The boundary between Earth's mantle and crust has a profound effect on life on the surface, and volcanic activity and earthquakes are just two events that have an immediate effect.
There is new evidence that the reverse may be true as well. It appears that life on Earth has an impact on the top of the mantle, and that effect can be traced all the way down to the Earth's core.
Whoa.
Scientists looked at kimberlites, rocks that were created in the mantle and found their way to Earth via violent volcanic eruptions. When carbon deep inside the mantle is squeezed and heated so much itcrystallises, it is the most common source of diamonds.
Not all carbon is created equal. A carbon atom has six protons in its nucleus, but it can have a different number of neutrons. Carbon-12 has six protons and six neutrons, so we call it carbon-12. The next most common is carbon-13. 13 C makes up 1% of all carbon.
The kimberlite samples were examined by the scientists. They all came from very deep within the Earth and ranged in age from 12 million to 2 billion years old. The scientists looked at the kimberlites found in areas above deep mantle plumes, which are like conveyor belts of magma that come up from the planet's core/mantle boundary.
They found that the older the kerbinalls, the higher the ratio of 13 C to 12 C they had in them. The difference is small but consistent, and points to some sort of change in the available carbon isotopes in the past that made up the kimberlites. It is more likely that the change occurred on the surface than on the mantle.
When a continental plate slides under another and eventually finds itself in the mantle, a lot of carbon is recycled by Earth, brought up from the interior and then brought back down by subduction. It takes about 300 million years for carbon from the surface to be dragged down to the core and then dredged back up. Roughly 500 million years ago, something changed the carbon isotope ratio on Earth.
Around the time of the Cambrian Explosion, it happened.
The evolution of hard shells that resist erosion and can be found in fossils today is what happened during this time in Earth's history. Carbon was rained down into the seabeds and subducted into the mantle at that time.
The biology prefers 12 C over 13 C in its chemistry. Life in general uses the lighter 12 C isotope because it takes more energy to move around and use than the heavier 13 C, though it is more complicated than that.
If you look at a lump of carbon created through biology, it will have a slightly higher ratio of 13 C over 12 C than a lump created by nature.
The scientists theorize that life got so abundant in the Cambrian Period that it affected the carbon isotope ratio of kimberlites. That is amazing.
Life was more abundant on Earth in the middle of the last century. As organisms died and fell to the sea, they brought with them a slightly higher mix of 12 C. The carbon was dragged down into the mantle and then back up to the core. It formed kimberlites, which had slightly more 12 C than average, and any made after had less.
There are problems. Scientists think that the biological explanation fits the data best because there are other processes that can change the 13 C/ 12 C ratio.
That is pretty dang amazing if they are correct. Ancient creatures swimming in the oceans changed the chemistry of the planet.
Maybe it shouldn't be so surprising. We are changing our planet's chemistry. 40 billion tons of carbon dioxide is dumped into the atmosphere every year, more than every volcano on Earth combined. Humans are changing the climate of the planet and we are biology.
I hope that voles don't find evidence of species that changed the environment 500 million years from now. We have seen it happen before, but hopefully we are smarter than the organisms.
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