Thankfully, the Holocene Impact Working Group and the mega-tsunami field geologists are funded well outside
Morrison's influence, even though Morrison continues to referee publication. Ground truth about what has hit (including comets) will be determined by them.

While iron meteorites are roughly 8% of meteorites, the Barringer Crater impact at 44,000 BCE was a large iron, and there were iron impacts in Alaska at 34,000(?) (the mammoth pepperer), Siberia in 27,000 BCE, and Campo de Cielo in 2325 BCE. Brenham was a pallasite (iron witrh olivine inclusions). If you had a fractured planetissimal 400 million years ago, the core would have been iron.

That said, the bulk of larger impacts in the last 12,900 years appear to have been comet and comet fragment hits.

The Earth will encounter Comet Schwassman - Wachman 3's stream in 2022, while asteroid 2004 MN4 comes under the com sats in 2029.