That's deep, man...

Scroll down through this graphic to see the full range of height and depth from the earth that humans have gone (not including space). And yes, this chart means that you need oxygen to get to the top of Mount Everest - everyone who climbs it has to carry it with them.

 Also interesting to note is the depth of Deepwater Horizon, which you might recognize from one of the worst environmental disasters in human history - almost 5 million barrels-worth of oil spilled into the gulf of Mexico, as the incredible depth made the well extremely difficult to close. The next largest oil spill was "only" 1.3 million barrels.

As for that Kola borehole, the deepest we've ever gone, here's a video breakdown of what we learned:

And here's what it might sound like to drop something down there...and here's a comic about the supposed sounds down there.

Even with these "huge" heights and depths, the earth is SO big that it's actually relatively smooth. In fact, if you shrunk the earth down to the size of a pool ball, it would be SMOOTHER THAN THE POOL BALL. Awkwardly, it wouldn't be round enough though - the earth is actually a little wider at the equator, not a perfect sphere. (source)

I'm not sure what else to add here, but I'd love to answer some questions if you have any! And if you have any science tips or possible future blog topics, let me know at barrentine@mewebacademy.org