The Moon's ancient atmosphere

For nearly 70 million years, the Moon had an atmosphere formed by volcanic gas.

The Moon has been through some rough times. Just a few hundred million years after its formation, it experienced what astronomers like to call the period of Late Heavy Bombardment. During this time — lasting from about 4.1 to 3.8 billion years ago — the Moon (and indeed, the entire inner solar system) endured endless artillery strikes from interplanetary debris. On the Moon, this triggered a series of volcanic eruptions that left its surface a hellish landscape filled with lava flows that stretched on for hundreds of miles.

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