The dark material filling the Maria is actually dark, solidified lava from earlier periods of Lunar volcanism. Both the Maria and the Highlands exhibit large craters that are the result of meteor impacts. There are many more such impact craters in the Highlands.
Hereof, where are the lunar highlands?
Lighter surfaces are the lunar highlands, which receive the name of terrae (singular terra, from the Latin for Earth), and the darker plains are called maria (singular mare, from the Latin for sea), after Johannes Kepler who introduced the name in the 17th century.
How were the lunar maria formed?
The lunar maria /ˈm?ːri?/ (singular: mare /ˈm?ːre?/) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas.
How did the highlands on the moon form?
Chandrayaan proves lunar highlands were formed by magma. “The hot liquid, magma, seems to have flowed on to the surface and taken the form of lava. The rocky remains that floated to the top appear to have transformed into the Moon's highlands or mountains,” an Isro scientist explained.