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for Plate Tectonics – GEOetc
The evidence for Plate Tectonics is very conclusive. It is a very well supported theory, and while scientific debate continues about small parts or local effects, the overall concept is accepted as good as fact.
So what are the pieces of evidence?
Shape of continents
From almost the creation of the first true maps of the Earth, people started seeing how continents would be able to fit together. In particular, people noticed that South America fits almost exactly into Africa.
You should be aware that while world maps were around early in the 1600’s and better defined by the end of the 1700’s, those maps were not ‘public’ but were treated as state secrets. And so it was not till much later that the broader ‘science’ community had access to good quality and accurate world maps.
It is now known that most of the major continental masses can be fit together in a jigsaw process. In fact, we now know that the continents were indeed once all joined together as one landmass – the supercontinent of Pangaea.
If you look at most world maps you will ponder how this is evidence, as the continents really don’t appear to ‘fit’ together very well. What you need to understand is that the vast majority of maps are drawn using a map projection that has the north and south poles (which are points) are a line the width of the map at the top and bottom. This means that the map distorts the true shape of the Earth’s land and oceans as you love closer to the poles. Some other map projections distort less, but have the map shape looking like segments of an orange. See here for a range of map projections. Check out the way Greenland changes size in each!
What is more remarkable, is the next piece of evidence when added to the shape of continents.
Location of mountains and fossils
What is remarkable, when you reassemble all the continents together, the ancient mountain ranges (many now eroded to their cores) and the location of rock types and fossils all match up.
Earthquakes and Volcanoes
As you can imagine, if plates that are made up of huge slabs of rock are grinding past or under each other, then those would be the places where the vast majority of earthquakes would take place. If we map the location of all the earthquakes recorded over time, almost all of them occur along what we recognize as plate boundaries.
Likewise, the exception of special volcanoes called hot spots (see below), all of the active volcanoes on Earth are found on some of the boundaries between plates.
In this diagram, we see the Aleutian area off North America. The black dots and circles represent recorded earthquakes. You can see they form a zone. Look above and below the zone, and there are almost none. So the earthquakes define the boundary. Not only that, they show that earthquakes are shallow in depth on the southern side of the zone getting deeper and deeper as you go northwards. This is because the Pacific Plate to the south is being forced under the North American Plate in the north. As it is forced under it is getting deeper and deeper until it finally melts into the underlying mantle.
The red triangles are active volcanoes. They also follow the earthquake pattern but are found on the far side of the zone, along with the deep earthquakes.
Hot Spot Volcanoes
Deep in the Earth, possibly at the boundary between the outer crust and the mantle, some form of disturbance funnels vast heat up towards the Earth’s surface in places we call Hot Spots. These Hot Spots are localized intense zones that can melt the overlying crust and form a volcano.
Because the Hot Spot is completely independent of what is happening with the crust, the resulting volcanoes are not related to the position of the plates. So many hot spot volcanoes occur nowhere near a boundary.
But what is more significant is that when the plate moves away from the hotspot, the hot spot volcano no longer has the heat and becomes extinct. The new area of plate above the hot spot then melts and a new volcano is formed. So we end up with a chain of volcanoes, the active volcano over the hotspot and the remains of volcanoes getting older and older as you move away from the hot spot.
The Hawaiian Islands are an example of this hot spot phenomenon. The most active volcano, Kilauea, is above the hotspot, and the volcanoes moving north-west get older and older. The largest of these still stick out of the ocean, but many more remnants of volcanoes that are now further away from the hot spot and most are under the ocean surface.
Because we know the age of the rocks on each of these old volcanoes, and we know how far away they are from the hot spot, we can calculate how fast the crustal plate is moving over the hotspot. In Hawaii’s case, the Pacific Plate on which the island sit is moving towards the north-west at around 10 cm a year.
Check out the STEM on an Active Volcanoes resource (video, teacher notes and classroom activities)
Other hotspots exist around the globe which can give us the speeds of other plates.
Get a FREE plate tectonics activity called “Rocks of Ages”. Your students will be calculating the speed of the Pacific plate as it moves over the Hawaiian Hotspot.
Go here to get the activity.
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For more of our blogs on Plate Tectonics see these posts:
Structure of Earth
Have your students summarize the basic structure of the Earth – crust, mantle, outer core, and inner core – on …
Rocks of Ages
Description : Student activity where they calculate the speed of a moving tectonic plate by using the ages of rocks …
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Evidence for Plate Tectonics – GEOetc
What is the Evidence for the Theory of Plate Tectonics?
Frequently Asked Questions About evidence that supports the theory of plate tectonics
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What are the five proofs for the plate tectonics theory?
Continental drift, the appearance of younger crustal layers in the ocean, earthquakes along plate boundaries known as fault lines, the presence of similar fossils and rocks on different continents, and the similar shapes of continents that once fit together as a larger continent are all evidence for the theory of plate tectonics.
What proof does the quizlet’s plate tectonics theory provide?
The age of the rocks that make up the ocean’s crust, coral islands, the location of ocean trenches, and the sites of earthquakes and volcanoes are the five main pieces of evidence for the Theory of Plate Tectonics.
Which four major lines of evidence support plate tectonics?
They used a variety of pieces of evidence to support their theory of continental drift, including the fit of the continents, paleoclimate indicators, truncated geologic features, and fossils.
What is the most convincing proof of plate tectonics?
Seafloor spreading is the mechanism causing the magnetic material in the seafloor to alternate between stripes with magnetic material oriented toward magnetic north, and those with magnetic material oriented in the opposite direction, providing strong evidence for tectonic theory.
Which three theories of plate tectonics are there?
Divergent plate boundaries mean that the two plates are moving apart, whereas converging plate boundaries mean that they are moving together, and transform plate boundaries mean that they are moving past one another.
What two theories aid in the understanding of plate tectonics?
Actually, continental drift and seafloor spreading are combined into one comprehensive global theory called plate tectonics.