Neoproterozoic

The Neoproterozoic is the last of the three geologic eras of the Proterozoic eon. It lasted from 1 billion to 538.8 million years ago. This era marks the final part of the Precambrian and comes after the Mesoproterozoic and before the Paleozoic era of the Phanerozoic eon.

The Neoproterozoic is divided into three periods: the Tonian, Cryogenian, and Ediacaran.

During the Cryogenian period, the Earth went through a very cold time. Huge ice sheets may have covered the planet, even near the equator. Scientists call this time a "Snowball Earth."

The Neoproterozoic gives us important clues about early life. The first fossils of complex life appeared in the Tonian period. This includes a simple sponge called Otavia. In the Ediacaran period, we find the oldest signs of animals, called the Ediacaran biota. We also see the first clear fossils of cnidarians and bilaterians.

Scientists think that much of the Earth's continental crust formed during the Neoproterozoic. Big events like the Pan-African orogeny and the Grenville orogeny helped build the continents we know today. This era set the stage for the growth of life in the Paleozoic era that followed.

Geology

At the start of the Neoproterozoic, a large landmass called Rodinia was right over the equator. After that, Rodinia broke into smaller pieces.

Later, Earth had very cold times with big ice ages, including the Sturtian and Marinoan glaciations. These were so cold that ice might have covered Earth completely, in a state called the "Snowball Earth."

Subdivisions

The Neoproterozoic is divided into three periods. These are the Tonian from 1 billion to 720 million years ago, the Cryogenian from 720 million to 635 million years ago, and the Ediacaran from 635 million to 538.8 million years ago.

In Russia, these periods have different names. The Tonian and Cryogenian are called the Late Riphean. The Ediacaran is called the Early to middle Vendian. In Siberia, geologists use the names Mayanian for the time from 1 billion to 850 million years ago and Baikalian for the time from 850 million to 650 million years ago.

Paleobiology

Main article: Ediacaran biota

Scientists found fossils of animals with many cells before the start of the Cambrian Period. These fossils were found in South West Africa, South Australia, Russia, England, and Canada. Many of these early animals did not have hard parts and it is unclear how they are related to animals today. Some may be ancestors of animals we see now, while others are unique and do not match any known group.

In China, scientists found fossils in the Doushantuo Formation and the Huainan biota. These include tiny sea creatures and small worm-like animals. While it seems animals may have appeared even earlier, fossils from that time are very rare.

Terminal period

Main article: Ediacaran

Different places used different names for the last part of the Neoproterozoic Era. In 2004, scientists chose to call this time the Ediacaran Period. It lasted from 635 to 538.8 million years ago. The start and end of the Ediacaran are shown by changes in fossils, not just by counting years.