Plate Tectonics
7th Grade Informational Reading Texts
What portion of Earth makes up the "plates" in plate tectonics? The answer came about in part due to war. In this case, the Cold War. The scientists set up seismometer networks during the 1950s and early 1960s. The purpose was to see if other nations were testing atomic bombs. Since seismometers measure ground shaking, they also recorded earthquakes.
The seismographs located earthquake epicentres. The epicentre is the point on Earth's surface directly above the place where an earthquake occurs.
When earthquake epicentres are put on a map, they outline the plates. This is because the earthquakes where the plates come into contact with each other. Earthquakes are found primarily in lines around the edges of some continents. They are also found through the centres of some oceans. Some occur in patches in some land areas.
If you look at the map pictured below, you will see that the lithosphere is divided into plates. There are a dozen major and several minor plates. Each plate is named for the continent or ocean basin it contains. Some plates are made of all oceanic lithosphere. A few are all continental lithosphere. But most plates are made of a combination of both.
Plates of lithosphere sink into the asthenosphere. The asthenosphere, which is part of the upper mantle, is solid but can flow. If weight is added to a plate, like a glacier, the plate will sink into the mantle. If the weight is taken away, like when the glacier melts, the plate will rise. This happens slowly over long periods of time.
Dividing the lithosphere into plates is one thing. Having the plates move around on the planet is another! A conveyor belt is a good analogy for how a plate moves. How the plates move and where they move is the "tectonics" part of plate tectonics.
Scientists have determined the direction that each plate is moving. Plates move around the Earth's surface at a rate of a few centimetres a year. This is about the same rate that fingernails grow.
Convection within the Earth's mantle causes the plates to move. Mantle material is heated above the core. The hot mantle rises up toward the surface. As the mantle rises, it cools. At the surface, the material moves horizontally away from a mid-ocean ridge crest. The material continues to cool. It sinks back down into the mantle at a deep-sea trench. The material sinks back down to the core. It moves horizontally again, completing a convection cell.
Seafloor spreading takes place as plates move apart from each other at a mid-ocean ridge. Mantle convection drives seafloor spreading.
The theory of plate tectonics is what brings together continental drift and seafloor spreading. Plates are made of lithosphere topped with oceanic and/or continental crust. The plates are moved around on Earth's surface by seafloor spreading. Convection in the mantle drives seafloor spreading. Oceanic crust is created at mid-ocean ridges. The crust moves outward from the ridge over time. The crust may eventually sink into the mantle and be destroyed. If a continent sits on a plate with a mid-ocean ridge, the continent will be pushed along.
Two plates meet at a plate boundary. There are three types of plate boundaries since there are three ways that plates can meet. Plates can move away from each other. They can move toward each other. Finally, they can slide past each other. The three types of plate boundaries are divergent, convergent, and transform. They are described in the following three concepts.
Most geological activity takes place at plate boundaries. This activity includes volcanoes, earthquakes, and mountain building. The activity occurs as plates interact. Giant slabs of lithosphere moving around can create a lot of activity! The features seen at a plate boundary are determined by the direction of plate motion and by the type of crust found at the boundary.
The theory of plate tectonics explains most of the features of Earth's surface. It explains why earthquakes, volcanoes and mountain ranges are where they are. It explains where to find some mineral resources. Plate tectonics is the key that unlocks many of the mysteries of our amazing planet. Plate tectonics theory explains why:
• Earth's geography has changed over time and continues to change today
• Some places are prone to earthquakes while others are not
• Certain regions may have deadly, mild, or no volcanic eruptions
• Mountain ranges are located where they are
• Many ore deposits are located where they are
• Living and fossil species of plants and animals are found where they are
• Some continental margins have a lot of geological activity, and some have none
Plate tectonic motions affect Earth's rock cycle, climate, and the evolution of life.
The seismographs located earthquake epicentres. The epicentre is the point on Earth's surface directly above the place where an earthquake occurs.
When earthquake epicentres are put on a map, they outline the plates. This is because the earthquakes where the plates come into contact with each other. Earthquakes are found primarily in lines around the edges of some continents. They are also found through the centres of some oceans. Some occur in patches in some land areas.
If you look at the map pictured below, you will see that the lithosphere is divided into plates. There are a dozen major and several minor plates. Each plate is named for the continent or ocean basin it contains. Some plates are made of all oceanic lithosphere. A few are all continental lithosphere. But most plates are made of a combination of both.
Plates of lithosphere sink into the asthenosphere. The asthenosphere, which is part of the upper mantle, is solid but can flow. If weight is added to a plate, like a glacier, the plate will sink into the mantle. If the weight is taken away, like when the glacier melts, the plate will rise. This happens slowly over long periods of time.
Dividing the lithosphere into plates is one thing. Having the plates move around on the planet is another! A conveyor belt is a good analogy for how a plate moves. How the plates move and where they move is the "tectonics" part of plate tectonics.
Scientists have determined the direction that each plate is moving. Plates move around the Earth's surface at a rate of a few centimetres a year. This is about the same rate that fingernails grow.
Convection within the Earth's mantle causes the plates to move. Mantle material is heated above the core. The hot mantle rises up toward the surface. As the mantle rises, it cools. At the surface, the material moves horizontally away from a mid-ocean ridge crest. The material continues to cool. It sinks back down into the mantle at a deep-sea trench. The material sinks back down to the core. It moves horizontally again, completing a convection cell.
Seafloor spreading takes place as plates move apart from each other at a mid-ocean ridge. Mantle convection drives seafloor spreading.
The theory of plate tectonics is what brings together continental drift and seafloor spreading. Plates are made of lithosphere topped with oceanic and/or continental crust. The plates are moved around on Earth's surface by seafloor spreading. Convection in the mantle drives seafloor spreading. Oceanic crust is created at mid-ocean ridges. The crust moves outward from the ridge over time. The crust may eventually sink into the mantle and be destroyed. If a continent sits on a plate with a mid-ocean ridge, the continent will be pushed along.
Two plates meet at a plate boundary. There are three types of plate boundaries since there are three ways that plates can meet. Plates can move away from each other. They can move toward each other. Finally, they can slide past each other. The three types of plate boundaries are divergent, convergent, and transform. They are described in the following three concepts.
Most geological activity takes place at plate boundaries. This activity includes volcanoes, earthquakes, and mountain building. The activity occurs as plates interact. Giant slabs of lithosphere moving around can create a lot of activity! The features seen at a plate boundary are determined by the direction of plate motion and by the type of crust found at the boundary.
The theory of plate tectonics explains most of the features of Earth's surface. It explains why earthquakes, volcanoes and mountain ranges are where they are. It explains where to find some mineral resources. Plate tectonics is the key that unlocks many of the mysteries of our amazing planet. Plate tectonics theory explains why:
• Earth's geography has changed over time and continues to change today
• Some places are prone to earthquakes while others are not
• Certain regions may have deadly, mild, or no volcanic eruptions
• Mountain ranges are located where they are
• Many ore deposits are located where they are
• Living and fossil species of plants and animals are found where they are
• Some continental margins have a lot of geological activity, and some have none
Plate tectonic motions affect Earth's rock cycle, climate, and the evolution of life.