Cryogenian
| Supereon | Eon | Era | Period | Start Million years ago |
|---|---|---|---|---|
| Phanerozoic | Palaeozoic | Cambrian | 0541 | |
| Precambrian | Proterozoic | Neoproterozoic | Ediacaran | 0635 |
| Cryogenian | 0850 | |||
| Tonian | 1000 | |||
| Mesoproterozoic | 1600 | |||
| Palaeoproterozoic | 2500 | |||
| Archaean | 4000 | |||
| Hadean | 4567 | |||
The Cryogenian is a geological period, from ~850 million years ago to 63 5mya.[1] It lies in the middle Proterozoic eon before the Ediacaran period.
The period is important to both Earth science and biology because it contains the two longest and most severe ice ages of all time:
- The Sturtian ice age 750 mya to 700 mya
- The Marinoan ice age 660 mya to 635 mya
These two snowball earth events were previously considered together as the Varangian glaciation. They covered much, possible all, the Earth with ice. The root cause of the temperature drop may have been the removal of CO2 from the atmosphere by photosynthesising bacteria and eukaryotes in the previous periods. Much else happened: the supercontinent Rodinia broke up and another, Pannotia, began to form. Fossil steroids suggest the presence of early sponges, and amoeboid cells with tests (coverings) appear in the fossil record.
References [change]
| Precambrian (4.567 gya – 541 mya) | |
|---|---|
| In the left column are Eons, bold are Eras, not bold are Periods. gya = billion years ago, mya = million years ago | |
| Hadean (4.567 gya – 4 gya) | |
| Archaean (4 gya – 2.5 gya) | |
| Proterozoic (4 gya – 2.5 gya) | Palaeoproterozoic (2.5 gya – 1.6 gya)
Mesoproterozoic (1.6 gya – 1 gya) Neoproterozoic (1 gya - 541 mya) Tonian (1 gya – 850 mya) Cryogenian (850 mya – 635 mya) Ediacaran (635 mya – 541 mya) |
| Source | International Chronostratigraphic Chart 2013. International Commission on Stratigraphy, retrieved 8 April 2013. Divisions of geologic time – major chronostratigraphic and geochronologic units USGS, retrieved 8 April 2013. |
