He carried out experiments using kites and balloons, becoming so accomplished that he and his brother set a world record in by flying for 52 hours in a balloon. Wegener first conceived of continental drift in while examining a world map in an atlas, but it took 2 years for him to assemble sufficient data to propose the idea in public. He published the results in book form in He proposed that the similarities between fossils found only in South America and Africa indicated that these two continents were joined at one time.
Although he had marshaled an impressive list of arguments for his hypothesis, he was missing a mechanism. No one could explain how solid continents could drift over thousands of miles. Developing an understanding of the mechanism plate tectonics would take decades of further progress in geology, oceanography, and geophysics.
Wegener was disappointed in the reception of his suggestion, but he continued his research and, in , he was appointed to a special meteorology and geophysics professorship created especially for him at the University of Graz where he was, however, ostracized by most of the geology faculty. Four years later, on his fourth expedition to his beloved Greenland, he celebrated his fiftieth birthday with colleagues and then set off on foot toward a different camp on the island.
He never made it; he was found a few days later, dead of an apparent heart attack. Critics of science often point to the resistance to the continental drift hypothesis as an example of the flawed way that scientists regard new ideas.
Many people who have advanced crackpot theories have claimed that they are being ridiculed unjustly, just as Wegener was. Scientists in his day maintained a skeptical attitude because they needed more evidence and a clear mechanism that would fit what they understood about nature.
Plates pull apart from each other along rift zones, such as the Mid-Atlantic ridge, driven by upwelling currents in the mantle Figure 4. A few rift zones are found on land. The best known is the central African rift—an area where the African continent is slowly breaking apart. Most rift zones, however, are in the oceans. Molten rock rises from below to fill the space between the receding plates; this rock is basaltic lava, the kind of igneous rock that forms most of the ocean basins.
Figure 4. Rift Zone and Subduction Zone: Rift and subduction zones are the regions mostly beneath the oceans where new crust is formed and old crust is destroyed as part of the cycle of plate tectonics. From a knowledge of how the seafloor is spreading, we can calculate the average age of the oceanic crust. About 60, kilometers of active rifts have been identified, with average separation rates of about 4 centimeters per year.
The new area added to Earth each year is about 2 square kilometers, enough to renew the entire oceanic crust in a little more than million years. The present ocean basins thus turn out to be among the youngest features on our planet. As new crust is added to Earth, the old crust must go somewhere.
When two plates come together, one plate is often forced beneath another in what is called a subduction zone Figure 4. In general, the thick continental masses cannot be subducted, but the thinner oceanic plates can be rather readily thrust down into the upper mantle. Often a subduction zone is marked by an ocean trench; a fine example of this type of feature is the deep Japan trench along the coast of Asia.
The subducted plate is forced down into regions of high pressure and temperature, eventually melting several hundred kilometers below the surface. Its material is recycled into a downward-flowing convection current, ultimately balancing the flow of material that rises along rift zones.
The amount of crust destroyed at subduction zones is approximately equal to the amount formed at rift zones. All along the subduction zone, earthquakes and volcanoes mark the death throes of the plate. When the mantle pushes through the crust, volcanoes erupt. At the center of the Earth is the core, which has two parts.
The solid, inner core of iron has a radius of about miles about 1, km , according to NASA. It is surrounded by a liquid, outer core composed of a nickel-iron alloy. The outer core is about 1, miles 2, km thick. The inner core spins at a different speed than the rest of the planet. This is thought to cause Earth's magnetic field. When charged particles from the solar wind collide with air molecules above Earth's magnetic poles, it causes the air molecules to glow, causing the auroras — the northern and southern lights.
To better understand Earth's composition and history, geologists sometimes compare our planet to other rocky planets in our solar system. Venus is a similar size to Earth and a little bit closer to the sun, while Mars is only about half the size of Earth. Although several spacecraft have been sent to Venus and Mars, we know very little about their interiors — yet.
Now, let's answer some commonly asked questions in case you're looking for quick answers. I hope you enjoyed this guide to the layers of the Earth and it sparked a newfound interest in what lies beneath our feet! This is a BETA experience. You may opt-out by clicking here. More From Forbes. Jul 23, , am EDT. Jul 15, , am EDT. Jul 8, , am EDT. Jul 1, , am EDT. Jul 20, , am EDT. Jul 19, , am EDT.
Jul 18, , am EDT. Jul 17, , am EDT. Jul 16, , am EDT. Edit Story. Jan 16, , pm EST. The layers of Earth Credit: www. Follow me on Twitter. Trevor Nace. Diamonds are tiny pieces of the mantle we can actually touch. Most form at depths above kilometers miles. These crystals are then brought to the surface in volcanic rock known as kimberlite.
It behaves more like the crust above it. Together, this uppermost part of the mantle layer and the crust are known as the lithosphere. It is extremely thin, cold and brittle compared to what lies below it. The crust is made of relatively light elements, especially silica, aluminum and oxygen. Under the oceans and Hawaiian Islands , it may be as little as 5 kilometers 3. Beneath the continents, the crust may be 30 to 70 kilometers Along with the upper zone of the mantle, the crust is broken into big pieces, like a gigantic jigsaw puzzle.
These are known as tectonic plates.
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