Earth History and Plate Tectonics

Most scientists believe that the Earth and our solar system formed about...

• 13.8 billion years ago

• 4.6 billion years ago

• 600 million years ago

• 10,000 years ago

Answer explanation

The moon formed when another small planet crashed into the Earth and sent lots of debris into orbit.

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Earth history

Which of these is the earliest eon in Earth's history?

• Palaeozoic

• Phanerozoic

• Archean

• Hadean

Answer explanation

The Hadean is named after Hades, god of the underworld, because the Earth's surface would have been 'hellish' - molten rock with frequent asteroid strikes.

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Earth history

The Earth's structure is made up of several different layers. Which of the following layers is the thinnest?

• crust

• mantle

• outer core

• inner core

Answer explanation

The crust averages 33km thick under the continents and just 7km thick under the oceans. That is just 0.02% of the thickness of the planet!

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Earth structure

Which of the Earth's layers is a liquid?

• crust

• mantle

• outer core

• inner core

Answer explanation

Although the inner core is the hottest part of the Earth, the pressure is so high it remains a solid.

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Earth structure

The Earth's structure is made up of several different layers. Which of the following layers is the thickest?

• crust

• mantle

• outer core

• inner core

Answer explanation

The mantle is the thickest layer but it is often divided into different parts because it behaves very differently at different depths.

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Earth structure

What is the composition of the Earth's inner core?

• silica

• iron and nickel

• magnesium

• carbon

Answer explanation

The inner and outer core have the same composition but they are considered as different layers as one is solid while the other is a liquid.

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Earth structure

Which of these features are true for continental crust?

• silica-rich granitic rocks

• iron-rich basaltic rocks

• 5-10km thick

• 20-70km thick

Answer explanation

Some continental crust is almost as old as the Earth itself - zircon crystals in the rocks have been dated as 4.4 billion years old.

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Cont and ocean crust

Which of these features are true for continental crust?

• more dense than oceanic crust

• less dense than oceanic crust

• older than oceanic crust

• younger than oceanic crust

Answer explanation

The continental crust is less dense because the rocks contain less iron than the oceanic crust.

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Cont and ocean crust

Which type of plate boundary causes oceanic crust to subduct into the mantle?

• divergent (moving apart)

• convergent (moving towards each other)

• conservative (moving past each other)

• divergent and convergent (apart and towards)

Answer explanation

Subduct comes from two Latin words - 'sub' meaning 'under' and 'duct' meaning 'to flow'.

Tags

plate boundaries

Which type of plate boundary are volcanoes found close to?

• divergent (moving apart)

• convergent (moving towards each other)

• conservative (moving past each other)

• divergent and convergent (apart and towards)

Answer explanation

Volcanoes are formed when rocks in the upper mantle melt - this usually happens due to a change in pressure or when water is added.

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plate boundaries