The first microorganisms on Earth are believed to have been
The first microorganisms on Earth are believed to have been simple single-celled organisms, similar to modern bacteria and archaea. Scientists estimate that they appeared about 3.5–4.0 billion years ago, not long after the Earth formed.
These early microbes lived in the oceans and obtained energy from chemicals in their environment because there was little or no oxygen in the atmosphere. Much later, a group of microorganisms called cyanobacteria evolved and began using sunlight to produce energy through photosynthesis. As a byproduct, they released oxygen, gradually transforming Earth’s atmosphere in an event known as the Great Oxidation Event.
The exact first species is unknown because no direct fossils of the very first life forms have been found. However, the earliest known life was likely a very simple microorganism that lived billions of years before plants, animals, or humans existed.
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