The brilliant, shiny stones that we often associate with wealth and grandiose living, in truth, have quite literally down-to-Earth origins. These gemstones are really just mineral crystals, forged deep within the Earth by eons of geologic forces and chemical reactions.
In fact, most of the famous gemstones that we know of are really just arrangements of what are otherwise run-of-the-mill elements. Diamond, as most of you will know, is composed of carbon (C) atoms arranged in a lattice. The gemstones ruby and sapphire, on the other hand, are merely just the same crystal of the mineral corundum, composed of aluminum oxide (Al2O3)—the difference being rubies gain their color from chromium (Cr) atoms here and there, while sapphires often come in a variety of colors and whose atomic “substitutions” include titanium (Ti), vanadium (V), or magnesium (Mg), among others.
Amethyst is really just purple quartz, the makeup of which is mostly silicon dioxide (SiO2) mixed in with other impurities—and yes, it’s mostly made of the same stuff as usual beach sand. Finally, emerald is a variety of the mineral beryl (Be3Al2(SiO3)6) with some chromium or vanadium mixed in here and there. Overall, these five gemstones came to be known as the five cardinal gems of antiquity, and were famous for their relative rarity and apparent value.
Now, seeing as these gemstones all come from the ground, they too carry clues about the planet’s past. And since these mineral crystals offer clues as to how they were made with whatever is left inside them as they formed, we can use their presence in the rock as clues towards the history of that said rock as it stretches back eons.
A particular study published in the journal Ore Geology Reviews appears to have done just that. In studying rubies obtained from the North Atlantic Craton, which are among the oldest patches of land on Earth, they found something spectacular: graphite, the other naturally-occurring pure carbon allotrope aside from diamond. Thing is, it’s not just random carbon stuck inside a gemstone; it appears to be remnants of something even more special.
The craton in question is located in southern Greenland, where the special ruby was found. The study was led by University of Waterloo Earth and Environmental Sciences professor Chris Yakymchuk, who worked together with a team of scientists.
Clues to the true uniqueness of the carbon present in this particular ruby came about when they analyzed the carbon inside for its isotopic abundance. See, just as how pure carbon can be found in nature in different ways—graphite or diamond—atoms, too, can vary from each other. Their differences, however, come in the number of neutrons they have in them.
Carbon in nature comes in two different stable isotopes, depending on how many neutrons it has within its atoms. The most common carbon isotope on Earth is carbon-12, comprising about 98.93% of all carbon on Earth; it contains six (6) neutrons within itself. The other roughly 1.1% of carbon on Earth is composed of carbon-13, which in turn contains seven (7) neutrons.
Out in the world, rocks bear no preference towards one or the other, so the abundance of the two isotopes are fairly predictable. On the other hand, the relative “lightness” of carbon-12 compared to carbon-13—due to the one-neutron difference in composition—makes carbon-12 highly preferable for living organisms, as it takes less energy to use it in biological processes compared to carbon-13. Thus, the isotopic abundance of carbon in organisms is different, and identifiable, compared to carbon’s abundance out in nature.
Yakymchuk and team took advantage of this fact when they determined the isotopic abundance of the graphite in the ruby, and found it to be predominantly carbon-12; as it turns out, the graphite locked inside the ruby was likely from living organisms from a time before the graphite and ruby formed. The ruby likely formed some 2.5 billion years ago—meaning the graphite inside it formed at around the same time, and were most likely microorganisms like bacteria from a time when the planet’s atmosphere was just starting to accumulate oxygen through the Great Oxidation Event.
“Living matter preferentially consists of the lighter carbon atoms because they take less energy to incorporate into cells,” Yakymchuk said. “Based on the increased amount of carbon-12 in this graphite, we concluded that the carbon atoms were once ancient life, most likely dead microorganisms such as cyanobacteria.”
“The graphite inside this ruby is really unique,” Yakymchuk said in a statement. “It’s the first time we’ve seen evidence of ancient life in ruby-bearing rocks.”
And, just as mentioned earlier, the presence of carbon within this particular ruby gives Yakymchuk and team clues into how the ruby formed—something that’s “impossible to [determine] directly based on a ruby’s colour and chemical composition,” according to Yakymchuk.
The research team also concluded that the presence of graphite suggested the presence of fluid, which would have driven out silicon dioxide from the area. This left the area primed for the eventual formation of the ruby around it.
(For other relevant reads, check out our earlier piece on the problems surrounding locating the oldest evidence for life on this planet. Likewise, check out our piece on how asteroids may have delayed its eventual buildup in our atmosphere, and how the oxygen that we breathe in may not stay around on Earth forever.)
References
- Bleeker, W., & Davis, B. W. (2004). What is a craton? How many are there? How do they relate? And how did they form? 2004, T41C-01.
- Saplakoglu, Y. (2021, October 24). 2.5 billion-year-old traces of life locked inside primeval ruby. LiveScience. https://www.livescience.com/ancient-life-inside-primeval-ruby
- Starr, M. (2021, October 22). For the first time ever, evidence of ancient life was discovered inside a ruby. ScienceAlert. https://www.sciencealert.com/evidence-of-ancient-life-has-been-found-trapped-inside-a-ruby
- Waterloo News. (2021, October 21). Some of the world’s oldest rubies linked to early life. Waterloo News. https://uwaterloo.ca/news/media/some-worlds-oldest-rubies-linked-early-life
- What is corundum and what are its basic qualities? (n.d.). Retrieved October 27, 2021, from https://www.eoas.ubc.ca/courses/Dist-Ed/eosc118-webpromo/01-modB-les17-webpromo.html
- Yakymchuk, C., van Hinsberg, V., Kirkland, C. L., Szilas, K., Kinney, C., Kendrick, J., & Hollis, J. A. (2021). Corundum (Ruby) growth during the final assembly of the archean north atlantic craton, southern west greenland. Ore Geology Reviews, 138, 104417. https://doi.org/10.1016/j.oregeorev.2021.104417
