Primitive mantle discovered.

The Earth may not be as old as we think it is according to scientists who believe they’ve found a piece of the planet’s primitive mantle.

Geologist Matthew Jackson and colleagues discovered a primitive Earth mantle reservoir on Baffin Island in the Canadian Arctic and analysis suggests the Earth may be between 4.55 and 4.45 billion years old.

The Earth was believed to be over 4.5 billion years old and chondritic – the chemistry being similar to some of the most primitive objects in the solar system, chondrites. This model assumes that the primitive mantle would have certain isotope ratios of helium, lead and neodymium, but was called into question five years ago by a team at Carnegie Institution, who suggested that the levels of neodymium recorded were too high if the Earth was indeed chondritic.

“We had been looking under the wrong rock,” said Jackson, who said the Carnegie finding prompted researchers to change where they had been looking to find evidence of the Earth’s mantle.

Finding a piece of the primitive mantle involves studying lavas – since lava has the same isotopic composition of the rock that melted to make it, testing lava is identical to testing the rock’s original composition. The lava is Baffin Island contains the correct ratios of all three chemical elements and may be the first evidence for the oldest mantle reservoir.

This study further challenges the idea that the Earth has a chondritic primitive mantle, and Jackson suggests an alternative: “The early Earth went through a differentiation event and the Earth’s crust was extracted from the early mantle and is now hidden in the deep earth; the hidden crust and the mantle found on Baffin Island would sum to chondritic.”