Earth was formed 4500 million years ago. Lets drop the "million" and call it only "years". And it had been livable just 100 years after that. So more or less the entire time after earth's formation, it had been livable.
But it has gone through periodic mass extinctions. And scientists have been able to trace the last 500 years of it. Here' the cycle :
70 years ago : 80% lost.
140 years before that : 80% lost.
50 years before that : 80% lost.
125 years before that : 96% lost.
70 years before that : 80% lost.
Note that these extinction events occur suddenly. Not gradually as we had been taught before. And emergence of life after that also occurs instantly. Not literally overnight, but "overnight" as in jurassic scale. Giving no time for Darwinian evolution to kick in.
This talks a lot about the future.