Astrogeology: September 2019

The Moon-forming giant impact extensively melts and partially vaporizes the silicate Earth and delivers a substantial mass of metal to Earth's core.

A day is the time for Earth to make one complete rotation on its axis, a year is the time for Earth to make one revolution around the Sun -- reminders that basic units of time and periods on Earth are intimately linked to our planet's motion in space relative to the Sun. In fact, we mostly live our lives to the rhythm of these astronomical cycles.