Under My Feet

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Underneath my feet, here in Burnaby, British Columbia is a wooden floor with a carpet, and below that a basement with pipes, wires, and concrete. Underneath that, there is soil, and sewage pipes. And further down is clay and rock, a lot of clay and rock!

You could go down for several kilometers, scooping up the same material until we reach the bottom of the North American tectonic plate. Along the way, you would be in complete darkness.

Juan de Fuca Subduction zoneBeneath this is the Juan de Fuca tectonic plate, or at least the burnt remains of it.1 As the North American plate slides West, it pushes more and more of the Juan de Fuca plate downward. The parts that have been submerged heat up, and are subjected to intense pressures.

20-30 kilometres below my feet,2 the melting Juan de Fuca Plate ends, and we get to the Earth’s Mantle, which is rock cooked really hot. Temperature ranges from 500 – 4000 degrees C. Normally, this would be hot enough to melt it, but the intense pressure from everything on top of it prevents the rock from expanding, which is necessary for melting to occur. So it remains as a syrupy solid.

Earth LayersThis humungous heap of magma goes really, really deep. If you were to somehow be able to go down into this, you could sink for thousands of kilometers. A flashlight would not be needed to see the magma as the burning substance is so hot it glows red. At greater depths, the temperature soars higher, the pressure gets more intense, and the chemical composition changes a few times. Then, 3000km down, it all transitions into the core.3

The outer core is a glowing, orange liquid. Its temperature ranges from 4000-6000 degrees depending on depth. The inner core is under so much pressure that it becomes solid again, despite the extremely high heat level. Its temperature is about 5400 degrees C, comparable to the surface of the sun.

At the very middle of the Earth, the influence of gravity is very small on the iron that is there, being mostly balanced from all directions. It is engulfed in bright, white light caused by the glowing hot metal. If the crust, mantle, and outer core were all transparent, it would look like there was another sun underneath us, glowing with incredible radiation. It is fortunate for us that the rock insulates us from it all, or it would be too hot for us to live here.

Looking beyond this point, most people would say that this is looking up again, or at least in a new “up.” But, for this post, I will continue to refer to that direction as “down” no matter how far I go, and this is where it gets fun.

Looking further in this direction, whatever it is, is the liquid outer core again, and then a new mass of solid mantle. Well, actually, it’s the same mass of mantle, just the south-eastern part of it instead of the north-west part I described before.

Continuing downward, the magma eventually softens into rock again, and it becomes a third tectonic plate under my basement, this time the Antarctic plate, one of the more northern areas of it.

A few kilometres further is the end of the ground under my feet. Beyond that is water, the southern area of the Indian ocean.4 In that water, there might be some clam shells, an occasional upside-down humpback whale, and possibly even sharks.

From http://trcwest.com/photoblog/2008/09/07/the-amazing-indian-ocean-by-night  -blue/Looking a couple more kilometers down, the water ends.5 At that spot, there is nothing but the sea in all horizontal directions. I am writing this in the daytime, which means it is night on the bottom of the Earth right now.

Beyond that is likely some clouds, and from that height (or depth), the Kerguelen Islands might be visible in the distance, assuming the moon shines brightly enough to see anything.

After that is a hundred kilometers of air, with the atmosphere getting thinner until it is practically nothing. Finally, at the end of the atmosphere, is the final layer that is underneath my feet: A bottomless, black pit.

Hubble Deep Field SouthIt is a pit so wide and so deep that it has stars and planets and even entire galaxies contained within it. What is at the end of it is hard to say. One could crash through stars and galaxies until the end of time. If you could travel faster than light, you might eventually cross into another universe, or loop around endlessly in our own, but since our telescopes can’t see all the way to the end, we may never know what’s really down there at the farthest depths of space.

Sometimes I look down under my feet, and think about the magma, the sharks, the empty sky, and the black pit that are all down there, and I feel afraid.

 

1http://www.uvic.ca/science/assets/docs/yearofscience/UVic_YearofScience_Plate_tectonics.pdf

2https://en.wikipedia.org/wiki/File:Mohomap.png

3https://en.wikipedia.org/wiki/Structure_of_the_Earth

4http://www.freemaptools.com/tunnel-to-other-side-of-the-earth.htm – This is a great resource that has two maps. When you scroll around on one, the other map shows you the opposite side of the world.

5Based on map at http://www.britannica.com/EBchecked/media/1996/The-Indian-Ocean-with-depth-contours-and-undersea-features

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