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How did Apollo lunar samples help scientists determine the ages of Moon regions?
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Meteorite crater
Four impact craters of the same size (30 km [20 miles] in diameter) imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. The images are oriented such that the craters appear illuminated from the left; the Venusian crater is imaged in radar wavelengths, the others in visible light.
The Apollo lunar missions were instrumental in establishing a timeline for the Moon's geologic history by providing physical samples that could be analyzed in laboratories on Earth.1
Scientists determined the ages of different lunar regions through the following process:
- Crater Counting: By performing simple counts of craters larger than a specific size per unit area, researchers can determine the relative surface ages of various regions. A higher density of craters generally indicates an older surface, while a sparseness of craters suggests more recent geologic activity, such as volcanic resurfacing.1
- Radiometric Dating: The Apollo samples allowed scientists to assign absolute ages to these regions. By using radiometric age dating, researchers measured the decay of radioactive isotopes within the returned rocks. Because these isotopes are trapped when a rock cools from a molten state, they act as a clock to measure the time elapsed since the rock formed.2
By correlating the absolute ages obtained from these laboratory-dated samples with the crater counts observed in the specific regions where they were collected, scientists established a reliable method to estimate the ages of other lunar areas.1