How did the
Earth Get Here?
Making the Periodic Table of Elements via Stellar Evolution
The Relative Abundances of the elements
reflects these fusion reactions.
To get beyond iron requires Supernova and neutron capture:
- Supernova represent massive stars that go bang
- Pre-supernova star is heavily layered
- They are very important sites to make the heavy elements
- Elements heavier than iron are built up by neutron capture.
Neutron Capture: Two processes:
In the solar system (meteorites) most heavy elements are proton-rich
indicating S-processed elements, but some R-processing occurred which
is of very important consequence to the earth.
But R-processing produced a small bit of Uranium which is extremely important.
- U-235/U-238 = 0.31
- U-235 has 1/2 life of 700 million years
- U-238 has 1/2 life of 4.5 billion years
- U-238 drives plate tectonics!!!