Re: Which specimen first appeared in the fossil record?

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Prentice-Hall, Inc., 152 p. This little book is now a bit out of date but 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