Labels:text | screenshot | font | number OCR: MARE .............................................. A MARE IS a lowland plain on the Moon that appears to an observer as a dark area. Early astronomers believed these features were seas like those on the Earth. It is now known that lunar maria ("maria" is the plural of the Latin word "mare," meaning sea) were formed about 4 billion years ago when lava from volcanic eruptions flowed into huge meteor- impact craters and solidified.