Paleoproterozoic

The Paleoproterozoic (pronounced /ˌpeɪlɪ.oʊˌproʊtərɵˈzoʊ.ɨk/, also spelled Palaeoproterozoic) is the first of the three sub-divisions (eras) of the Proterozoic occurring between 1,600 to 2,500 million years ago. This is when the continents first stabilized. This is also when cyanobacteria evolved, a type of bacteria which uses the biochemical process of photosynthesis to produce energy and oxygen.

Before the significant increase in atmospheric oxygen almost all life that existed was anaerobic, that is, the metabolism of life depended on a form of cellular respiration that did not require oxygen. Free oxygen in large amounts is poisonous to most anaerobic bacteria, and at this time most life on Earth vanished. The only life that remained was either resistant to the oxidizing and poisonous effects of oxygen, or spent its life-cycle in an oxygen-free environment. This main event is called the oxygen catastrophe. Also the Francevillian Group and Grypania fossils and the first eukaryotes appeared during this time.

The crown eukaryotes, from which most (all?) modern day eukaryotic lineages have arisen, date back to the paleoproterozoic sub-division. Also, during this time (~1 bya), the latest common ancestors between the ciliate and chordate lineages probably diverged.

During this era the earliest surviving mountain belt appears, in the Wopmay Fault Zone of Canada (West of Hudson Bay, 2100-1800 million years ago).

External links

* GeoWhen Database
* First breath: Earth's billion-year struggle for oxygen New Scientist, #2746, 5 February 2010 by Nick Lane. Posits an earlier much longer snowball period, c2.4 - c2.0 Gya, triggered by the Great Oxygenation Event.
* The information on eukaryotic lineage diversification was gathered from a New York Times opinion blog by Olivia Judson. See the text here: [1].