Here's what you should know about them:
* Origin: They are vast, dark plains of solidified volcanic basalt, formed by ancient volcanic eruptions billions of years ago.
* Appearance: They appear darker than the surrounding lunar highlands because the basalt is a darker material than the lighter-colored, heavily cratered highlands.
* Naming: The names "maria" are Latin for "seas", as early astronomers believed these dark areas were bodies of water.
* Examples: Some well-known maria include Mare Tranquillitatis (Sea of Tranquility), Mare Serenitatis (Sea of Serenity), and Mare Imbrium (Sea of Rains).
Fun fact: The maria cover about 16% of the Moon's surface.
