Magnesium-rich rock known as komatiites form in the Earth’s mantle — the planet’s middle layer. They date back more than 2.5 billion years, to a period when temperatures in the mantle were boosted by radioactive elements inside it.
But scientists have found komatiite-like lava rock near Costa Rica’s Pacific coast that formed as recently — geologically speaking — as 90 million years ago. That suggests the mantle has regions near Earth’s core that may remain as hot as they were billions of years ago, said Esteban Gazel, a geologist and geochemist at the Virginia Tech.
Gazel is one of the authors of a study of the Costa Rican lavas, which was published today in the research journal Nature Geoscience. The site he and his colleagues studied is at the western edge of a geologic zone that’s being exposed as the Earth’s plates gradually move, revealing layers that had previously been deep beneath the surface.
How serious? The magma plume that left behind the Costa Rica rock he studied was responsible for forming much of today’s Central America and the Caribbean region — and in the process, fueled a collapse of oceanic oxygen levels that wiped out much of the marine life that predated the dinosaurs, he said.
“It didn’t trigger a mass extinction on the surface of the planet, but it triggered a mass extinction under water,” Gazel said.
Don’t panic: There’s no sign that any new plume is in the works. But some of today’s volcanic hot spots, such the Hawaiian or Galapagos islands, may give scientists future clues that can open that window a bit wider, he said.
“The more we understand the past, the better we’re going to know about the present and the future of the planet,” Gazel said.
Gazel and his colleagues, who included researchers from the United States, France, and Russia, also looked for signs of a mineral known as olivine to help them gauge the temperatures that produced the rock. Olivine contains microscopic beads of once-molten glass that’s trapped when the mineral cools; the low amount of volatile compounds remaining in that glass is an indication of how hot the material once was.
Analyzing that material pointed toward a temperature of nearly 1,600 degrees Celsius (2,900 Fahrenheit) — “something never found before,” he said. That’s about 400°C hotter than today’s mantle.
Geologists identified the Costa Rica site as an area of interest about 20 years ago. But at the time, scientists didn’t have the tools they needed to analyze the material as extensively as they do today. Improved materials, more sensitive instruments and increased access to tools like mass spectrometers have allowed scientists to peer more deeply into the rock than before, Ganzel said.
Read more at Discovery News