1. Maria (singular: mare): These are the dark, smooth plains that cover about 16% of the lunar surface. They are actually vast, solidified lava flows that filled ancient impact basins billions of years ago.

2. Highlands: These are the lighter, heavily cratered, mountainous regions that cover the rest of the Moon's surface. They are older than the maria and are thought to be composed of anorthosite, a type of rock rich in calcium and aluminum.