Sample Questions

Multiple Choice

A student using a sling psychrometer measured a wet-bulb temperature of 10°C and a dry-bulb temperature of 16° What was the dewpoint? (1)10°C (3) 6°C (2)45°C (4) 4°C

Climate and Water Cycle

Hydrologic Cycle

Precipitation

Evaporation

Infiltration

Run off

Earth's History

Sample Questions

Question # 1

What is the Earth's shape most likely related to?

• a)pear
• b)oval
• c)ping-pong ball
• d)none of the above

The answer would be c)ping pong ball

Question # 2

A layer that is not folded, what layer is the oldest?

• a)the top layer
• b)the middle layer
• c)the bottom layer
• d)all of the layers are the same age

The answer would be c)the bottom layer

Constructed Response

3. How can we find the number of half-life that has passed?

Astronomy

Astronomy is the study of all matter and energy systems that exist outside, or "above", the region of the Earth's atmosphere. It also includes the histories and possible future behaviors of this matter and these energy systems. The Earth is derived from the matter and energy that surrounds it, and continues to be influenced by events in space.

Introduction to the Solar System and Planets

The solar system consists of the sun and anything that orbits it.

It has planets, which are spherical objects that orbit the sun and rotate on an axis. The planets are divided into terrestrial planets, which include Mercury, Venus, Earth, and Mars and are made of solids, and Jovian planets, which include Jupiter, Saturn, Uranus, and Neptune and are made of gases. Many planets have moons revolving around them.

Asteroids are mostly non-spherical objects that orbit the sun. They are found mostly in a belt between Mars and Jupiter.

Comets are objects made of ice, dust, and gas. They orbit the sun in a very elliptical shape. When they are close to the sun, they melt partially, which causes them to have a 'tail'.

Meteorites are small rock like substances orbiting the sun. When they enter Earth's atmosphere, they burn and are called meteors or shooting starts. If they hit the Earth, they can leave impact craters.

Patterns in Celestial Movements

The Sun's Daily Path

The sun moves from the east to the west. During the winter, it rises and sets due south of east and its apparent path is lower in the sky. During the Summer, it rises and sets due north of east and its apparent path is higher in the sky.

Earth's Revolution

Earth's orbit causes the seasons and takes approximately 365.25 days to complete.

The orbit is maintained by the balance of gravity, or the attractive force between to substances, and inertia. The shape of the orbit is slightly elliptical, with one of the foci being the sun. This causes the Earth to be closest to the sun in January and farthest from the sun in July with the apparent diameter of the sun being larger in July. It does not cause the seasons.

Sample Questions

Constructed Response

The answer would be, a ping pong ball

Environmental Awareness

Study Tips for the Regents Earth Science Exam

Understanding Relationships Between Variables

In science, we use either sentences or graphs to show how one thing affects another. For example, we can say that the more homework you do, the higher your grade will be.

Another way to say this is...

As the homework you do increases, your grade will also increase

Sentences that describe relationships often follow this format...

1.  They begin with the words, "As the"
2.  They include the first variable (in this case, "number of pieces of homework you do")
3.  The first variable is followed by the word, "increase(s)" or "decrease(s)"
4.  Then you put the second variable (in this case, "your grade".
5.  The second variable is followed by the word, "increase(s)" or "decrease(s)"

Using the directions above, create sentences that describe the relationships between the following...

• 1. The age and height of a child.
• 2. The time between meals and your hunger.

These relationships can also be represented as graphs.

External Links

• Earth Science Reference Tables
• Archive of Past Earth Science Regents Exams with Scoring Guides
• Resources to Assist Students with Special Needs
• The Physical Setting: Earth Science (Regents Earth Science) Core Curriculum
• An online version of the Regents Earth Science Core Curriculum - a resource that was primarily designed for teachers, but nonetheless forms the basis for the information in this text is also available.

Earth science is a lot of common sense thinking, for example if you think about it you could know it without being taught, it just makes sense. For example, if you are seeing which rock layer comes first and there is an intrusion, if you think about it the intrusion can't have come first because it had nothing to intrude so the rock layers had to lay down first