The mantle of the Earth. The 1800 mile thick section of the Earth’s interior between the crust, which we live on, and the core, the ball of molten metal at the center of the planet. Compared to the other two sections, its makeup is more variable, with sections closer to the core being made up of solid rock, and upper sections reaching their melting temperatures and becoming molten. The mantle is responsible for much of the interesting geological occurrences on the planet, the most impressive of which is likely volcanic eruptions, which occur when molten mantle rock is shoved upwards and reaches the crust.
Of course, volcanoes are only possible if the rock of the mantle is molten, which requires very high temperatures. This makes the question of the temperature of the Earth’s mantle one that scientists are very interested in solving. Scientists already know certain things about the Earth’s mantle, most importantly that there’s a boundary a couple dozen miles below the surface of the Earth that marks the point above which the rock begins to melt. To find the temperature of mantle rock, scientists should just have to find what temperature its components melt at, and derive it from that.
The main obstacle to this has been that the material most of the upper mantle is made of, peridotite, tends to have water within it, and it’s very difficult to control the amount of water to get it to match the Earth’s core. Previous attempts to account for this have found that the temperature of this boundary point is likely 1350° Celsius, or 2462° Fahrenheit. However, a new method to test the amount of moisture in a sample of peridotite found that previous samples weren’t dry at all, despite previous assumptions! As a result, they found that the temperature of the mantle is likely 60° above what had previously been estimated, or 1410° Celsius. While this number may seem relatively insignificant, previous changes to the temperature of the mantle had been around 10° or less, so this represents a substantial change to our understanding of what lies beneath our feet.