Living cells, like computers, store information, and it is estimated that they have been evolving and diversifying for more than 3.5 billion years. One might not expect that they would all store their information in the same form or that the hereditary information carried by one type of cell should be readable by the information-handling machinery of another. And yet it is so. This fact provides compelling evidence that all living things on Earth have inherited the form of their genetic instructions, as well as how to use them, from a universal common ancestral cell. This ancestor is thought to have existed roughly 3.5–3.8 billion years ago.
