[ncmncm]

The article fails to note reasons why neither apparent existential risk was possible.

We already had moon rocks on Earth, blasted off of the moon by bolide strikes. Likewise Mars rocks, and bits of asteroids and of other planets' moons. Maybe even Venus rocks.

Relatedly, the energy released in certain bolide strikes on Earth far exceeds anything achieved even in Tsar Bomba, itself thousands of times more powerful than Fat Man.

I have not seen any analysis of whether a bolide strike might incidentally produce substantial fusion activity. At the pressure and temperature produced, it is hard to imagine it not occurring.

It seems like there ought to be long-lived products of such fusion detectable in the K-T layer, alongside whatever the bolide carried. Some might be weakly radioactive and thus detectable at very tiny concentration.

[mcswell]

"We already had moon rocks on Earth, blasted off of the moon by bolide strikes." True, but they (and any other meteorites) were likely sterilized during passage through the Earth's atmosphere.

[ncmncm]

It only takes a few minutes to get from the top of the atmosphere to the ground, not long enough to sterilize more than the surface.