|MadSci Network: Evolution|
Dear Leyla: You asked "Which specimen appeared first in the fossil record?", which I take to mean "What are the oldest known fossils?" The oldest fossils are one-celled microorganisms, probably bacteria, that are about 3.4 billion years old. There are chemical fossils, which are organic chemicals believed to come only from decay of living tissue, that are about the same age. A reasonable estimate for how long it might have taken the processes of evolution to produce organisms like those indicated by the oldest known fossils is about 400 million years. If we use this estimate, that places the origin of life at about 3.8 billion years. If you want to know more about evidence for the origin of life on earth, here are some references that might be helpful: A. Lee McAlester, 1968, The History of Life: Englewood Cliffs, Prentice-Hall, Inc., 152 p. This little book is now a bit out of date but it is very well written and concise. L. E. Orgel, 1973, The origins of life: New York, John Wiley & Sons, 237 p. This book is a bit more advanced, but it is also slightly newer. Andre de Cayeux, 1964 (translated from the French, 1969), Three billion years of life: New York, Stein and Day, 239 p. Another old book, but very well written. R. H. Dott, Jr., and R. L. Batten, 1988, Evolution of the Earth, 4th edition, New York, McGraw-Hill, 643 p. This is actually a geology textbook, but has a good, up-to-date summary of the origin of life. M. F. Glaessner, 1984, The dawn of animal life, Cambridge (UK), Cambridge University Press, 244 p. This is one of the best books on the subject, and is still relatively up-to-date. For the latest word, you should search the indices of the journals Nature and Science. Most new discoveries in this field are published in one of those two most-prestigious journals. I hope this helps. David Kopaska-Merkel Geological Survey of Alabama PO Box 869999 Tuscaloosa AL 35486-6999 USA (205) 349-2852 FAX (205) 349-2861 web site www.gsa.state.al.us
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