Geoscience Reference
In-Depth Information
the rocks so that they began to separate out, with the densest, iron-rich minerals sinking to
form a core. The new Earth was hot, probably at least partially molten, from the impacts,
from the energy released by its gravitational contraction, and from the decay of radioactive
isotopes. It is likely that many radioactive elements in the pre-solar nebula had been cre-
ated not long before in supernovae explosions and would still have been radioactively hot.
So it is hard to see how there could have been liquid water on the surface initially, and it is
possible that the first atmosphere was mostly stripped away by the force of the solar wind.
A chip off the block
The formation of the Moon had long been a mystery to science. Its composition, orbit, and
rotation didn't fit with the idea that it had split off from the young Earth, formed along-
side it, or been captured whilst passing it. But one theory does now make sense and has
been convincingly simulated in computer models. It involves a proto-planet about the size
of Mars crashing into the Earth about 50 million years after the formation of the solar sys-
tem. The core of this projectile would have merged with that of the Earth, the force of the
impact melting most of the Earth's interior. Much of the outer layers of the impactor, to-
gether with some terrestrial material, would have vaporized and been flung into space. A
lot of that collected in orbit and accreted to form the Moon. This cataclysmic event gave us
a companion which seems to have a stabilizing effect on the Earth, preventing its rotation
axis swinging chaotically and thus making our planet a more amenable home to life.
