How Do You Take the Earth’s Temperature? Check Out Undersea Volcanos

(Inside Science) -- How do you take the Earth’s temperature? Scientists need this vital figure to assess our planet’s geological past and its future. But you can’t just wrap the Earth in a blanket and ask it to suck on a thermometer.

Scientists have long struggled to find the best way to measure the Earth’s interior temperature, and the many different approaches have produced many different answers. “I started this project because it was just driving me crazy,” said MIT geochemist Stephanie Krein, the lead author of research that estimates the Earth’s temperature by examining basaltic rocks -- rocks that were once molten lava but have since hardened.

Krein, MIT geologist Tim Grove and their colleagues have used the new method to develop a model of the Earth’s oceanic ridges -- a massive chain of undersea volcanoes, hotspots and submerged mountain ranges that snake around our planet at the edges of its tectonic plates. Cold ocean water turns the hot molten lava erupting along the ridges almost instantaneously into “sea glass.” These volcanic rocks can preserve chemical details about their origins. Research ships have gathered sea glass samples along oceanic ridges for decades now, and the MIT researchers tapped this collection to build their model.

Grove explained that the model uses data from the samples to determine both the temperature and pressure they melted at. “It’s based on an extensive set of experiments from our laboratory here at MIT and from other laboratories around the world where people have melted mantle materials,” he said. “We’ve used those to create this expression that can be used to predict the composition of the melt that’s coming out of the mantle.”

The diagnosis? The temperature of the Earth’s upper mantle beneath oceanic ridges is mostly constant at about 1,350 degrees Celsius (2,462 degrees Fahrenheit), but it rises beneath hotspots to about 1,600 C (2,912 F). Krein hopes the results will help scientists understand the behavior of tectonic plates and how they may have contributed to conditions on the Earth that can sustain life. “We are constantly stressing how [plate] tectonics operated in the past,” she said. “And so I think it’s really important for us to be able to understand how tectonics are working in the present day.”

Geochemist and volcanologist Ken Rubin of the University of Hawaii, who was not involved in the new research, said the method could become a useful tool for earth scientists. “Studies like this provide important constraints on the potential range of conditions deeper beneath Earth’s surface,” he wrote in an email. “This paper reports the creation and use of a tool to more easily make calculations that people have been doing in one form or another for several decades.”