Plate Movement
>Earth structure, plate tectonics theory: convection currents and sea-floor spreading. Evidence: continental drift and palaeomagnetism. Destructive, constructive and conservative plate margins. Processes: seismicity and vulcanicity
09/06/2014
STRUCTURE OF THE EARTH:
The Earth is made up of the 3 main layers: core, mantle and crust
there is also the lithosphere, continental and oceanic crust, upper mantle, lower mantle, outer core and the inner core
09/06/2014
STRUCTURE OF THE EARTH:
The Earth is made up of the 3 main layers: core, mantle and crust
there is also the lithosphere, continental and oceanic crust, upper mantle, lower mantle, outer core and the inner core
Uppermost layer of mantle and crust = lithosphere
Lower level of mantle is softer and weaker = asthenosphere - thought to be made of peridotite
continental crust = light granitic rock
Oceanic crust = basaltic rock - significantly more dense
crust - 30km
upper mantle - 720km
lower mantle - 2171km
outer core - 2259km
inner core - 1221km
total thickness - 6401km
The earth's crust is also divided into large pieces, called plates. It's unstable because these plates move very slowly. The different plates meets at plate margins, or boundaries. There are four main types of plate margins:
explains how our continents have moved and continue to move across the face of the planet
In the early 1900s when this was first proposed it was greeted with scepticism; it was radical thinking for the time
Permian Period:
The two great land masses of the Paleozoic drifted close enough together to form one supercontinent, Pangaea. Collisions in the tectonic plates created extensive volcanic activity and heaved up the Urals, Alps, Appalachians, and Rocky Mountains. The shallow inland seas drained to leave deposits of gypsum and salt. Vast sand dunes throughout much of what is now North America and Europe were recorded by massive yellow sandstones (hardened sand dunes) that contained few fossils other than scorpions.
Triassic Period:
Early in the Triassic, Pangaea began to break apart again in a process that is still going on. North America, Europe, and Asia split away as one continent (called Laurasia) from South America, Australia, India, Africa, and Antarctica (known as Gondwanaland). These giant continents continued to break apart into the land masses we have today.
Jurassic Period:
During the Jurassic, the supercontinent Pangaea began to break apart. This created two landmasses, a northern mass called Laurasia (North America, Europe, and Asia) and a southern mass called Gondwanaland (South America, Africa, Australia, Antarctica, and India). During the early Jurassic, North America separated from Africa and South America and moved northward, but still remained connected to Europe. By the late Jurassic, the North Atlantic was just beginning to appear between Europe and North America.
Cretaceous Period:
third and last period of the Mesozoic era of geologic time the breakup of the supercontinent of Pangaea became nearly complete. The Atlantic Ocean opened sufficiently so that a substantial body of water existed between North America and Europe and South America and Africa were widely separated. While the Atlantic was opening, the Pacific Ocean continued to close rapidly and an episode of major tectonic change occurred as a result in western North and South America. Specifically, a major subduction zone developed along the western coast of the Americas and substantial tectonic uplift and volcanic activity occurred along this western margin.
Lower level of mantle is softer and weaker = asthenosphere - thought to be made of peridotite
continental crust = light granitic rock
Oceanic crust = basaltic rock - significantly more dense
crust - 30km
upper mantle - 720km
lower mantle - 2171km
outer core - 2259km
inner core - 1221km
total thickness - 6401km
The earth's crust is also divided into large pieces, called plates. It's unstable because these plates move very slowly. The different plates meets at plate margins, or boundaries. There are four main types of plate margins:
- Constructive - where the plates are moving apart
- Conservative - where the plates slide past each other
- Collision - where the plates push against each other often forming mountains - Himalayas
- Destructive - where the plates collide
explains how our continents have moved and continue to move across the face of the planet
In the early 1900s when this was first proposed it was greeted with scepticism; it was radical thinking for the time
Permian Period:
The two great land masses of the Paleozoic drifted close enough together to form one supercontinent, Pangaea. Collisions in the tectonic plates created extensive volcanic activity and heaved up the Urals, Alps, Appalachians, and Rocky Mountains. The shallow inland seas drained to leave deposits of gypsum and salt. Vast sand dunes throughout much of what is now North America and Europe were recorded by massive yellow sandstones (hardened sand dunes) that contained few fossils other than scorpions.
