Re #1, one really cool thing is that the remains of Theia (the other body that collided with Earth) may be visible in a big way in Earth's mantle still, if rece

Re #1, one really cool thing is that the remains of Theia (the other body that collided with Earth) may be visible in a big way in Earth's mantle still, if recent study is correct. See https://skyandtelescope.org/astronomy-news/bits-of-theia-might-be-in-earths-mantle/ https://skyandtelescope.org/astronomy-news/bits-of-theia-mig...