A brief History of Life on Earth

Life is valuable to all of us, but how it began is not something many people are interested in discussing. This is a brief summary of one version the history of life on Earth, agreed on by most biologists.
The Earth's crust formed about 4.5 billion years ago. There are various theories as to what it was that caused the first prokaryotic cells to form 700 million years later. Unfortunately, Scientists have not agreed on what it was. Roughly two billion years later, these prokaryotic cells combined to form the first eukaryotic cells.
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