The slip of tectonic plates and the fiery eruptions of volcanoes are just the surface manifestations of the beating heart of our planet. Earth is composed of layers, each one playing a different role in protecting all life from solar storms, recycling the planet's crust and even changing our climate. The ground beneath our feet is a dynamic place that affects us every day.
We may marvel at mountains that tower above our heads or hold our breath when confronted with dizzying views of canyons, but none of that would be possible without the inner Earth. Join us as we peel back the layers of our planet, exploring what scientists know about our world and what mysteries remain.
Scroll down for a tour through the depths of the earth, by David Whitehouse, author of Into the Heart of Our World...
Mile 2.5: World's deepest mine "At Mponeng mine every day 4,000 workers descend into an underground city and it is like working in an oven. In the depths of the mine the rock is at 140°F, too hot to touch."
"The deepest hole ever made was a Soviet initiative in 1983 to drill through the crust to the mantle. It reached 7.5 miles, a third of the required distance." The opening to the Kola Superdeep Borehole is now welded shut.
"The boundary between the light crust and the denser mantle, called the Moho discontinuity, is between 3 and 6 miles below the ocean floor, and 12 to 55 miles below the continents.
In the past, the mantle--Earth's thickest layer at 1800 miles thick, making up and 84% of the earth's volume--was regarded as a bland, featureless region, just a layer of rock between the crust and the core in which rock moved very slowly. Recent discoveries have shown it to be an active region transporting material to and from the surface."
These rocks were formed near the Moho discontinuity and are now exposed at the surface in Newfoundland.
"Diamonds are nature's hardest substance and are formed when carbon is subjected to intense heat and pressure for between 1 and 3.3 billion years, usually between 86.9 – 118 miles in the mantle."
"Most earthquakes occur at depths of less than 186 miles. Below that depth the rock is plastic and deforms slowly instead of in jumps. There are 900,000 quakes a year, mostly too small to be felt. But each year on average there are twenty quakes that cause serious damage and every few years a great one strikes."
"Major changes to rock structure occurs in the mantle at depths of 273 and 410 miles. The changes form the earth's most common rock -Bridgmanite - named after pioneering scientist Percy Bridgman who subjected rocks to great pressure to simulate conditions inside the earth."
"Ultra-Deep diamonds, formed at 416 miles deep, are rarer than moon rocks. Fewer than a dozen ultra-deep diamonds have been found."
"Rising 310–620 miles above the core-mantle boundary are two giant structures, each 9,300 miles across. They are called Tuzo and Jason and are our planet’s underground continents. Recent research suggests they are ancient and are likely to have formed 4.4 billion years ago when the Earth was young."
"The Core Mantle Boundary, says Prof Ed Garnero of Arizona State University, is one of the strangest and most significant places in Earth. It contains what could be termed the Earth’s 'Dark Matter.'"
"The outer core is made of molten iron, nickel and a few other elements at a pressure of 3.3 million atmospheres. It profoundly affects the nature of our planet and the magnetic field it generates protects us from the harshness of the cosmos." This iron meteorite slice is similar in composition to the earth's outer (and inner) core.
"Small as it may be, with a radius of 750 miles and a surface area equal to that of Antarctica, the solid iron inner core, at a pressure of 3 million atmospheres, packs more strangeness and mystery into its volume than any other region of the Earth."