Tunnel from Chicago through the center of the Earth and you’d pop up in the middle of the Indian Ocean off the coast of Australia. Note that the maps are at different scales for context. Credit: Aniotek Solutions
Ever wonder what’s on the opposite side of the planet from where you live? China maybe? Nothing could be further from the truth. Instead, you’d be splashing about in the Indian Ocean off the west coast of Australia. Places on the globe that are diametrically opposite one another are called “antipodes.” If you draw a straight line from your town directly through the center of the Earth, it will emerge at its antipode.
I came across a fun, interactive antipodes map the other day. Type in your city name, tap enter and you’ll see a little guy with his head stuck in the ground in your town and his face smiling back from the antipode. Or you can scroll around the planet with your mouse, zooming in and out and picking favorite cities. The entire mainland U.S. lies exactly opposite the Indian Ocean west and south of Australia, but if you go to Maui in Hawaii and dig a very deep hole, your head will pop out in the middle of Botswana in Africa.
And the proverbial China? Head down to Chile or Argentina and get diggin’! It’s easy to imagine boring a hole through the planet but ultimately an impossible task. Much easier to focus on flying to the stars. To date, the deepest hole ever drilled into Earth’s belly is the Kola Superdeep Borehole in the Kola Peninsula in Russia. It’s 9 inches across and 7.5 miles (12,261 meters) deep in granite rock. Engineers began drilling in 1970 and continued on and off for 24 years.
The project came to an end in the early 1990s when higher than expected temperatures were encountered: 356°F (180°C) at hole bottom! The rock there was unexpectedly porous. Worked over by the heat and high pressure at that depth, it became more plastic, making it impossible for the drill to continue. The site was closed in 2006 after funding dried up, then abandoned two years later. It looks vandalized now — a pity. Scientists studying the rock made some surprising discoveries, including finding fossilized plankton 4.3 miles beneath the surface and water. Not water trickling down from above but water formed from hydrogen and oxygen squeezed out of the rocks under pressure.
Researchers estimate the drill penetrated only about a third of the way through the Earth’s outermost layer, the crust, at the Kola location. The Kola Superdeep Borehole Project barely made a dent, reaching only 0.2% to Earth’s core. What would happen if we really tried to get to an antipode? Well, we’d have to burrow through through the crust first which varies in depth from 3.1 to 43.5 miles (5-70 km).
The temperature keeps rising as you go down at the rate of about 1 for every 70 feet. Much of the heat comes from the decay of natural radioactive elements, but heat from the force and compression created by meteorite and asteroid impacts 4.5 billion years ago is still around, too. Lunar tides heat the interior, and the slow trickle of metal squeezed from rock dribbling to the core also warms the surrounding rock.
Earth’s interior is divided into three spherical shells: the brittle crust, the dense, plastic mantle and a metallic core. The mantle’s the thickest layer averaging about 1,800 miles (2,900 km) in depth with temperatures from 932 to 1,652°F (500-900°C ) at the upper boundary to over 7,200°F (4,000°C) at the boundary with the core. Mantle material is so hot it behaves more like thick molasses; the crust “floats” atop the mantle, riding slow-churning swells of gooey rock.
1,800 miles (2,900 km) below your feet, you’d reach the outer, molten core, where the temperature sizzles from 8,000° F (4,400° C) to 11,000° F (6,093°C), as hot as the surface of the sun. Currents in the iron-nickel metal that comprises the core are believed responsible for creating Earth’s magnetic field that does everything from orienting our compass needles to protecting us from atmosphere-stripping winds from the sun.
After another 700 miles (1,150 km), we’ve finally arrived at the inner core, a solid ball of iron-nickel 70% the size of the moon slow-roasting at 9,750° F (5,400° C). The inner core is believed to be growing at the rate of about 1 mm per year as molten iron bordering the inner and outer cores slowly crystallizes. When crystals form, heat is released which rises up through the mantle, providing yet another source for the what keeps our planet warm.
After our crushing, blistering journey, we head back up and out the antipode, which for my city lies in the cool, blue Indian Ocean.
How do we know all this stuff without going any deeper than 7.5 miles? Our knowledge of Earth’s interior comes from seismic waves released during earthquakes and volcanic eruptions that reflect and refract through the planet, carrying information back to detectors. Scientists interpret them much like a bat “sees” its environment by sending out high-frequency sound waves and interpreting their echoes.
Some of you might remember the old sci-fi movie, Journey to the Center of the Earth, where Prof. Lindenbrook (James Mason) and company reach the center of the Earth through an extinct volcano in Iceland. There they discover a subterranean ocean, dinosaurs and even the sunken city of Atlantis. I remember being mesmerized by this as a kid. Now in 2017, I find the science just as thought-provoking.