The Earth is 4.543 billion years old (!). The earliest known life forms appeared on Earth approximately 3.77 billion years ago.
These were micro-organisms.
Biologists believe that all cells had a common ancestor cell known as the Last Universal Common Ancestor (aka LUCA). This 2016 research paper theorizes that our ancestor LUCA probably lived in deep-sea hydrothermal vents.
Over time, LUCA and his sibling LUCA’s evolved into three different cell types, each then gained its own domain.
These three domains are the Bacteria, Archaea, and the Eukaryota.
Bacteria: are prokaryotic true bacteria that are common in our daily life – they live on our skin and in our guts. There are millions of bacterial cells in a handful of soil or a few drops of water. Bacteria (or eubacteria) have no nucleus. Unlike archaeabacteria though, they do not contain unused sections of genes.
Archaea: are prokaryotic primitive bacteria that usually live in extreme environments. They have no nucleus and contain unused sections of genes.
Eukaryota:
These are sub-divided into 4 kingdoms – protists, fungi, plants and animals. In other words, if you are reading this, you are eukaryotic! Yay, you!
Eukaryotes do have a nucleus but like archaea, also have unused sections of genes.
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