> As Marshak alludes, finding out what happened during, and led to, the missing billion years is no trivial matter. There are two reasons for this. The first is that it just so happens to have occurred immediately before another inexplicable event – the sudden proliferation in the diversity of life on Earth 541 million years ago.
> Today geologists know that the youngest of the hard, crystalline rocks are 1.7 billion years old, whereas the oldest in the sandstone layer were formed 550 million years ago.
Isn’t this backward? Why is the oldest about 1 billion years later than the youngest?
Maybe it helps if I remove some of the details: youngest of group A is x years old, oldest of group B (which is different from group A) is y years old
Oh thanks, that makes sense. I found that phrase very confusing.