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SYFY WIRE geology

Ruby that hides 2.5 billion-year-old signs of life is one precious gem

Graphite in a ruby has been found to be a possible remnant of ancient once-living things.

By Elizabeth Rayne
Liz Ruby

If you own any piece of jewelry with a ruby, you’re probably never going to look at it the same way again.

Forget those perfect gemstones you see glittering in store displays. What scientists are looking for are the flawed ones — the ones that contain inclusions which can whisper the secrets of Earth’s distant past, like that tardigrade trapped in amber. When researcher Chris Yakymchuk and his team unearthed a peculiar ruby in Greenland, the inclusion they found was what remained of life that was over 2.5 billion years old.

What was inside the ruby sounds common enough. Graphite is the same material pencils write with, but it is also a pure form of carbon that Yakymchuk determined to be all that was left of prehistoric microbes, possibly the same cyanobacteria (blue-green algae) that first released oxygen into Earth’s atmosphere through photosynthesis. He led a study recently published in Ore Geology Reviews.

It was the isotopes of carbon in the ruby’s graphite inclusion that gave away the graphite as a possible remnant of once-living things. Lighter carbon takes less energy for cells to process.

“Life, whether humans, dinosaurs, or bacteria preferentially uses the light carbon isotope,” Yakymchuk told SYFY WIRE. “It is easier to make cells and other biological components with lighter building blocks. This leads to graphite that is enriched in light carbon.”

The two main isotopes in carbon are light carbon, or carbon-12, and heavy carbon, or carbon-13. It was the significantly higher amount of carbon-12 that told the researchers the ruby’s carbon must have come from living organisms. When dead organisms on the surface are buried, graphite can form when the heating reaches a point when it breaks down cells and releases most of the other components of what was once alive. This leaves behind carbon and hydrogen that make up fossil fuels, but if buried deeper, hydrogen no longer survives.

The pure carbon that is left from heating and compression underground can eventually turn into graphite. Another way carbon can morph into graphite is through ancient fluids that already contain the mineral, and when they escape from the depths of Earth’s crust, they deposit that graphite. What is really amazing is that carbon from organisms that died billions of years ago was not just a scientific find, but that the ruby couldn’t have formed without it. The presence of graphite means that CO2 was lurking somewhere in the surrounding rocks as rubies formed.

“We think that having CO2 in the rock generally helped with ruby growth in these particular rocks at the depths and temperatures of burial,” said Yakymchuk. "This is based on numerical modeling using the thermodynamic properties of the different minerals in the rock. If there was no CO2, it would have been difficult to grow ruby at these depths and temperatures.”

Even more hints are revealed by the graphite. Other rubies forming in the same location were dependent on CO2, and graphite being present means that they were, at one time, heated up to at least 932 degrees Fahrenheit. These are metamorphic rocks. Such rocks used to be sedimentary or igneous rocks that were heated and pressured into a sort of “metamorphosis” that made them what they are now. If these are igneous rocks, carbon can be derived from liquid magma reacting with certain fluids.  Earth really needs to turn up the heat to create rubies.

Many types of gemstones with inclusions could be time capsules, including diamonds, sapphires, and emeralds containing carbon that once fueled living organisms. There are still mysteries such inclusions could help solve. While it is known that chemical changes resulted in the Great Oxygenation Event that forever changed the atmosphere of our planet and made it much less vulnerable to impact gases from asteroid collisions eating up oxygen, the exact chemical changes are still buried somewhere in prehistory.

Yakymchuk is eager to keep finding inclusions that may elucidate what exactly happened to ancient Earth.

“Inclusions are snapshots of Earth’s history, and the gemstones themselves act as time capsules that preserve this information,” he said. “As we develop new tools and technologies, we can get more and more information from these microscopic features.”

If you see anything weird in a gemstone from your jewelry collection, you might want to take it to a museum.