Triassic Period:
Early in the Triassic, Pangaea began to break apart again in a process that is still going on. North America, Europe, and Asia split away as one continent (called Laurasia) from South America, Australia, India, Africa, and Antarctica (known as Gondwanaland). These giant continents continued to break apart into the land masses we have today.
Jurassic Period:
During the Jurassic, the supercontinent Pangaea began to break apart. This created two landmasses, a northern mass called Laurasia (North America, Europe, and Asia) and a southern mass called Gondwanaland (South America, Africa, Australia, Antarctica, and India). During the early Jurassic, North America separated from Africa and South America and moved northward, but still remained connected to Europe. By the late Jurassic, the North Atlantic was just beginning to appear between Europe and North America.
Cretaceous Period:
third and last period of the Mesozoic era of geologic time the breakup of the supercontinent of Pangaea became nearly complete. The Atlantic Ocean opened sufficiently so that a substantial body of water existed between North America and Europe and South America and Africa were widely separated. While the Atlantic was opening, the Pacific Ocean continued to close rapidly and an episode of major tectonic change occurred as a result in western North and South America. Specifically, a major subduction zone developed along the western coast of the Americas and substantial tectonic uplift and volcanic activity occurred along this western margin.
EVIDENCE FOR PLATE TECTONICS
Geology (rocks)
- Broad belts of rocks in Africa and South America are the same type.
- The same three bottoms layers occurred on each of the continents.
- Layers of glacial deposits are found at same place in sequence of rocks on different continents.
Fossils - biological
- Glossopteris flora (plant fossils), an ancient fern, are found in South America, Africa, Antarctica, India, and Australia
- Mesosaurus is a prehistoric aquatic reptile that has been found in rocks both in southern Africa and South America
Seismic activity
- The movement of plates is referred to as continental drift.
It is believed to be caused by heat that in turn creates convection currents in the mantle which "drive" the plates along their path of movement.
- Earthquakes and volcanic activity on the Earth is concentrated in a linear band that snakes around the world, particularly around the edge of the Pacific Ocean where it is known as the Ring of Fire.
- There are mountain ranges being formed where plates are pushing against each other (e.g., the Himalayas, which are still growing).
Under the Ocean
- The ocean basins and sea floor are relatively young. (most less than 150 million years) -
- There are no old oceanic rocks whereas the oldest continental rocks are over 3 billion years old (the oldest continental crust is now known to be 3.96 billion years old)!
- Scientist found that the new rocks being formed had magnetic properties and that polarity changes across the ridge resulting in parallel stripes of reversals on either side. This fact supports the theory of plate tectonics.
Darwin's Evolutionary theory - continental drift
he found that speciation occurred due to continental drift which separated a bird species and they adapted to their environment through survival of the fittest and eventually developed into different types of bird meaning they couldn't breed together.
Geology (rocks)
- Broad belts of rocks in Africa and South America are the same type.
- The same three bottoms layers occurred on each of the continents.
- Layers of glacial deposits are found at same place in sequence of rocks on different continents.
Fossils - biological
- Glossopteris flora (plant fossils), an ancient fern, are found in South America, Africa, Antarctica, India, and Australia
- Mesosaurus is a prehistoric aquatic reptile that has been found in rocks both in southern Africa and South America
Seismic activity
- The movement of plates is referred to as continental drift.
It is believed to be caused by heat that in turn creates convection currents in the mantle which "drive" the plates along their path of movement.
- Earthquakes and volcanic activity on the Earth is concentrated in a linear band that snakes around the world, particularly around the edge of the Pacific Ocean where it is known as the Ring of Fire.
- There are mountain ranges being formed where plates are pushing against each other (e.g., the Himalayas, which are still growing).
Under the Ocean
- The ocean basins and sea floor are relatively young. (most less than 150 million years) -
- There are no old oceanic rocks whereas the oldest continental rocks are over 3 billion years old (the oldest continental crust is now known to be 3.96 billion years old)!
- Scientist found that the new rocks being formed had magnetic properties and that polarity changes across the ridge resulting in parallel stripes of reversals on either side. This fact supports the theory of plate tectonics.
Darwin's Evolutionary theory - continental drift
he found that speciation occurred due to continental drift which separated a bird species and they adapted to their environment through survival of the fittest and eventually developed into different types of bird meaning they couldn't breed together.
Vulcanicity
Types of Lava |