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Hydrosphere- all the waters on the earth's surface, such as lakes and seas, and sometimes including
water over the earth's surface, such as clouds.
Lithosphere- the rigid outer part of the earth, consisting of the crust and upper mantle.
An atmosphere (from Greek meaning "vapour”), meaning "sphere" is a layer of gases surrounding a
planet or other material body, that is held in place by the gravity of that body. An atmosphere is more
likely to be retained if its gravity is high and the atmosphere's temperature is low.
Biosphere- the regions of the surface, atmosphere, and hydrosphere of the earth (or analogous parts of
other planets) occupied by living organisms.
Core: The very center of the earth, very hot but solid. Made up of Nickel and Iron
Mantle: Silicon, Aluminum, Iron, Magnesium, Oxygen, and other elements continually rising, cooling,
sinking, warming up, and rising again.
Crust: The shell forming around the earth, 2 miles thick. Broken into many great “slabs” of rock called
plates that rest/float on the upper portion of the mantle
From the deepest ocean trench to the tallest mountain, plate tectonics explains the features and
movement of Earth's surface in the present and the past.
Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the
mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to
Earth's mantle. This strong outer layer is called the lithosphere.
Developed from the 1950s through the 1970s, plate tectonics is the modern version of continental drift,
a theory first proposed by scientist Alfred Wegener in 1912. Wegener didn't have an explanation for
how continents could move around the planet, but researchers do now. Plate tectonics is the unifying
theory of geology, said Nicholas van der Elst, a seismologist at Columbia University's Lamont-Doherty
Earth Observatory in Palisades, New York.
"Before plate tectonics, people had to come up with explanations of the geologic features in their region
that were unique to that particular region," Van der Elst said. "Plate tectonics unified all these
descriptions and said that you should be able to describe all geologic features as though driven by the
relative motion of these tectonic plates."
The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth's core
rises, and colder mantle rock sinks. "It's kind of like a pot boiling on a stove," Van der Elst said. The
convection drive plates tectonics through a combination of pushing and spreading apart at mid-ocean
ridges and pulling and sinking downward at subduction zones, researchers think. Scientists continue to
study and debate the mechanisms that move the plates.
Mid-ocean ridges are gaps between tectonic plates that mantle the Earth like seams on a baseball. Hot
magma wells up at the ridges, forming new ocean crust and shoving the plates apart. At subduction
zones, two tectonic plates meet and one slides beneath the other back into the mantle, the layer
underneath the crust. The cold, sinking plate pulls the crust behind it downward.
Many spectacular volcanoes are found along subduction zones, such as the "Ring of Fire" that surrounds
the Pacific Ocean.
Continental drift was a theory that explained how continents shift position on Earth's surface. Set forth
in 1912 by Alfred Wegener, a geophysicist and meteorologist, continental drift also explained why lookalike animal and plant fossils, and similar rock formations, are found on different continents.
Wegener thought all the continents were once joined together in an "Urkontinent" before breaking up
and drifting to their current positions. But geologists soundly denounced Wegener's theory of
continental drift after he published the details in a 1915 book called "The Origin of Continents and
Oceans." Part of the opposition was because Wegener didn't have a good model to explain how the
continents moved apart.
Though most of Wegener's observations about fossils and rocks were correct, he was outlandishly
wrong on a couple of key points. For instance, Wegener thought the continents might have plowed
through the ocean crust like icebreakers smashing through ice.
"There's an irony that the key objection to continent drift was that there is no mechanism, and plate
tectonics was accepted without a mechanism," to move the continents, said Henry Frankel, an emeritus
professor at the University of Missouri-Kansas City and author of the four volume "The Continental Drift
Controversy" (Cambridge University Press, 2012).
Although Wegener's "continental drift" theory was discarded, it did introduce the idea of moving
continents to geoscience. And decades later, scientists would confirm some of Wegener's ideas, such as
the past existence of a supercontinent joining all the world's landmasses as one. Pangaea was a
supercontinent that formed roughly 300 million years ago, and was responsible for the fossil and rock
clues that led Wegener to his theory. [Have There Always Been Continents?]
The incredible shrinking plant
When Wegener proposed continental drift, many geologists were contractionists. They thought Earth's
incredible mountains were created because our planet was cooling and shrinking since its formation,
Frankel said. And to account for the identical fossils discovered on continents such as South America and
Africa, scientists invoked ancient land bridges, now vanished beneath the sea.
Researchers argued over the land bridges right up until the plate tectonics theory was developed,
Frankel said. For instance, as geophysicists began to realize that continental rocks were too light to sink
down to the ocean floor, prominent paleontologists instead suggested that the similarities between
fossils had been overestimated, Frankel said.
Plate tectonics is the widely accepted theory that Earth's crust is fractured into rigid, moving plates. In
the 1950s and 1960s, scientists discovered the plate edges through magnetic surveys of the ocean floor
and through the seismic listening networks built to monitor nuclear testing. Alternating patterns of
magnetic anomalies on the ocean floor indicated seafloor spreading, where new plate material is born.
Magnetic minerals aligned in ancient rocks on continents also showed that the continents have shifted
relative to one another.
Abduction Vs. Subduction
Strike Slip Fault