Mare (sea)

A mare in geological terms refers to a broad, flat plain on the Moon's surface, formed by ancient volcanic activity. These areas are darker and smoother than the surrounding highlands because lava once filled large impact basins, solidified, and created extensive basaltic plains. Though called “seas,” they are not bodies of water but solidified volcanic rock. Mare cover about 17% of the Moon’s surface and are key to understanding lunar volcanic history. Their relatively smooth terrain contrasts with the more cratered highlands, highlighting different geological processes that shaped the Moon over billions of years.