Earth Institute News Archive
posted 11/01/04
Simulating the Creation of the Earth's Core, With the Help of Great Gray
Liz Cottrell, researcher at Lamont-Doherty Earth Observatory, and Great Gray, the machine that pressurizes rock and metal to 2 gigapascals (20,000 times the pressure at the surface of the Earth) and raises the temperature to 2500° C.
The Earth's core is hidden beneath 2,600 kilometers of rock -- a liquid iron sphere, about eight times bigger than the moon, which flows around an inner shell of solid iron and generates the Earth’s magnetic field.
There are many theories on how it was formed, but how do you confirm a theory about something that occurred 4.5 billion years ago and is inaccessible to sampling?
Liz Cottrell, a scientist at the Lamont-Doherty Earth Observatory, is giving it a shot.
The main theory of how the core was formed seems like something from a sci-fi movie -- billions of years ago, meteors melted the surface of Earth into a magma ocean. These meteors contained metals which melted and and sank to the bottom of the magma ocean, eventually passing through the Earth’s mantle to form the core.
Scientists know the core was formed due to metals like iron sinking to the center, but how did the sinking occur? Was it quickly in one process, or slowly over time?
Confirming which process would give scientists a clearer picture of what happened billions of years ago.
For her research, Cottrell relies on “Great Gray,” the nickname of the enormous pressurizing machine that transforms her rock and metal samples into molten liquid. Cottrell subjects a combination of rock and metal to pressures of two gigapascals (20,000 times the pressure on the surface of Earth now) and temperatures of 2500° C, which are conditions similar to those in the deep planetary interior.
After cooling it instantly (essentially “freezing” it), Cottrell records the distribution and behavior of rare noble metals such as platinum, gold, palladium and iridium. The distribution of these noble metals between rock and iron metal gives clues as to how metal transports through rock in high temperatures.
Cottrell has been working intensively over the past two years on this research, and hopes to complete it this winter. In an abstract, she writes that data are pointing towards the hypothesis where the Earth was once molten and the core was created in equilibrium with the mantle at a very high temperatures.
Says Cottrell, "It takes two full days to assemble an experiment, run the experiment in the press, and take it out to look at what happened. Quantitative analysis of the noble metal concentrations can take days. Over the years, I have run over 70 experiments on platinum alone to understand its behavior under these extreme conditions."
Has she tried to picture what the core forming would look like? "Yes. All the time. Any model based on experiments has to make physical sense, too."