Mesoarchean

The Mesoarchean is a geologic era that happened a very long time ago, between 3,200 and 2,800 million years ago. It is part of something called the Archean Eon. During this time, scientists found the first signs that the Earth's plates were moving under each other in a process called plate subduction. This was an important step in how our planet has changed over millions of years.

This era also shows the first clear signs of tiny living things called microbes growing and spreading more widely. These microbes were some of the earliest forms of life on Earth. The Mesoarchean is defined by measuring the exact age of rocks, rather than by looking at layers of rock in one place. This helps scientists understand the order of events in Earth's very early history.

Tectonics

The Mesoarchean era is believed to be when modern-style plate movements began, based on evidence from the Pilbara Craton in western Australia. A place where plates came together with a modern-style chain of islands existed between two areas of Pilbara around 3.12 billion years ago. Later, around 2.97 billion years ago, one area of Pilbara joined with another. A large group of landmasses called Vaalbara might have existed during this time.

Environmental conditions

By studying oxygen in special rocks called cherts from the Mesoarchean, scientists have tried to figure out what the temperatures were like long ago. These rocks suggest that ocean temperatures might have been between 55-85°C (131-185°F), but other studies suggest average temperatures were below 50°C (122°F).

The air during the Mesoarchean had lots of methane and carbon dioxide, which may help explain why it was so warm. The amount of dinitrogen in the air back then was probably about the same as it is today, meaning nitrogen didn’t have a big effect on Earth’s temperature at the time.

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

Early microbial life

During the Mesoarchean era, tiny life forms called microbes grew and changed in many ways. 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. Much later, oxygen began to build up. Even so, by this time, some small areas of shallow water near the shore had a bit more oxygen in them.