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a cell: an irregular gray blob with smaller light and dark blobs and lines inside it: like the first cells

A very simple cell (seen through a microscope) like the first cells

RNA and lipid membranes

Sometime around four billion or 3.5 billion years ago, lipid membranes and RNA or DNA got together. They formed the earliest living cells on Earth. Nobody understands exactly how this happened.

What’s a lipid membrane?
What’s RNA?
What was Earth like at that time?
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But somehow some RNA or DNA molecules, or both, got into the water that was inside the bubbles of lipid membranes. It probably happened accidentally at first. RNA and DNA molecules just happened to be in the water where a lipid membrane was forming. But being inside lipid membranes turned out to be helpful to the RNA and DNA molecules, because the lipid membranes protected the molecules from water currents and other things and helped keep the RNA and DNA from breaking apart. These were the first cells. That’s all a really simple cell is: a big RNA or DNA molecule floating in water, surrounded by a lipid membrane that keeps it safer.

Natural selection favors the first cells

So natural selection caused more of the RNA and DNA that was inside bubbles lasted, while more of the RNA and DNA that was outside bubbles broke up into smaller pieces. After a while most of the RNA and DNA that was left was inside lipid membrane bubbles – inside cells.

What is natural selection?

How these cells reproduced

Like the RNA and DNA that were inside them, these simple cells were able to reproduce themselves. One cell could become two new cells. The cell began by using RNA molecules to make a copy of the cell’s DNA. Then, with one copy of the DNA in each half of the cell, the cell’s membrane would pinch itself in the middle and split apart, making two new cells, each pretty much the same as the old cell (except if copying mistakes had happened during the copying of the DNA).

Did you find out what you wanted to know about the first cells? Let us know in the comments!

Learn by doing – looking at a cell
More about cells

Bibliography and further reading about cells:

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