How old is the earth and how did scientists find this out

By dating the rocks in the ever-changing crust, as well as neighbors such as the moon and visiting meteorites, scientists have calculated that Earth is 4.54 billion years old, with an error range of 50 million years.

Hello :)

The Earth is 4.543 billion years old

and we find out by scientific techniques of radiometric dating

Hope this helps and have a great day