People have long speculated on the wonders that might be hidden deep within the Earth's surface. While so far no one has found dinosaurs, an interior black hole, or a breakaway Nazi civilization, geologists have found evidence for a vast and mysterious reservoir of primordial magma that has been completely undisturbed for more than 4 billion years. They haven't quite found it yet, but they've found some compelling and shiny evidence: a treasure trove of rare super-deep diamonds older than Earth's moon.
The super-deep diamonds are recognizably different than the well-known diamonds formed at more shallow depths (you know, the ones we've been conned into caring about by the De Beers Group) and were discovered when volcanic eruptions in Brazil brought them to the surface. In their paper recently published in Science, researchers say that examining these diamonds has resulted in chemical proof that a magma reservoir which has remained stable and unchanging since the formation of planet Earth does in fact exist. Geochemist Suzette Timmerman of the Australian National University says:
"Diamonds are the hardest, most indestructible natural substance known, so they form a perfect time capsule that provides us a window into the deep Earth."
Earth's mantle is the layer that is squeezed between the molten core of our planet and the outer crust (where we live) and is nearly impossible to study. It's hundreds of miles straight down and not only would it be impossible to drill down there, the heat and pressure would simultaneously crush and boil anything we might send down. We think that the Earth's mantle is solid, but since the 1980's there has been speculation that there may be a reservoir of the "primordial soup" that hasn't been turned over and solidified in the few billion years the planet has been around.
The theory is based off isotopes of helium found in volcanic lava. Some volcanic lava has a remarkably high ratio of helium-3 to helium-4. This unusual ratio of helium isotopes is also found in extremely old meteorites that have fallen to Earth, but not in the rock an soil we find up here on the crust. But because the ancient helium signature is only found coming out of the hottest volcanoes, it's impossible to tell where it originated.
According to researchers, this batch of super-deep diamonds offers proof that the primordial reservoir exists. The diamonds contain trapped remnants of helium that may have been formed before the collision that created the Earth's moon. According to the researchers, finding the isotopic pattern in these diamonds means that the helium must have come from where the diamonds were formed, or even deeper. According to Tinnerman:
"My research is unique in that it gives the first direct depth constraints on where this primordial reservoir is located (more than 410 km depth), as we know the diamonds formed in the transition zone (410-660 km depth)."
Eargh scientist Matthew Jackson from the University of California Santa Barbara, who was not involved in the research but has studied the helium isotope patterns for decades, believes this is an important step forward. He says:
"This is an interesting result, with a lot of potential to 'map out' where elevated 3He/4He domains are located in the Earth's deep interior
Helium can diffuse rapidly at mantle conditions, so it will be important to evaluate whether the ancient helium signature reflects compositions trapped at diamond-formation depths, or the composition of the host lava that transported to diamonds to the surface."
It's amazing how much we're finding out about the composition of our own planet, and how much we still have yet to learn. It's also amazing that we've been sold the idea of the extreme rarity of diamonds when they quite literally shoot out of the ground.