Researchers have found a primitive Earth mantle reservoir on Baffin Island in the Canadian Arctic. Geologist Matthew Jackson and his colleagues from a multi-institution collaboration report the finding--the first discovery of what may be a primitive Earth mantle--this week in the journal Nature.
The Earth's mantle is a rocky, solid shell that is between the Earth's crust and the outer core, and makes up about 84 percent of the Earth's volume. The mantle is made up of many distinct portions or reservoirs that have different chemical compositions.
Scientists had previously concluded 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 recently, researchers generally thought that the Earth and the other planets of the solar system were chondritic, meaning that the mantle's chemistry was thought to be similar to that of chondrites--some of the oldest, most primitive objects in the solar system. Assuming a chondritic model of the Earth, a piece of the primitive mantle would have certain isotope ratios of the chemical elements of helium, lead and neodymium.
The model that the Earth was chondritic was called into question with a discovery five years ago by a team at the Carnegie Institution of Washington, which suggested the ratio of neodymium on Earth was higher than what would be expected if the Earth were indeed chondritic.
That finding changed the neodymium ratio expected in the primitive mantle and in turn, changed where researchers should be looking to find evidence of a primitive mantle. According to the lead author, Matthew Jackson, "We had been looking under the wrong rock."
Since many of the ancient rocks have melted over time, finding a piece of the primitive mantle means studying lavas. Lavas retain the same isotopic composition of the rocks that have melted into the lava. Therefore, testing the lava's composition is id
|Contact: Kimberly J. Montgomery|
National Science Foundation