The Earth is cooling faster than initially thought, according to a report that appeared in the journal “Earth and Planetary Science Letters” this week, which could have grave implications to life on Earth. However, because of the grand scale of time Earth is on, any changes due to that cooling will take millions of years or more to impact life as we know it.
Titled “Radiative thermal conductivity of single-crystal bridgmanite at the core-mantle boundary with implications for thermal evolution of Earth”, the report by study authors says mantle convection is much more vigorous than expected and that more rapid mantle cooling is expected too.
The mantle is one of many layers that make up the planet. The three primary layers of the Earth according to USGS are the crust, the mantle, and the core. USGS says, “This layered structure can be compared to that of a boiled egg. The crust, the outermost layer, is rigid and very thin compared with the other two. Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km. Like the shell of an egg, the Earth’s crust is brittle and can break. ” USGS adds, “Below the crust is the mantle, a dense, hot layer of semi-solid rock approximately 2,900 km thick. The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter and denser because temperature and pressure inside the Earth increase with depth. As a comparison, the mantle might be thought of as the white of a boiled egg.” Continuing the egg analogy, USGS says the center of the Earth is the core, which is somewhat like the yolk of an egg. “Unlike the yolk of an egg, however, the Earth’s core is actually made up of two distinct parts: a 2,200 km-thick liquid outer core and a 1,250 km-thick solid inner core,” USGS explains.
The interior of the Earth is very important to life on its surface. As the Earth rotates, the liquid outer core spins, creating the Earth’s magnetic field. If the Earth’s magnetic field changed, life would be very different.
According to NASA, nearly all of Earth’s geomagnetic field originates in the fluid outer core. NASA explains, “Like boiling water on a stove, convective forces which move heat from one place to another, usually through air or water constantly churn the molten metals, which also swirl in whirlpools driven by Earth’s rotation. As this roiling mass of metal moves around, it generates electrical currents hundreds of miles wide and flowing at thousands of miles per hour as Earth rotates. This mechanism, which is responsible for maintaining Earth’s magnetic field, is known as the geodynamo.”
At Earth’s surface, the magnetic field forms two poles, also referred to as a dipole. The north and south magnetic poles have opposite positive and negative polarities, like a bar magnet. The invisible lines of the magnetic field travel in a closed, continuous loop, flowing into Earth at the north magnetic pole and out at the south magnetic pole.
Beyond helping a compass figure out which direction it is pointed in, the Earth’s magnetic field protects the planet from harmful solar radiation and space weather. This field, known as the magnetosphere, protects Earth’s atmosphere from eroding from solar winds, erosion and particle radiation from coronal mass ejections (CMEs), cosmic rays from deep space. Without it, radiation would drastically alter, if not kill, life on Earth. Unfettered solar winds reaching Earth would also destroy electronics, satellites, and most modern conveniences.
In the research report out this week, study authors studied bridgmanite, a common conductive mineral that is found between the Earth’s core and mantle. They found that it’s 1.5 times more conductive than previously believed, meaning Earth’s cooling process might also be faster than previously thought.
“We found the bulk thermal conductivity at core-mantle boundary becomes 1.5 times higher than the conventionally assumed value, which supports higher heat flow from core, hence more vigorous mantle convection than expected,” researchers added.
“Results suggest the mantle is more efficiently cooled, which would ultimately weaken many tectonic activities driven by the mantle convection more rapidly than expected from conventionally believed thermal conduction behavior.”
If the Earth’s core or mantle cooled to a point where it became solid, the magnetic field could cease to exist, bringing an end to life. Scientists are sure this could happen because it’s happened elsewhere in our solar system: Mars is a great example of this.
Recently, NASA’s Mars Atmospheric and Volatile Evolution (MAVEN) mission identified the smoking gun of what happened to Mars: it used to be much warmer, and had a thicker, more Earth-like atmosphere. NASA research shows that due to the lack of magnetic field protection, the majority of the Martian atmosphere was destroyed by the strong solar wind, with a barren, red planet left in its wake. Scientists assume the same will happen to the Earth’s atmosphere when its magnetic field shuts down too.
There’s no need to panic anytime soon though. While study authors didn’t pinpoint a date for when the cooling of the Earth’s insides would result in the end of the magnetic field, most scientists agree that such a phenomena is likely to be millions if not billions of years into the future.