i think when the moon cooled down.
craters
Maria is a bunch of Basaltic material (which is igneous rock) that came together on the moon. It formed when the moon cooled. People used to think that the dark spots (maria) on the moon were oceans.
The moon is a sphere about one- seventh of the earth's size. It has dark spots and bright spots and craters.
They were created by meteors hitting the moon and making craters.
Reforming
The Moon is still called a lunar MARE.
mineral
In one way it has craters. The other is it has dark spots.
They thought they were lunar "seas" like the oceans on earth. They are actually vast plains. But even today, they are still called "seas".Many early astronomers thought the dark spots on the moon were "seas". That is how all the lunar maria got their name, such as "Mare Tranquillitatis" which translates into "The Sea of Tranquility".
They are called maria. They were formed when asteroid and comet impacts on the moon exposed the mantle of molten rock. The lava flooded into and over the craters and hardened in vast fields forming the dark spots we see when we look up at the moon.
The moon has plains,mountains,and many craters. The moon also has unactive volcanoes and dark spots called seas.
by looking at the the dark areas thruogh a telescope