Monday, March 17, 2014

Springs of the great deep

A brown diamond containing water-rich ringwoodite
formed in earth's mantle.  Credit: University of Alberta.
Image source.
Throughout elementary school, students are taught that the earth is composed of several layers, including the thin hard crust, the plastic mantle, the hot liquid outer core, and the very hot solid inner core.  They are presented as known fact, as if the layers have been observed and documented.  I remember being quite surprised that our "knowledge" of the interior of the earth comes almost entirely from seismic waves passing through it.  The pattern of wave refraction does indeed suggest such a structure, but people perhaps overestimate just how much we actually know about the composition of our own planet.

Last week, the University of Alberta reported on a unique diamond found in Brazil.  Unlike the diamonds found in jewelry, this particular specimen contained many impurities and flaws, making it a virtually worthless "brown diamond."  The 3 millimeter rock was purchased for $20 by a geologist graduate student who was searching for an unrelated mineral.  Upon closer inspection, the brown diamond was found to contain a bit of ringwoodite, a mineral typically found in meteorites and theorized to exist in the mantle.  Before this discovery, however, no ringwoodite had ever been found that did not originate in space.

Obviously, this find excited the geologists, who studied the sample using multiple tools and methods.  During these investigations, they found that about 1.5% of the mass of the ringwoodite was made up of water, implying significant water reserves deep underground in the mantle, where the rock is thought to have originated.  Several news sources have depicted these water reserves as great subterranean oceans, such as those described in Jules Verne's Journey to the Center of the Earth.  However, the scientists suggest that the water is contained within the rocks themselves, akin to a giant deep aquifer.  Aquifers hold water not like a bathtub, but more like a sponge or wet sand.

Scientists have previously hypothesized large underground water reserves in the mantle, specifically in the "transition zone" between the upper and lower mantle, due to the strange behavior of seismic waves in this area.  The proposal of water in this zone has remained controversial, but this latest study is the first direct evidence of water so deep in the ground.  Interestingly, several creationists have also proposed great underground water reserves based on Bible passages that refer to the "waters below" during Creation Week and to the "springs of the great deep" which broke open at the beginning of the Flood.  Non-creationist geologists, on the other hand, interpret the water as having been brought down by subducting oceanic plates.  As the ocean floor slides underneath a continent, such as happens on the west coast of America, it brings some water with it into the mantle.  This water then seeps into newly-forming minerals such as diamonds, which are eventually blown to the surface via volcanic pipes.  This model could also have happened in the creationist view while the plates were moving at accelerated rates during the Flood.  It would be interesting to see if there is any correlation between subduction zones and the deep water reserves.  If so, then the water was likely brought down by subducting plates.  Otherwise, they may have been part of the original creation and helped start the great Flood.

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