Researchers at the Swiss Federal Institute of Technology (ETH Zurich) have demonstrated that a common mineral found in the Earth’s core and mantle has excellent thermal conductivity. This leads them to believe that the Earth’s heat is dissipating rapidly.
The evolution of the Earth is a story about its cooling. Approximately 4.5 billion years ago, the Earth was covered by molten rock (magma) beneath the oceans, creating extreme temperatures on its surface. Over millions of years, the Earth’s surface cooled, forming a brittle crust.
Measuring Earth’s heat takes place in high-pressure and extreme temperature environments – (Photo: ISTOCK)
The enormous thermal energy from within the Earth continues to escape through volcanic activity, convective mantle (the viscous rock layer beneath the crust and above the core), and tectonic plates (the Earth’s outer crust divided into several sections known as tectonic plates).
However, for many years, scientists have sought to answer the question: How quickly is the Earth cooling, and how long will this continuous cooling process last?
Scientists at ETH Zurich have demonstrated that the heat escape from within the Earth’s crust is related to the thermal conductivity of minerals located at the boundary between the Earth’s core and mantle.
This boundary layer consists of the viscous rock of the Earth’s mantle directly in contact with the molten iron-nickel of the core. A significant amount of heat from the Earth’s core escapes at this interface.
The mineral Bridgmanite forms this boundary layer. It is the most abundant mineral in the Earth and consists of a silicate compound – perovskite (ceramic materials with a crystal structure similar to that of calcium titanate, CaTiO3).
However, researchers have faced challenges in estimating the amount of heat this mineral transmits from the Earth’s core to the mantle, as experimental verification has proven nearly impossible.
Professor Motohiko Murakami and his colleagues from the Carnegie Institution for Science in Washington State (USA) developed a sophisticated measurement system that allows them to measure the thermal conductivity of Bridgmanite in the laboratory under common pressure and temperature conditions found within the Earth.
“This measurement system shows us that the thermal conductivity of Bridgmanite is about 1.5 times higher than previously assumed,” said Murakami. This indicates that the heat flow from the core to the mantle is also higher than previously thought.
“Our research findings may provide a new perspective on the dynamical evolution of the Earth. The study suggests that the Earth, like other rocky planets such as Mercury and Mars, is cooling down,” explained Murakami.
