Neoproterozoic

The Neoproterozoic is the last of the three geologic eras of the Proterozoic eon, lasting from 1 billion to 538.8 million years ago. It marks the final era of the Precambrian "supereon" and comes after the Mesoproterozoic era and before the Paleozoic era of the Phanerozoic eon. This era is divided into three periods: the Tonian, Cryogenian, and Ediacaran.

One of the most striking events during this time happened in the Cryogenian period, when the Earth experienced a severe glaciation. Huge ice sheets may have covered the planet all the way to the equator, creating what scientists call a "Snowball Earth" that lasted around 100 million years.

The Neoproterozoic also holds important clues about the early development of life. The earliest fossils of complex life appear in the Tonian period, including a primitive sponge called Otavia. In the Ediacaran period, we find the oldest evidence of animals, known as the Ediacaran biota, along with the first clear fossils of cnidarians and bilaterians.

Scientists also believe that the Neoproterozoic was a time when much of the Earth's continental crust was formed, especially during major mountain-building events like the Pan-African orogeny and the Grenville orogeny. This era helped shape the continents we see today and set the stage for the burst of life that followed in the Paleozoic era.

Geology

At the start of the Neoproterozoic, a huge landmass called Rodinia sat right over the equator. Soon after, Rodinia began to break apart into smaller pieces.

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

Subdivisions

The Neoproterozoic is divided into three periods: 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 are known differently. The Tonian and Cryogenian are called the Late Riphean, and 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 discovered fossils of multicellular animals before the start of the Cambrian Period. These fossils were found in many places, including South West Africa, South Australia, Russia, England, and Canada. Many of these early animals were soft-bodied and their connection to modern animals is unclear. Some may be ancestors of animals alive today, while others seem to be unique forms that do not match any known group.

In China, scientists found fossils in the Doushantuo Formation and the Huainan biota. These include tiny marine organisms and small worm-shaped creatures. While evidence suggests animals might have appeared even earlier, physical fossils from that time are rare.

Terminal period

Main article: Ediacaran

Different countries used different names for the last period of the Neoproterozoic Era. In 2004, scientists agreed 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 marked by changes in fossils, not just by counting years.