How do scientists know how old the Earth is?

It’s a question humans have grappled with for centuries – how old is the Earth? 

For a long time in the Western world, the history of our planet and species was derived word-for-word from the Christian Bible.

Back in 1642, John Lightfoot, an English clergyman, calculated what he thought to be the exact date of the creation of the universe: September 17, 3928 BC. He arrived at this conclusion by counting backwards through the epic genealogies recorded in the Bible

According to science, however, the Earth is a much older rock. It’s been labouring around the sun for 4.54 billion years, in fact, which we often round down to 4.5 billion. 

Now, it may seem a very specific number, but that age actually has an error margin of around 50 million years each way – no small sum of years, but a pretty tight margin in the grand scheme of things.

So how can scientists peer back into the misty past to actually know how old our planet is? And how have they narrowed the number down so much?

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