Union Park geotechnical drilling crews often receive questions concerning precisely what’s underground. In fact, most are unfamiliar with the different layers that comprise the ground beneath our feet.
So let’s take a look at the earth’s layers, how they differ and what layer(s) you can expect to encounter while performing geotechnical drilling. Union Park natives often ask about what layers are involved in a drilling project and what comprises those layers.
Union Park geotechnical drilling crews focus on the very outermost layer, called the earth’s crust. It’s the thinnest layer which can range from 5 to 25 miles thick on land and as little as 3 to 5 miles thick in the regions beneath the oceans. It’s comprised primarily of basalt and granite.
At the deepest points of the crust, the temperatures raise to 1,600 degrees Fahrenheit. Drilling operations never go below this level. This is due to the heat and pressures encountered at deeper levels, combined with the challenging logistics of operating drilling equipment that extends miles underground!
Beneath the earth’s crust is the mantle, which is comprised of soft, hot stone that moves in a manner similar to hot asphalt. This layer is about 1,800 miles thick. It can range in temperature from 1,600 degrees Fahrenheit to 4,000 degrees Fahrenheit, with the temperatures getting hotter the deeper you go. It’s believed that the hot stone moves in “convection currents.”
Below the mantle is the outer core, which is comprised of liquid metals like iron and nickel. The temperatures range from 4,000 degrees Fahrenheit to 9,000 degrees Fahrenheit. The outer core is about 1400 miles thick.
At the very center of the earth is the core, with extreme temperatures of 9,000 degrees Fahrenheit or hotter. The core begins at a depth of 4,000 miles below the earth’s crust and it has a diameter of approximately 760 miles. For comparison, the inner core is about 7/10 the size of the moon.
Due to the extreme pressures at the earth’s core, the metals cannot move as a liquid so they’re in a state that’s more like a solid. The pressures are estimated to be 45 million pounds per square inch – that’s 3 million times the pressure you experience at sea level. If you could travel to this depth, you would be compressed to the size of a marble or smaller by the extreme pressures.
Scientists are not certain of the composition, but it’s believed the inner core is comprised of a nickel-iron alloy.
Of course you’ll never reach this depth when performing geotechnical drilling. Union Park drilling projects will only ever go into the very upper portion of the crust. One drilling team in the Indian Ocean did try to drill into the mantle in early 2016, but they were unable to reach this layer. They did drill the deepest “single leg” hole into hard rock by reaching a depth of 789 meters and their drill hole was the fifth deepest ever drilled into the crust under the ocean.