The moon was much closer back then, just 14,000 miles away from Big Blue (though BB wasn’t very blue yet). Since its formation, the moon has progressively untethered itself from earth’s gravitational pull and and is now roughly 238,900 miles away (the moon is currently distancing itself from us by about 1.5 inches per year, though scientists think it will reach an equilibrium in about 50 million years). Back then the earth was also spinning much faster, so a day was only about 6 hours. If there had been water (and continents) the tides would’ve been incredible!
You’ll notice in the image above that the face of the moon we get to gaze up at has lots of dark smooth patches on it while the surface facing away from us is covered tip to toe in craters of all sizes. The darker areas are known as marias (okay, okay I know I said no Latin, but marias does mean sea in Latin), and are formed from lava flows. Today the moon’s surface is solid, so when an asteroid or comet crashes into it, it leaves a mark that will remain forever.
However, when the moon first formed, earth was so hot and the moon was close enough to earth that the heat was intense enough (earth was ~2,700 Kelvin) that it kept the face of the moon facing earth hot enough to keep from cooling solid. The far side of the moon, which faces off into the cold recesses of space cooled much quicker. All of those asteroids and comets pelting the moon that hit the molten side failed to leave lasting impressions in the lava sludge.
As the earth cooled and the moon distanced itself, the marias, or basaltic lava flows, cooled and solidified. These basalts are around 3 to 3.5 billion years old and their iron-rich composition makes them much less reflective than the surrounding craterous mountains (making them appear much darker from our vantage down here on earth). So our side of the moon is smoother and darker than the far side of the moon. There are tons of big marias and these are what give the moon that dolorous “Man on the Moon” vibe. Today, the moon is mostly solid but it does have a band of molten lava beneath the 740km thick solid mantle, and there are some features on the moon that suggest more recent lava flows.