One of the two locations on Earth where scientists found chemical signatures of early Earth’s mantle is Baffin Island off the coast of northern Canada. (Don Francis of McGill University)
According to most scientists, Earth was formed between 4.5 and 4.6 billion years ago after gravity forced gas and dust left over from the creation of the Sun accreted into an object called a planetesimal.
Over time, the planetesimal continued to gather more and more material and eventually became a planet.
Scientists say heat produced by this formation process caused our early planet to melt.
Illustration of an early and hotter Earth (Creative Commons)
The heat separated Earth’s material into layers with heavy matter such as iron sinking down to the center of planet to form its core.
Lighter and less dense material such as silicates floated above the core, subsequently forming what would become the Earth’s mantle and crust.
As the planet evolved, the mantle continued this process of melting and separating with heavier remnants sinking downwards and lighter material rising toward the top to form the Earth’s crust.
It’s thought this process, over the years, changed the chemical composition of the mantle to a point where any of the original ancient mantle material dating back to the core’s formation may have completely disappeared.
Now a consortium of US and Canadian research institutions say they have found two ‘birthmarks’ of silicate material from Earth’s mantle that may have formed when our planet was a mere 50 million years old.
Writing in the journal Science, the researchers say they’ve found clear signatures of this unique silicate material in comparatively young rocks from two locations that are a long distance from each other.
Schematic cross section of the Earth’s interior. (Northwestern University)
One of the samples of the ancient material came from Baffin Island, which is located off the coast of northern Canada, while the other was found in the Ontong-Java Plateau just north of the Solomon Islands in the Pacific Ocean.
The volcanic rock containing the primitive mantle signatures are known as flood basalts and were created about 60 to 120 million years ago by massive lava eruptions.
What led the researchers to detect the primordial mantle material in the volcanic rock was a profusion of an isotope of tungsten called tungsten-182.
Scientists say this tungsten isotope is created when an isotope of the element hafnium (hafnium-182) undergoes radioactive decay – changes in its elemental composition as it gives off radiation.
According to the researchers, the radioactive decay of hafnium-182 into tungsten-182 takes place so quickly – about 9 million years – that differences in the amounts of tungsten-182 compared to other tungsten isotopes can only be due to processes that took place very early in the history of our Solar System.
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