A microscope image from an experiment conducted for this study. The image contains glass (brown), large garnets (pink) and other small mineral crystals. The field of view is 410 microns wide, about size of a sugar crystal.
A study, published today in Science, uses laboratory experiments to show that the iron-depleted, oxidized chemistry typical of Earth’s continental crust likely did not come from crystallization of the mineral garnet, as a popular explanation proposed in 2018. The iron-poor composition of continental crust is a major reason why vast portions of the Earth’s surface stand above sea level as dry land, making terrestrial life possible today.
In 13 different experiments, the research team grew samples of garnet from molten rock inside a piston-cylinder press, a device designed to simulate pressure and temperature conditions inside magma chambers deep in Earth’s crust. The pressures used in the experiments ranged from 1.5 to 3 gigapascals—that is roughly 15,000 to 30,000 Earth atmospheres of pressure or 8,000 times more pressure than inside a can of soda. Temperatures ranged from 950 to 1,230 degrees Celsius, which is hot enough to melt rock.