Compare Earth to Mars and you'll notice several striking differences, from the presence of an oxygen-rich atmosphere and flourishing life on Earth to barren red rocks on Mars.
Scientists believe they have uncovered a key reason for these differences, hidden deep within Earth. Geologists have long known that the Earth filters out iron from rocks when they erupt to the surface.
What has long fascinated geologists is the discrepancy between iron amounts in the planet versus iron on Earth's crust. By mass, Earth is 35 percent iron, leading one to believe iron would be a large constituent in the rocks on Earth's surface. However, iron accounts for only 5 percent of Earth's crust. The process by which iron is removed from magma/rocks as they transition from the Mantle to Earth's surface has been in debate for decades. Now, a team of researchers from Rice University believes they have found a new explanation.
Taking a step back, it's important to consider Earth if the crust was composed of 35 percent iron. Like Mars, this would leave Earth's surface largely a deep red color. As iron oxidizes (rusts) it takes on a deep red color, a process you've witnessed if you've ever been to Red Rocks Amphitheater in Denver or the Grand Canyon.
When iron oxidizes it binds oxygen to iron, an efficient and long-term process to remove oxygen from the atmosphere. If Earth's crust were comprised of 35 percent iron, a large percentage of oxygen from Earth's atmosphere would be bound in iron as it begins to rust. Therefore, the lack of iron at Earth's surface is a large reason Earth doesn't look similar to Mars: red, barren, and lacking oxygen.
The research team focused on a discrepancy whereby more iron is removed from magma the thicker the crust it has to travel through. The team reasoned there is likely some process to remove iron from magma as it travels through continental crust.
They argue that the process of removing iron is related to garnet, a common mineral on Earth, and commonly seen as the reddish mineral found in granite countertops. As molten rocks travel through Earth's crust on their way to the surface, it appears the temperature and pressure along with an abundance of garnets produce iron-rich garnets, which are too heavy to continue the journey to the surface. This process efficiently removes iron from the Mantle melt.
The team notes that if iron were not removed before reaching the crust, the iron would suck the oxygen out of the atmosphere, leaving Earth to resemble Mars.
What's quite incredible is the impact this small chemical process taking place kilometers in the Earth has on the surface. Without the removal of iron, Earth could quite possibly look like Mars, lacking oxygen, red, and barren of life.
