OK, so it is absolutely surprising that we know as much as we do know today about our ancestors, because it's incredibly difficult, A, for these things to become -- to be -- preserved, and secondly, for them to have been brought back up to the surface.
所以说，这是一件让人自豪的事情，我们对我们的祖先 能了解到我们现在所了解的程度， 因为这是及其困难的, 首先，这些东西要能被埋藏和保留， 其次，它们要能够重新露出地表面。