Science 7: Unit E: Planet Earth Topic 4 – The Moving Crust

What makes a good Scientific Theory? Two things: Two things: I. It can explain why something in the universe is the way it is, acts the way it does, etc. I. It can explain why something in the universe is the way it is, acts the way it does, etc. II. It can make a testable prediction about some yet untested question. II. It can make a testable prediction about some yet untested question. Eg. I can explain that decomposers are necessary for an ecosystem, but unless I can make a testable prediction (an ecosystem with the decomposers removed will become full of waste and dead organisms) it is useless. Eg. I can explain that decomposers are necessary for an ecosystem, but unless I can make a testable prediction (an ecosystem with the decomposers removed will become full of waste and dead organisms) it is useless.

The Structure of the Earth From outside to centre: From outside to centre: I. Crust – 5-60 km thick: This is the rocky outside of the Earth where all organisms live. We’ve never seen anything but the crust. I. Crust – 5-60 km thick: This is the rocky outside of the Earth where all organisms live. We’ve never seen anything but the crust. II. Mantle – 2885 km thick: Rock and magma under the crust. Temperatures range from C. II. Mantle – 2885 km thick: Rock and magma under the crust. Temperatures range from C. III. Outer Core – 2270 km thick: Liquid iron and nickel. Temperatures here are 5500C. III. Outer Core – 2270 km thick: Liquid iron and nickel. Temperatures here are 5500C. IV. Inner Core – 1216 km thick. Even though temperatures here are higher than in the outer core (6000C), the pressure of the weight of the Earth keeps the metal (iron and nickel) a solid ball. IV. Inner Core – 1216 km thick. Even though temperatures here are higher than in the outer core (6000C), the pressure of the weight of the Earth keeps the metal (iron and nickel) a solid ball. NOTE: Lithosphere – The rocky part of the Earth (upper Mantle and the Crust). NOTE: Lithosphere – The rocky part of the Earth (upper Mantle and the Crust).

Why is the Earth arranged the way it is? In 1910, Alfred Wegener noticed that the continents had shapes that fit together like pieces in a jigsaw puzzle. Based on this he made his theory: In 1910, Alfred Wegener noticed that the continents had shapes that fit together like pieces in a jigsaw puzzle. Based on this he made his theory: Continental Drift Theory: It is hypothesized that the continents were at one time part of a single super-continent called Pangaea. They then drifted apart. They continue to drift today. Continental Drift Theory: It is hypothesized that the continents were at one time part of a single super-continent called Pangaea. They then drifted apart. They continue to drift today.

Evidence for Continental Drift Theory To support his theory, Wegener collected the following evidence: To support his theory, Wegener collected the following evidence: Continents’ edges fitting together. Continents’ edges fitting together. Similar mountain and land formations in different continents. Similar mountain and land formations in different continents. Fossils of similar species of animals and plants in different continents, even Antarctica. Fossils of similar species of animals and plants in different continents, even Antarctica. In the end, Wegener could not explain WHY the continents were moving and so his theory was not taken seriously. In the end, Wegener could not explain WHY the continents were moving and so his theory was not taken seriously.

Advances in Technology Since Wegener, society has developed new technology that has helped map the ocean floor and provided new clues about Earth’s interior (which can’t be seen directly), tech. such as: Since Wegener, society has developed new technology that has helped map the ocean floor and provided new clues about Earth’s interior (which can’t be seen directly), tech. such as: Sonar – Sound waves emitted by a ship or sub bounce off the ocean floor and help give the distance and shape of the floor. Sonar – Sound waves emitted by a ship or sub bounce off the ocean floor and help give the distance and shape of the floor. Deep Sea Subs – scientists can travel and observe ocean trenches and ridges directly in the safety of their vehicle. Deep Sea Subs – scientists can travel and observe ocean trenches and ridges directly in the safety of their vehicle.

Sea Floor Spreading Theory With the new information provided by sonar, deep sea vehicles and magnetic readings near the Mid-Atlantic Ridge, scientists noted that the evidence pointed to a sea floor in the Atlantic that was creating new rock. With the new information provided by sonar, deep sea vehicles and magnetic readings near the Mid-Atlantic Ridge, scientists noted that the evidence pointed to a sea floor in the Atlantic that was creating new rock. Sea Floor Spreading Theory – Because of the creation of new igneous rock at the Mid-Atlantic Ridge, the sea floor is continuously spreading. Sea Floor Spreading Theory – Because of the creation of new igneous rock at the Mid-Atlantic Ridge, the sea floor is continuously spreading. This theory was a step in the right direction, but it couldn’t explain everything. That would come with the next theory. This theory was a step in the right direction, but it couldn’t explain everything. That would come with the next theory.

Theory of Plate Tectonics Based on all of the collected evidence, scientists have created a new theory that explains all of the evidence so far and makes predictions about what areas of the Earth are likely to have volcanoes and earthquakes. Based on all of the collected evidence, scientists have created a new theory that explains all of the evidence so far and makes predictions about what areas of the Earth are likely to have volcanoes and earthquakes. Theory of Plate Tectonics - the Earth’s crust is actually broken up into pieces called plates which float on the magma mantle. Plates moving towards each other are called converging plates, plates moving away are called diverging plates, and plates sliding past each other are called shearing plates. Theory of Plate Tectonics - the Earth’s crust is actually broken up into pieces called plates which float on the magma mantle. Plates moving towards each other are called converging plates, plates moving away are called diverging plates, and plates sliding past each other are called shearing plates. The plates are usually named after the continents they contain. The plates are usually named after the continents they contain.

Diverging Boundary The boundary between two diverging plates. Eg. Iceland near the Mid-Atlantic Ridge. The boundary between two diverging plates. Eg. Iceland near the Mid-Atlantic Ridge. This area is characterized by volcanic eruptions and earthquake activity. This area is characterized by volcanic eruptions and earthquake activity. The diverging boundaries are caused by convection currents in the magma pushing warmer magma up, until the pressure causes an eruption (most of the time it cools enough and sinks back down.) The diverging boundaries are caused by convection currents in the magma pushing warmer magma up, until the pressure causes an eruption (most of the time it cools enough and sinks back down.) Diverging boundaries will eventually form ridges like the Mid-Atlantic Ridge. Diverging boundaries will eventually form ridges like the Mid-Atlantic Ridge.

Converging Boundary The boundary between two converging plates. Eg. The Himalayas. The boundary between two converging plates. Eg. The Himalayas. These areas are characterized by high mountain ranges, earthquakes, and the occasional volcano. These areas are characterized by high mountain ranges, earthquakes, and the occasional volcano. If a continental tectonic plate (lighter and thicker) bumps into an ocean plate (heavier and thinner), the ocean plate will slide under the continental plate and become magma, while the continental plate will rise and form mountains. If a continental tectonic plate (lighter and thicker) bumps into an ocean plate (heavier and thinner), the ocean plate will slide under the continental plate and become magma, while the continental plate will rise and form mountains. This process of one plate sliding under the other is called subduction. This process of one plate sliding under the other is called subduction.

Converging Boundaries Cont’d If two continental plates collide, you’ll get mountains. If two continental plates collide, you’ll get mountains. If a continental and oceanic plate collide, you’ll get subduction and mountains volcanoes. If a continental and oceanic plate collide, you’ll get subduction and mountains volcanoes. If two oceanic plates collide, you’ll get islands and a deep ocean trench. If two oceanic plates collide, you’ll get islands and a deep ocean trench.