Home > Ephemeris Program, History, The Moon > Ephemeris: 02/10/2025 – How old are the features on the Moon?

Ephemeris: 02/10/2025 – How old are the features on the Moon?

February 10, 2025

This is Ephemeris for Monday, February 10th. Today the Sun will be up for 10 hours and 14 minutes, setting at 6:04, and it will rise tomorrow at 7:48. The Moon, 2 days before full, will set at 7:42 tomorrow morning.

In dating Moon rocks scientists get a range of dates from 4.6 to 3.3 billion years. An age of a rock is determined by the decay of a radioactive element one of which is uranium 238 decaying to lead 206. So the ratios of these two elements gives a date when a rock was last solidified. This clock is reset when a rock was last melted either by volcanism or by asteroid impact. It turns out that the rocks of the highlands, the lighter area on the Moon where most of the craters are, date to close to 4.5 billion years, and are probably the original crust of the Moon. The rocks from the lunar maria or seas are younger from about 4.1 billion years down to 3.8 billion years. So they were thought to be caused by asteroid impacts from the Late Heavy Bombardment.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.

Addendum

The Moon's geological eras in linear time
The Moon’s geological eras in linear time. The numbers on the right are in millions of years ago, thus 4000 = 4 billion years. The word Mare is pronounced Mar-e and is Latin for sea, and is the same as basin, because these are depressions. Credit: the Planetary Society, diagram by Emily Lakdawalla after Tanaka & Hartmann 2012.
The Moon's Geologic Time Scale (without numbers)
The Moon’s Geologic Time Scale (without numbers) Brown “U”s are supposed to denote impact craters. Red marks individual impact basins. The brown splotch denotes ebbing and flowing of mare volcanism. Credit: The Planetary Society, Emily Lakdawalla after Tanaka & Hartmann 2012.

The Late Heavy Bombardment is not accepted by all planetary scientists. The main evidence is the cratering and maria on the Moon.

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