View of the basalts along the northeastern coast of Baffin Island.
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Image Courtesy of Don Francis, McGill University
Oldest Earth Mantle Reservoir Discovered
The Earth's mantle is a rocky, solid shell that is between the Earth's crust and the outer core. The mantle is made up of many different reservoirs that have different chemical compositions.
Scientists had already determined that the Earth was slightly older than 4.5 billion years old, but had not found a piece of the Earth's primitive mantle.
Until five years ago, scientists thought the Earth's chemical composition was chondritic. This means that the mantle was similar to that of chondrites, which are some of the oldest and most primitive objects in the solar system. Chondrites have a certain ratio of the chemical elements of helium, lead, and neodymium. But five years ago, scientists learned that the ratio of neodymium was higher than previously thought.
This new information meant that scientists needed to look in different places for the Earth's primitive mantle. Since many of the ancient rocks have melted over time, finding a piece of the primitive mantle means studying lavas.
They looked at lava samples from Baffin Island and discovered that the sample had the correct ratios of all three chemical elements--helium, lead, and neodymium. This discovery means that the sample from Baffin Island is the first evidence for the oldest mantle reservoir. This discovery will help scientists understand the composition of the original, early Earth.
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