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Science of the Earth
Transcript of Science of the Earth
Science Of The Earth
Layers of the
Sea-floor spreading is when the ocean floor is extended by two tectonic plates move away from each other (diverging). This is due to plate tectonics and divergent plates of the earth.
According to plate tectonics theory, Earth is divided into large plates that can move and shift. These plates can move away from each other, smash into each other or grind past each other. No single plate can move without affecting others. The size and position of these plates change over time. The edges of these plates, where they interact are places of intense geologic activity, such as earthquakes, volcanoes, and mountain being formed.
Convection currents occur in the asthenosphere because of extremely hot material at the bottom of the mantle rises and cooler materials at the top of the mantle sink to the bottom and the process repeats.
These convection currents are huge in plate tectonics because the cause the plates to shift. The plates float on top of the liquid layer of the mantle. The currents cause the plates to converge, diverge and become transform faults.
The crust is earths thin, outer, rocky layer. The crust ranges from about 3-25 miles thick. It's rich with granite and basalt. Relative to its size, Earth's crust is about as thin as an apple's skin. This is the layer we live on.
The earth is made up of 3 primary layers
The next layer is the mantle, the upper mantle (which contains some of the Lithosphere and the asthenosphere) and the lower mantle. The Upper Mantel is made up of silicates of iron and magnesium. It is firm on top (lithosphere) with liquid rock on the bottom (asthenosphere). The lithosphere floats on the lower, liquid mineral part of the Upper Mantle (the asthenosphere). The whole mantle is about 1,800 miles thick.
The lithosphere is the rigid rocky layer of the earth including the crust and part of the upper mantle
Earth has two parts of its core, the outer core and the inner core. Starting with the outer core, the outer core is located around 1800 miles under the crust and is about 1400 miles thick, its temperatures range from 4000-8000 degrees Fahrenheit it is liquid. The outer core is composed of the melted metals nickel and iron. Next is the inner core, The inner core is solid (because of pressure) starts about 4000 miles under the crust. It is about 800 miles thick and is made of iron and nickel also. The temperatures may reach 9000 degrees F. and the pressures are 45,000,000 pounds per square inch.
In the 1900's German meteorologist Alfred Wegener was the first to present the idea of continental drift. Wegener noticed that the continents seemed to fit together, not at the always changing shoreline, but at the edge to their continental shelves. He suggested that at one point in time all of the continents formed one "super-continent" called Pangea
The first piece of evidence that supports the theory of continental drift is the fit of the continents depicted in the pictures below.
Secondly, another piece of evidence of continental drift is similar fossils found across continents. Ancient marine reptile, Mesosaurus,fossils have been found exclusively on the west coast of South America and the southern east coast of Africa along with similar plant fossils.
A third piece of evidence is rock and structures. Similar and the same types of rock structures and sequences such as faults and folds have been found across two different continents . When the continents moved the structures were split
Lastly, there is Paleoclimatic evidence of continental drift. Evidence from glacial movement can be deciphered from grooves discovered in specific rocks. Grooves from ancient glacial movement have been recorded on all the southern coasts of Australia, India Africa and South America
Evidence of Sea-floor spreading
Firstly, the rock making up the ocean floor is much younger than the age of the continents it's connected with, with no samples found over 200 million years old, it is considerably younger than the 3 billion year old samples found for continental rocks. This confirms that older ocean crust has been reabsorbed in ocean trench systems.
Secondly, Earth has a tenancy to flip its polarity about every 200,000 years which means that the magnetic north, the way a compass points, would point to the magnetic south. When scientists plotted the points of normal and reversed polarity on a seafloor map they made an amazing discovery. The normal and reversed magnetic polarity of seafloor basalts creates a pattern. The sea floor age and spreading directly correlates with earths flipped polarity. Scientists can measure this with a magnetometer, a device used to measure the intensity or direction of a magnetic field.
Divergent plate boundaries
Convergent plate boundaries
Transform-fault plate boundaries
Divergent plates creates new crust as one more plates move away from each other. When they pull away from each other, magma from the mantle rises to the top and hardens, creating new crust. Oceans are born or grow larger because of divergent plates. This type of boundary is the cause of sea-floor spreading. Scientists are studying this type of boundary in Iceland on the mid-Atlantic ridge.
