Mesoarchean

The Mesoarchean is a geologic era from a very long time ago, between 3,200 and 2,800 million years ago. It is part of the Archean Eon.

During this time, scientists found the first signs that Earth's plates were moving under each other. This process is called plate subduction. It was an important step in how our planet changed over millions of years.

This era also shows the first clear signs of tiny living things called microbes. These microbes were some of the earliest forms of life on Earth. The Mesoarchean is defined by measuring the exact age of rocks. This helps scientists understand the order of events in Earth's early history.

Tectonics

The Mesoarchean era is when modern-style plate movements may have started. We know this from the Pilbara Craton in western Australia. About 3.12 billion years ago, plates came together with a chain of islands. Later, around 2.97 billion years ago, two areas joined. A large group of landmasses called Vaalbara might have existed then.

Environmental conditions

By studying oxygen in special rocks called cherts, scientists have tried to learn about temperatures from long ago. These rocks suggest that ocean temperatures might have been between 55-85°C, but other studies suggest they were below 50°C.

The air during this time had lots of methane and carbon dioxide, which may help explain why it was warm. The amount of dinitrogen in the air was probably about the same as today, so nitrogen didn’t change Earth’s temperature much.

There was also a big cold period called the Pongola glaciation about 2.9 billion years ago, when ice reached places near the equator. This cold time probably didn’t happen because of new life forms that could make oxygen, which may have appeared later.

Early microbial life

During the Mesoarchean era, tiny life forms called microbes grew and changed. They made gases that changed the air around them on early Earth. One group of these microbes, called Cyanobacteria, made oxygen gas. But the oxygen did not stay in the air right away. Later, oxygen began to build up. Some shallow water near the shore had a bit more oxygen in it.