> At some point, a satellite the size of Mars came crashing into the earth, so hard and so fast that about a third of the earth was blasted into space. It didn’t go far–the debris formed a ring around the earth, and gravity eventually compacted it into a single satellite, our moon, but a satellite much larger than our planet’s gravity would normally be able to capture.

Something seems off about "a third": according to https://en.wikipedia.org/wiki/Moon, the Moon's radius is a bit less than a third of Earth's, but its volume is 2% and its mass is just 1%. I'm no expert, but "about a hundredth" seems more accurate.

For what it's worth, I only looked it up because I've come across this discrepancy before, so perhaps I'm missing something!