ARCHEAN LIFE

Archean Earth differed greatly from our modern Earth not only in tectonic activity but also with respect to atmosphere and obviously life forms. The Archean atmosphere was enriched in carbon oxides, water vapor, nitrous oxides, hydrogen sulfide, ammonia, methane and other noxious gases. Most notably, the Archean atmosphere was depleted in free oxygen.

The Archean is known as the "Age of Prokaryotes", the first documented forms of life. Prokaryotes are simple, single-celled organisms that lack a nucleus, mitochondria and organized cell function. Prokaryotes have a distinct advantage over other life forms in that they reproduce asexually, which although boring is quite effective. Why is this form of reproduction "boring"? A very good question. The primary answer is that asexual reproduction precludes new genetic input, resulting in the same old, same old. However, this type of reproduction allows for the duplication of great numbers of individuals in a cookie cutter fashion. Therein lies the advantage: quick and simple reproduction. Prokaryotes include bacteria and --most important in our story-- Cyanobacteria!

Why are Cyanobacteria important? Stromatolite forming cyanobacteria are among the earliest Earth dwellers dating back at least 3.5 Ga, discovered in the Warawoona Formation of the Northwest  Territories of Canada. 

 

2.2 Ga stromatolites from Michigan's Kona Dolomite. Image courtesy of the World Museum of Natural History at http://www.wmnh.com/wmel0000.htm

Through photosynthetic activity, cyanobackteria fundamentally altered the Archean atmosphere through the production of a valuable waste product--free oxygen! Amazingly, prokaryotes have changed little in the past 3.5 Ga. In fact, one can travel to Sharks Bay, Australia and meet modern cousins of Earth's earliest inhabitants.

 

Modern cyanobacteria Stromatolites, Australia. Photo courtesy Marjory Martin

Additional Reading:           

Archean Life:                                 http://www.ucmp.berkeley.edu/precambrian/archaean.html

Earliest Eurkaryotes:                     http://www.sciencemag.org/cgi/content/full/285/5430/1033

Source and importance of Oxgen:http://www.sciencemag.org/cgi/content/full/288/5466/658

 

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