Most scientists agree the precious metals – gold and the six platinum group elements – were added to Earth’s surface sometime after it formed 4.5 billion years ago. In the late 1980s, scientists debated how this happened. Some thought these elements were added to the Earth’s mantle and crust by countless asteroid impacts during the Late Heavy Bombardment 4 billion years ago, while others believed they came from the collision of Earth and Theia, a planetary body the size of Mars, which spawned our moon 20 million to 100 million years after the solar system’s formation. After several years of debate, in the early 1990s most researchers decided the evidence pointed toward the Late Heavy Bombardment theory, and the Theia theory fell out of favor. Now, a new study argues the collision of Earth and Theia could still be the source of the precious metals, reviving the abandoned theory. Norman Sleep, a geophysicist at Stanford University, performed new calculations to show Theia’s core contained enough material to account for the platinum group elements in Earth’s mantle and showed how oxygen in the planet’s mantle could have helped to keep them there. http://blogs.agu.org/geospace/2016/...are-earth-metals-provide-clues-lifes-origins/
