Learning objectives. How old is the Earth? What is the Earth made from? What is Plate Tectonics? What happens at the different types of plate boundary?. How old is the Earth?. The Earth is…. 2 million years old. 100 million years old. 4600 million years old. 30 million years old.
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The Earth is…
2 million years old
4600 million years old
30 million years old
Look at this timeline. Where should each statement go?
What do you notice?
First flowers appear – 100 m
India collides with Asia – 50 m
Man (Homo sapiens) inhabits the Earth – 0.1 m
Formation of the Alps – 30 m
You were born! – 0.000013 m
Dinosaur extinction – 65 m
Industrial Revolution (UK) - 0.00015 m
(figures are in ‘million years ago’)
million years ago
People (Homo sapiens) only appeared 100,000 years ago!
Construct your own timeline using the following statements
4.2billion years ago : Continents begin to form
3.7 billion years ago: Earth's crust solidifies
3.5 billion years ago: First life appears in oceans
3.25 billion years ago: Photosynthesis begins in oceans
2.4 billion years ago: Oceans contain significant amounts of oxygen
1.9 billion years ago: First cells with nuclei appear in oceans
0.65 billion years ago: First multicellular organisms appear
0.5 billion years ago: First land plants with inner vessels
245 million years ago: Age of Dinosaurs begins
150 million years ago: Supercontinent breaking up; continents drifting apart
65 million years ago: Age of Dinosaurs ends, with mass extinction of 70% of all living things
3.5 million years ago: First proto-humans appear, in what is now Africa
100,000 years ago: First Homo sapiens appear
10,000 years ago: Recorded human history begins
In 1912, a German scientist called Alfred Wegener proposed that South America and Africa were once joined together and had subsequently moved apart.
He believed that all the continents were once joined together as one big land mass called Pangaea and this was intact until about 200 million years ago.
The idea that continents are slowly shifting their positions is called continental drift.
Evidence for continental drift
Wegener knew the continents had drifted but he couldn't explain how they drifted.
It wasn't until the 1960's that geologists used ocean surveys to explain continental drift with the theory of Plate Tectonics.
Can you name plates A and B?
At a tensional plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface the volcano does not erupt with much force.
Earthquakes are also found at constructive boundaries.
An example of a constructive boundary is the Mid-Atlantic Ridge.
Sea Floor Spreading!
Did you know that the ocean floor in the Atlantic is growing by 3cm per year?
How fast do plates move?
Tectonic plates move at different rates.
The Nazca and Pacific plates are moving apart at a rate of 18cm per year while the Eurasian and North Americanplates are moving apart at a rate of 3cm per year.
To the nearest metre, how far will the Nazca and Pacific plates have moved over the next 200 years?
Where would you find older rocks – at A or at B?
A compressional plate boundary is found where a continental plate meets an oceanic plate.
The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano.
Collision boundaries occur when two plates of similar densities move together (i.e. a continental plate and a continental plate). This causes the material between them to buckle and rise up, forming fold mountains.
The Himalayas are an example of a chain of fold mountains. They have been formed by the Indo-Australian plate colliding into the Eurasian plate.
Passive plate boundaries exist where two plates do not directly collide but slide past each other along a fault (weakness).
No volcanoes are found along these plate boundaries, but earthquakes do occur.
An example of such a boundary is the San Andreas Fault in California.
Match the labels to the letters.
2. The oceanic crust sinks under the less dense continental crust.
3. The oceanic crust melts and rises.
5. explosive volcanoes
4. continental crust