Convergent plates are essentially the opposite of divergent plates. With convergent plates, crust is destroyed and recycled back into the earth. When two plates crash into each other one and one dives under the other. Where one plate dives under the other is called a subduction zone. Many volcanoes and mountians are found where plates converge. There are 3 types of convergent boundaries: Oceanic-Continental Convergence; Oceanic-Oceanic Convergence; and Continental-Continental Convergence.
Transform plate boundaries are where plates are sliding past each other horizontally other than it being two plates moving it is not very similar to the other two types of boundaries. This boundary is often referred to as a fault. Most transform boundaries are found on the ocean floor. However some, like the San Andreas fault in California is one of the few transform faults that occurs on land. The fault causes earthquakes in California.
Volcanoes are an opening in the earth's crust from which molten lava, rock fragments, ashes, dust, and gases are ejected from below the earth's surface. Volcanoes are initially created at convergent plate boundaries. When the two plates converge, one plate sinks below the other one. From there the plate that sank melts in the mantle, the heat pressure forces the now lava up in the mountain formed by the converging plates of a volcano. There are many parts that make up a volcano
Shield volcanoes are large volcanic structures with long gentle slopes built up almost entirely from fluid lava flows.the shape of this type of volcano is more like a dome than a tall cone. This type of volcano is built slowly and can have multiple vents producing lava flows. and lava flows up in the outer parts of the volcano giving it the look of a warriors shield if cut in half. Thus the name "shield volcano"
Cinder cone volcanoes are the simplest volcano. These volcanoes have a cone shape built by an accumulation of loose bits of magma called "scoria" that fall around a vent or crater after being expelled during moderately explosive activity.
The " Pacific Ring of Fire" is an arc reaching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. The Ring of Fire is composed over 75% of the world's active and dormant volcanoes!
Anatomy of a volcano
Composite volcanoes, also known as a stratovolcano. This is the most stereotypical volcano. It is a cone shaped mountain with steep, barren slopes often with a single plume of smoke coming from a single central vent (opening in the earths surface from which volcanic materials can come from). It is composed of alternating layers or "strata" of material created by pyroclastic (lava) flows. Liquid magma is emitted from a reservoir deep in the earth's crust.
Along with volcanoes there are certain other volcanic-type geological formations such as: batholiths, laccoliths.
A batholith is a large mass of intruded igneous rock that is stopped in its rise a considerable distance below the surface. Batholiths cut through original bedrock and have vertical walls. Batholiths can both be solid or in liquid form.
A crater is the bowl shaped feature at the top of a volcano. Through explosive,volcanic activity, this crater can be enlarged and the top of the volcano collapses on its self, this is called a caldera
The vent is simply the opening in the earths crust that allows magma and other volcanic gases to escape. it is the main part of a volcano
Dikes are the veins of a volcano, the pathways of rising magma. A dike is usually vertical. Dikes are straw-like magma bodies that cut through older rocks or sediments.
Sills are very much like dikes, but, instead of being vertical, they are commonly horizontal. The main difference between dikes and sills are that sills store magma while dikes transport magma.
There are 3 main types of volcanoes
A laccolith is very similar to a batholith except laccoliths are much smaller without vertical walls that cut across the original bedrock. Also, laccoliths stop from reaching the surface and then spread laterally creating a bulge in the crust. In addition, laccoliths tend to be much shallower than batholiths.
Silicas importance in magma
The higher the silica content of the magma in a volcano, the more explosive the eruption will be. This is because magma enriched with silica has a higher viscosity (resistance to flow). Pressures are more likely to build up behind the thicker, high silica content magma and result in potentially more explosive eruptions. Water vapor is also present in magma, the more water vapor in the silica, the more explosive eruption.
Intrusive igneous features
Volcanoes can also be formed through "intrusive igneous" processes. This is where magma finds its way to the surface, from a batholith or pluton, of the earth through the crust. when the magma cools it creates a mound that builds and builds with every time that magma reaches the surface and cools then hardens. This process repeats many times to finally form a volcano.