According to the bible, afaik, the Earth is only 8000 years old. I have a hard time believing this.
Well to be fair, the Bible doesn't give any specific age for the Earth. What happened is that several biblical scholars and priests analyzed the number of "begats" that were mentioned in the Old Testament and they deduced that the Earth was only several thousand years old. Of course, it's still massively flawed and the fossil record completely contradicts that age estimate.
And the days in Genesis aren't true days. They're metaphor.