Life’s development has been much harder to definitively trace than that of the universe. This is because biology’s countless combinations and permutations are exceedingly convoluted compared to the linearity of physics or the predictability of chemistry.
Experimental physics is often conducted by holding all variables constant, then determining the effects of changing just one. This procedure, together with the universe’s constraints (which limit the number of particles [such as protons or electrons] there are to investigate and the number of ways they can behave) has simplified the discovery of many of the universe’s secrets. Physicists now extrapolate with confidence from present to past, from past to future, and from here to the other side of the universe.
Chemistry is somewhat more complex than physics, because there are over a hundred chemical elements. This relatively large number means that millions of different combinations (as molecules and compounds) can exist. This complexity is being conquered, however, as demonstrated by the near-routine formulation of new and improved fabrics, explosives, alloys, drugs, plastics, and innumerable other products.
Progress in biology, on the other hand, has been considerably slower until just recently. Life’s ability to mutate and change over successive generations has meant that investigators cannot simply extrapolate backwards to determine what previously existed, nor look forward and predict what might result.
Most of our knowledge about life’s history has been obtained from fossils and preserved remnants of past life forms, but two factors greatly complicate the task. First, biotic matter provides food for other living things, so most of it never makes its way into the future to be studied. Second, the extensive (and ongoing) geophysical changes that the Earth has undergone during its more than four billion years of existence has left the story-telling remains of life’s progress fragmented and incomplete. However, enough evidence exists and has been found for scientists to trace life’s gross history on this planet. Moreover, each year new fossils and new facts (particularly genetic) about past and present inter- and intra-species relationships are discovered. These fill knowledge gaps and build confidence in the accuracy of what has already been deduced. What biologists now generally accept is related in the following pages.
- Possible Origins Of Life On Earth
- Development Of Life On Earth
- The Probability That Life Exists Elsewhere
- Intelligent Life