I don't think Faith has brought that up at this time. She seems to suggest that the split between African animals and South American animals is just because that is where they happened to live. That this doesn't explain why there was no split before Pangea broke up has escaped her. Faith doesn't have a list of the things that need explaining so she is never aware that what she says doesn't make sense with the bigger picture.
I believe the early earth grew by accretion of materials supplied by asteroids, such as the one that produced the crater in the Gulf of Mexico.
Both of you are right.
The early earth during the late heavy bombardment grew because of a large flux of asteroids. By 3.8 billion years ago it had ended.
Since then there are tonnes and tonnes of material added by micrometeorites and the occasionally bigger hunk of rock but these amount to a tiny fraction of the current size of the earth so it isn't material to this discussion. The Chicxulub creator was formed billions of years after the LHB and isn't relevant.