"When a large body strikes Earth, impact debris can be accelerated to
orbital speed and achieve Earth orbit. Four billion years ago Earth was
probably surrounded by debris ejected in this way. (The Moon itself is a big
piece of Earth that sundered when a Mars-sized planetestimal hit 4.5 billion
years ago.) During the Period of Heavy Bombardment, the Moon was
considerably closer to the Earth than it is now, perhaps 3 times closer.
This placed the Moon in an ideal position to sweep up some of the
terrestrial debris."
The piece goes on to speculate that there may be many early Earth rocks,
some carrying early bacterial life, lying about on the moon's surface. This
brings two questions to mind:
1. What must be the momentum vector of a body impacting early Earth for it
to place debris bodies into Earth orbit?
2. We read much about meteor impacts during Earth's formation but I've never
read anything about Earth's size during most of those impacts (4.5 to 4.0
gigayears ago) or how long it took for Earth to grow to its present size
given that every impact not only added to but likely subtracted from Earth's
mass. Has any planetary scientist addressed this question?
poj
This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.