Before the enormous increase in atmospheric oxygen, almost all existing lifeforms were Anaerobic_organism, i.e., their metabolism was based upon a form of cellular respiration that did not require oxygen. Indeed, 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. 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 (an event called, among numerous other similarly suggestive titles, the Oxygen Holocaust or Oxygen Catastrophe) is widely considered to be the first of the 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)—or the divergences that imply them between various groups of eukaryotes—have been ostensibly dated to around the time of the Paleoproterozoic era. However, these conclusions (as is the case in virtually any contemporaneously "hot" areas of biological study and research) are likely to be readjusted—if not outright abandoned—as more data become available, and should not be considered conclusive proof by any means. Nevertheless, given the number of and the peer respect assigned to many of the authors of these studies (and related analyses corroborating the validity of the methodologies used by those studies ...even though those very analyses are themselves also sometimes called into question), the final revisions will likely place the emergence of the oldest eukaryotic divergences around this period of time.
During this era, the earliest global-scale continent-continent collision belts developed.
These continent and mountain building events are represented by the 2.1–2.0 Ga Trans-Amazonian and Eburneanorogens in South America and West Africa; the ~2.0 Ga Limpopo Belt in southern Africa; the 1.9–1.8 Ga Trans-Hudson, Penokean, Taltson–Thelon, Wopmay, Ungava and Torngat orogens in North America, the 1.9–1.8 Ga Nagssugtoqidain Orogen in Greenland; the 1.9–1.8 Ga Kola–Karelia, Svecofennian, Volhyn-Central Russian, and Pachelma orogens in Baltica (Eastern Europe); the 1.9–1.8 Ga Akitkan Orogen in Siberia; the ~1.95 Ga Khondalite Belt and ~1.85 Ga Trans-North China Orogen in North China.
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.