William sent in the link to https://www.yahoo.com/news/earths-oldest-known-rock-found-211500968.html … Earth's oldest known rock has been found – on the Moon. The story is also at https://phys.org/print467624943.html … a rock found on the Moon, it has been shown, may have originated on the Earth. We are talking about a very small rock sample – examined minutely by scientists. It is just 1.8 grammes. It has a minerology similar to granite but this is thought to be rare on the Moon – so it must have originated elsewhere (and the Earth is closest). The sample also contains quartz – another Earthbound rock (and presumably another marker to its point of origin).
For another view of Ultima Thule go to https://phys.org/print467628327.html ….
… but lots to be clarified as data continues to arrive from New Horizons and continues to be sorted and analysed,
At https://www.sott.net/article/405687-Planetary-collisions-that-formed-the Moon-made-life-possible-on-Earth/ … planetary collisions that formed the Moon also made life possible on the Earth.