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First era of the Proterozoic Eon
Paleoproterozoic Era 2500-1600 million years ago
The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from 2,500 to 1,600million years ago (2.5-1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's geological history. It was during this era that the continents first stabilized.
Paleontological evidence suggests that the Earth's rotational rate during this era resulted in 20-hour days ~1.8 billion years ago, implying a total of ~450 days per year.
Before the enormous increase in atmospheric oxygen, almost all existing lifeforms were anaerobic organisms, whose metabolism was based upon a form of cellular respiration that did not require oxygen. Free oxygen in large amounts is toxic to most anaerobic organisms. Consequently, the majority of the anaerobic lifeforms on Earth died when the atmospheric free-oxygen levels soared in an extinction event called the Great Oxidation Event. The only lifeforms that survived were either those resistant to the oxidizing and poisonous effects of oxygen, or those sequestered in oxygen-free environments. The sudden increase of atmospheric free oxygen and the ensuing extinction of the vulnerable lifeforms is widely considered to be the one of the first and most significant mass extinctions in the history of the Earth.
Emergence of Eukarya
Many crown node eukaryotes (from which the modern-day eukaryotic lineages would have arisen) have been approximately dated to around the time of the Paleoproterozoic era.
While there is some debate as to the exact time at which eukaryotes evolved,
current understanding places it somewhere in this era.
These continental collision belts are interpreted as having resulted from one or more 2.0-1.8 Ga global-scale collision events that then led to the assembly of a Proterozoic supercontinent named Columbia or Nuna.