Stenian

The Stenian Period (/ˈstiːni.ən/ STEE-nee-ən, from Ancient Greek: στενός, romanized: stenós, meaning "narrow") is the last geologic period in the Mesoproterozoic Era. It lasted from 1200 Mya to 1000 Mya (million years ago). Because there are very few fossils from this time, scientists use special dating methods to learn about this period.

During the Stenian Period, a giant landmass called a supercontinent, named Rodinia, came together. This process began in the earlier Ectasian Period and finished during the Stenian. Rodinia stayed together into the next period, called the Tonian, before breaking apart later. At this time, Rodinia was surrounded by a large ocean known as the Mirovian. Many smaller seas that had formed when an earlier supercontinent called Columbia broke apart disappeared during this period.

History

Before the Stenian period was named in 1991, a different time called the Riphean age was used. This age was thought to be from 1600 to 600 million years ago. It was mainly used in Russia and textbooks around the world.

In 1991, a scientist named K.A. Plumb introduced the Stenian period. He defined it as lasting from 1200 to 1000 million years ago. The name Stenian comes from the Ancient Greek word στενός, meaning "narrow." This name refers to the narrow belts of rocks formed during this time.

Geography

Most ideas about how the landmass named Rodinia looked show Laurentia in the middle. Other large land areas were around it. These areas include the East European Craton to the southeast, Amazonia to the south, and others such as Siberia, North, and South China cratons. The whole landmass was surrounded by a huge ocean called Mirovia.

Geology

This period brought big changes to Earth. The Keweenawan Rift formed, creating the Keweenawan Supergroup. The Musgrave orogeny happened, forming the Musgrave Block and the Warakurna Large igneous province.

Many events that built mountains occurred during this time. The Grenville orogeny was a major event. Other events like the Kibaran orogeny, the Dalslandian orogeny, and the Sunsás orogeny also happened. These events helped shape the supercontinent Rodinia.

Biology

Fossils of the oldest known organism that reproduced by having males and females, Bangiomorpha pubescens, appeared in the Stenian Period at the Hunting Formation in Somerset Island around 1.047 Bya. This period also marks the first known preserved case of life made of many cells in green algae, with Proterocladus antiquus dating back roughly 1 billion years ago.

Acritarchs became more common and developed spiny shapes during this time, likely due to increased competition among tiny, complex life forms. Stromatolites, which are layered structures made by ancient bacteria, reached their highest variety in this period but quickly decreased near its end around 1 billion years ago. By this time, complex cells called eukaryotes had become the main life forms in areas that were not oceans.

Climate

During the Stenian Period, the Sun shone with less brightness than it does today. Carbon dioxide in the air was higher than before the industrial era. Oxygen levels were low, only a small part of what we have now. There were no big ice ages, and each day lasted about 19 hours.