h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Good summary.

Maria -
a)The moon's rotatation is almost synchronous with its orbit which means that only 60% or so of the surface is visible from earth, ie facing earth. I remember one school of thought that suggested that earth's gravitational field may have influenced the formation of the maria. Is this still current?

b)The reason they were called mare (latin = sea) is that early astronomers saw mountains around flat areas which were darker. This suggested seas. Most 'mistakes' like this were made because the truth was beyond their experience. (One 17 th century writer had the hero harness geese to a kite and then flew to the moon!)

Very nice entry

Just one suggestion for the geological composition part, mare areas are indeed lava flows, but it migth be worth mentioning that these lavaflows were triggered/created by massive impacts. Moon's own heat production wouldn't have been able to create such enormous amounts of molten rock. Well, that is atleast what they teached me?

And one other thing, sedimentary rocks cover most of the surface of Earth, while metamorphic and igneous rocks make up most of the volume in crust. This actually might be? your original idea, but little rewriting in that area migth clear it up a bit.

But otherwise and well worthy to get into the edited guide!!