Page 46 - Curriculum Visions Dynamic Book

Far side Near side
 Near side and far side of the Moon. This image shows parts of both the near side and the far side of the Moon. The near side is to the right, the far side to the left.
The circular Orientale Basin, 1,000 kilometres across, is near the center. At the upper right is the large, dark Oceanus Procellarum; below it is the smaller Mare Humorum.
These features, like the small, dark Mare Orientale in the center of the basin, formed over three billion years ago as lava flowed.
At the lower left, among the southern cratered highlands of the far side, is the South Pole-Aitken Basin, similar to Orientale but twice the diametre and much older and more affected by cratering and weathering.
The cratered highlands of the near and far sides and the maria (”seas”) are covered with scattered bright, young rAy craters.
Near side of the Moon
A combination of giant impacts and lava outpourings has formed the largest features on the surface. Known as maria (singular mare, from the Latin meaning “sea”), they are the basins that can be seen as dark-coloured blotches on the Moon. Where lava has not formed, the land stands up as highlands and produces the bright areas that we see.
The main period when impact craters formed was during the early stages of the Moon’s formation. As a result, we can use the extent of cratering as a rough guide to the age of some surface features. The maria show the least cratering, suggesting that they are the youngest features. The highlands show many more craters and so are very old.
During the history of the Moon there has been considerable volcanic activity. Thin, runny, lava flooded up from the interior, covering vast areas very quickly. Only in a few places is evidence of more sticky lava found, which tends to make domes in the centers of craters.
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