The sun and earth are around 4.5 billion years old. Simple cells may have existed for 3.6 billion years ago, fish from 500 million years ago (1 billion = 1000 million), primates 60 million years, modern humans from 200,000 years ago.
The Earth was formed about 4.5 billion years ago. Scientists have been able to figure this out by dating meteorites which have arrived on Earth – damaging but useful little things 😉
Really hard too add to the other guys answers since there is really only one answer. if you mean the Earth then 4.5 billion years, and if you mean the Universe then 17.7 billion years. Even though the Earth and the solar system only formed 4.5 billion years ago the elements from which it is made were either created in the big bang (13.7 billion years ago) for Hydrogen and Helium, or some other later time for the rest of the elements.
The heaviest elements were formed when the last generation of stars died. It is amazing to think that the heavier elements like Copper and Zinc that we have in our bodies were created in supernova explosions when old stars died. This means that our bodies are really made of stardust! How cool is that?
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