The first living things on Earth were one-celled organisms, known as prokaryotes, that came into existence between about 3.5 and 4.1 billion years ago.

Prokaryotes do not have a cell nucleus.

Cells with nuclei are known as eukaryotic cells, and organisms that have such cells, including human beings, are knows as eukaryotes.

When the Earth was first formed, it was extremely hot.
Eventually, it cooled enough for the crust to solidify. Volcanoes formed, pouring ammonia, methane, nitrogen and carbon dioxide into the atmosphere.

Organic molecules coalesced in the oceans to form these molecules, and eventually formed prokaryotic cells.

When the first prokaryotes lived, there was almost no free oxygen in the air. Therefore, they were anaerobic (didn't breathe oxygen).

They probably ingested amino acids and excreted carbon dioxide and methane.

There are two types of prokaryotes - bacteria and archaea.

Archaea may have been the earliest form of life on Earth.

They live in extreme environments such as hot springs and deep sea vents.

The conditions in these environments resemble conditions that existed early in the Earth's history.


Stromatolites are layered structures of sediments that form in shallow bodies of waters.

Most of them are formed when large mats of microorganisms, known as microbial mats, trap sedimentary grains together.

These microorganisms are usually cyanobacteria, a type of bacteria also known as blue-green algae. Cyanobacteria use the process of photosynthesis to obtain energy.

3.5 million year old fossils of cyanobacteria have been found in stromatolites in Australia.