Paleoproterozoic

Paleoproterozoic Era (pronunciation: /pælioʊˌproʊtərəˈzoʊɪk-/;) is the first of the three sub-divisions (eras) of the Proterozoic Eon spanning 2,500 to 1,600 million years ago (2.5–1.6 Ga). It was during this era that the continents first stabilized.

Paleontological evidence on the Earth's rotational rate gave 20 hour days ~1.8 billion years ago, implying 450 days in a year.

Before the significant increase in atmospheric oxygen almost all life that existed was , that is, the metabolism of life depended on a form of cellular respiration that did not require oxygen.

Free oxygen in large amounts is toxic to most anaerobic bacteria. It is widely believed that the majority of the anaerobic life on Earth died around this time. The only life that remained was either resistant to the oxidizing and poisonous effects of oxygen, or spent its life-cycle sequestered in an oxygen-free environment. The sudden development of free oxygen and the ensuing die off of the vulnerable life forms is an event called the oxygen catastrophe.

The crown eukaryotes, from which all modern-day eukaryotic lineages have arisen, have been dated to the Paleoproterozoic era. By ~1 Ga they probably diverged from their latest common ancestors into the ciliate and flagellate lineages. The Francevillian and Grypania fossils and the first eukaryotes also appeared during this time.

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