While the first animals may have appeared around 800 million years ago, the first form of life on Earth is a whole lot older.
If we take Earth’s 4.5 billion year history and cram it into a single, 24-hour day, then the first animals would have emerged just after 8 o’clock in the evening. In this particular analogy, multicellular life appeared at 4 o’clock in the afternoon, eukaryotes (organisms whose cells have a membrane-bound nucleus) a little after midday, and prokaryotes (single-celled organisms whose cell lacks a nucleus) at 3 o’clock in the morning.
The last universal common ancestor of the three major domains of life – bacteria, archaea, and eukarya – lived even earlier, before 3 o’clock in the morning, or 4 billion years ago. This speck of life is known as LUCA and while it may be more than 4 billion years old, it’s still not the first form of life on Earth.
That particular title goes to the First Universal Common Ancestor (FUCA). There’s no evidence of FUCA in the fossil record and it’s more of a hypothesis than a single, definable organism, yet it’s widely cited as the first form of life on Earth. The exact timing of its origin is a mystery, but it likely appeared a short time after the Earth formed 4.5 billion years ago.
We’ve come a long way since FUCA, but at the end of the day our bodies – and those of other animals – are made up of the same fundamental building blocks. These building blocks are what creates life and what will continue to create new life far into the future, long after we’re gone.
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