Paleoproterozoic

Paleoproterozoic Era 2500 - 1600 million years ago

Key events in the Paleoproterozoic view • discuss •  -2500 — – -2400 — – -2300 — – -2200 — – -2100 — – -2000 — – -1900 — – -1800 — – -1700 — – -1600 — – Neoarchean Mesoproterozoic Siderian Rhyacian Orosirian Statherian           P a l e o p r o t e r o z o i c  Proterozoic  Archean An approximate timescale of key Paleoproterozoic events. Axis scale: millions of years ago.

The Paleoproterozoic ( /ˌpeɪlɪ.oʊˌproʊtərɵˈzoʊ.ɨk/; also Palaeoproterozoic) is the first of the three sub-divisions (eras) of the Proterozoic occurring between 2,500 to 1,600 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.

Paleontological evidence on the Earth's rotational history suggests that ~1.8 billion years ago, there were about 450 days in a year, implying 20 hour days.

Paleoatmosphere

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 toxic to most anaerobic bacteria. It is widly believed that the majority of existent anaerobic life on Earth died off. 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.

Lifeforms

The crown eukaryotes, from which all modern day eukaryotic lineages have arisen have been dated to the paleoproterozoic era. By ~1 Gy the latest common ancestors between the ciliate and flagellate lineages probably diverged. The Francevillian Group and Grypania fossils and the first eukaryotes also appeared during this time.

Geological events

During this era the earliest global-scale continent-continent collisional belts developed.

These continent and mountain building events are represented by the 2.1-2.0 Ga (Ga = billion year) Transamazonian and Eburnean Orogens 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 collisional belts are interpreted as having resulted from 2.0-1.8 Ga global-scale collisional events that led to the assembly of a Paleo-Mesoproterozoic supercontinent named "Columbia" or "Nuna".

See also

(Impact events)

• Suavjärvi crater 2.4 billion years old
• Vredefort crater 2.023 ± .004 billion years old
• Sudbury Basin 1.849 billion years old

External links

• EssayWeb Paleoproterozoic Era
• 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].

Preceded by Archean Eon	2.5 Ga - Proterozoic Eon - 542 Ma										Followed by Phanerozoic Eon
	2.5 Ga - Paleoproterozoic Era - 1.6 Ga				1.6 Ga - Mesoproterozoic Era - 1.0 Ga			1.0 Ga - Neoproterozoic Era - 542 Ma
	Siderian	Rhyacian	Orosirian	Statherian	Calymmian	Ectasian	Stenian	Tonian	Cryogenian	Ediacaran