Rocks dating from the birth of our planet 4.5 billion years ago have been found beneath the crust of the Earth, researchers determined. A pair of "birthmarks" have been discovered sitting in the mantle of our home planet, the region between the crust and the core.

Silicate material found in this layer took shape less than 50 million years after the Earth cooled, solidifying our planet. Evidence for this layer was found in two widely-separated regions of the globe - the Ontong Java Plateau in the Pacific Ocean, and Baffin Bay in the North Atlantic.

The early Earth is thought to have grown in size during its first few tens of millions of years through the accretion of material collected in a series of collisions with other bodies. The largest of these events, and the last, involved our planet being struck by a body the size of Mars. This powerful event resulted in the formation of the moon.

"What we've found are surviving parts of Earth's primitive mantle that have been preserved for four and a half billion years, and I think that's kind of exciting!" said Richard Walker of the University of Maryland.

This new finding would suggest that parts of the Earth's mantle are still left over, largely unchanged, since this ancient era. Previously, most researchers believed multiple impacts and heating would have mixed materials within the mantle, resulting in a largely homogeneous geological layer.

The first cracks in this idea were revealed in 2012, when researchers found material in the mantle dating to 2.8 billion years before our own time. Even this ancient date is twice as old as the first colonies of green algae in seas of our planet.

Ratios of radioactive isotopes can be examined in order to provide a record of events which occurred long ago, back to the birth of our planet. These ancient relics of the early Earth were identified from high levels of tungsten, a material formed from the radioactive decay of 182-hafnium. This element was present during the formation of our solar system, but is no longer found on Earth.

Analysis of the ancient material within the Earth's mantle was profiled in the journal Science.

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