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The Winter 2010 issue of The Earth Scientist includes a variety of educational resources, ranging from astronomy to glaciers. Check out the other publications and classroom materials in our online store.
An image of the heavily-cratered far side of the Moon.

The Moon's Geological History

Scientists have studied the ages of rocks in regions with craters and determined when in the Moon's past the craters were forming most quickly. By studying the light-colored regions, called highlands, they found that from about 4.6 to 3.8 billion years ago rocky debris rained down on the surface of the young Moon, forming craters very quickly. Then the rocky rain subsided, and fewer craters have formed since then.

Rock samples from very large craters (called basins) showed that about 3.8 to 3.1 billion years ago several huge, asteroid-like objects struck the Moon, just as the rocky rain was ending. This was shortly followed by lava flows which filled in the basins and formed the dark maria. This explains why there are so few craters on the maria, but dense, overlapping craters in the highlands. No lava flows occurred on the highlands to erase the original blanket of craters from the time when the Moon's surface was showered with the debris of the early solar system.

The far side of the Moon has only one small maria. So lunar geologists believe that the far side is very representative of how the Moon looked 4 billion years ago.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA