History of the Earth
From Palaeos
The history of the Earth is roughly 4.6 billon years long spanning from when the Earth formed from a protoplanetary disk to the present Holocene epoch which begun in 10000 B.C.E. with the extinction of the Pleistocene megafauna. The Earth and life throughout Earth history has been quite dynamic with four official eons recognized world wide by paleontologists and geologists – the Hadean, Archaean, Proterozoic and Phanerozoic. These eons will be discussed below. See their individual pages for more detailed information.
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[edit] Hadean
The Hadean is the earliest unit of Earth history spanning from 4.5 bya to 3.8 bya. In this era many significant developments happened such as the formation of the Earth about 4.4 bya and the Earth's oceans. This estimate is based on recent research on zircon crystals rather than older estimates which would put it at 4.1 bya.
The formation of the Moon occurred around 4.5 bya according to the giant impact theory. Also the great heavy bombardment which impacted the Earth, Venus, Mars and the Moon happened then and may account for the lack of a sufficient geological record from this time. The appearance of a self replicating molecule around 4 bya gave rise to the common ancestor of all lifeforms around 3.8 bya as shown in the Isua green stone belt which contains mass amounts of organic carbon.
[edit] Archaean
The Archaean is the next eon which begins around 3.8 bya and ends around 2.5 bya. In this eon continents and continental shelves and plates appear. The first supercontinent Vallbaria appeared around 3.6 bya. Life changed much during this time too with the first stromatolites appearing around 3.5 bya. Around 2.7 bya some varieties of bacteria evolved oxy-photosynthesis which caused a poisonous build up of oxygen that probably killed off many types of anaerobic bacteria. The last universal common ancestor of all 3 domains Archaea, Eubacteria and Eukaryota appeared in the Archaean around 3.5 bya .
[edit] Proterozoic
In the Proterozoic many more advancements occurred in the history of life such as the appearance of multicellular organisms around 1.2bya and the first animals around 600 ma (with the exceptions of possible worm burrows and imprints from China, Canada and India dating from 1 bya-750 ma). Eukaryotic cells appeared in this time as a result of symbiosis between bacteria around 2.0-1.6 bya. Although the first animals appeared in this time, they were to diversify at the begining of the Phanerozoic in the Cambrian explosion. A super content called Rodina assembled around 1.3 ma which encompassed most of the land masses on Earth, much like Pangaea did much later in the Permian period in the Phanerozoic eon.
[edit] Phanerozoic
The Phanerozoic eon is the time we live in now, roughly 542 ma-2006ce. In this time animals diversified in the Cambrian explosion about 542ma. Major events of the Phanerozoic are Listed below:
- Plants colonize land-474ma
- Tetrapods appear-365ma
- First forests-370ma
- Permian-Triassic extinction event-249 ma
- First dinosaurs-230ma
- First mammals-220ma
- KT event-65ma
- First primates-55ma
- First hominids-7ma
- First modern humans-200000bce
The Phanerozoic is divided in to these periods:
