ONCE upon a time, 3 billion years ago, there lived a single organism called LUCA. It was enormous: a mega-organism like none seen since, it filled the planet’s oceans before splitting into three and giving birth to the ancestors of all living things on Earth today. New Scientist
It would be hundreds of millions of years before LUCA – the Last Universal Common Ancestor – would split into three basic branches of life: single-celled bacteria and archaea, and the more complex eukaryotes that would give birth to animals and plants.
What kept LUCA together was that its cells were constantly swapping parts – the genes and proteins that kept the organism alive. But slowly some of the cells developed ways of producing everything they needed, causing LUCA to break apart into multiple organisms. This appears to have coincided with the appearance of oxygen in the atmosphere, around 2.9 billion years ago. Putting together all these changes, life on Earth would never be the same again. Nor as together.