Late Heavy Bombardment (LHB) has been part and parcel of the naturalistic version of Earth history since it saw daylight after scientists assumed they saw marks of asteroid strikes in moon stones collected by Apollo astronauts in the 1970s.
Now, however, “the once-popular theory has come under attack, and mounting evidence is causing many researchers to abandon it. A growing community of planetary scientists thinks that things quietened down relatively quickly, with a steadily decreasing rain of asteroids that ended a few hundred million years [sic] after Earth and the Moon formed,” a feature article in Nature says.
The age of the rocks was obtained “by measuring the rocks’ ratio of argon-40 atoms to radioactive potassium-40.”
The article admits that there is “ambiguity in the rock dating…[because] at high temperatures … 40Ar can leak out of minerals.”