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The Late Heavy Bombardment was a period of intense asteroid impacts occurring 3.9-3.85 billion years ago, evidenced by remelted rock samples from the Moon’s asteroids. Earth, Venus, and Mercury likely experienced a similar increase in asteroid impacts, causing serious environmental damage every 100 years. The oldest rocks on Earth are 3.85 billion years old, erasing evidence of the Hadean period, but life likely originated before this time.
The Late Heavy Bombardment is a period of highly intensified asteroid impacts occurring between 3920 and 3850 million years ago (mya). Life itself formed a few tens of millions of years before the late heavy bombardment or near its conclusion.
Evidence of the late heavy bombardment was found by Apollo astronauts visiting the Moon. Of all the rock samples they reported, many of them clearly remelted after asteroid impacts, and these remelting events were clustered with ages of 3920 million years or a hundred million years younger. This period of time was thereafter called the “lunar cataclysm.” The Moon’s asteroids have all been shown to have the age cutoff of 3920 million years, but are not grouped into the short period after that, having ages between 2500 and 3900 million years ago. By extension, it was inferred that Earth, Venus, and Mercury would also experience a substantial increase in asteroid impacts during this period.
If the late heavy bombardment had actually occurred, then this is the damage that likely would have been done to Earth:
22,000 or more impact craters with diameters greater than 20 km
about 40 impact basins with diameters of about 1000 km
several impact basins with a diameter of about 5,000 km
Serious environmental damage would have occurred every 100 years, making the planet a difficult place to live, even though the first years of life emerged during this time. Although the Earth had already cooled and solidified before this period, all elements of this geological era have been erased, because the late heavy bombardment has evidently destroyed most of the crust and therefore the oldest rocks to be dated have an age of 3850 million years. The earlier period is known as Hadean, after it, Archean. The oldest bacterial fossils don’t appear in the record until 3460 million years ago, but most who study early life believe it originated several hundred million years earlier.
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