Planet EarthSection 1 What is Earth’s Interior Like? 〉 How is Earth’s interior structured? 〉 Earth’s interior is made up of several distinct compositional

Planet Earth Section 1

What is Earth’s Interior Like?

〉How is Earth’s interior structured?

〉Earth’s interior is made up of several distinct compositional layers.

• crust: the thin and solid outermost layer of Earth above the mantle

• mantle: the layer of rock between Earth’s crust and core


What is Earth’s Interior Like? continued

• Earth’s interior gets warmer with depth.

• Earth’s core is nearly as hot as the surface of the sun.– Earth’s core is composed mainly of nickel and iron.– The inner core is thought to be solid and metal.– The outer core is thought to be made of liquid metal.

• core: the center part of the Earth below the mantle


What is Earth’s Interior Like? continued

• Radioactivity contributes to high internal temperatures.

– The breakdown of radioactive isotopes uranium, thorium and potassium give off energy that contributes to Earth’s high internal temperatures.

– Temperatures in the mantle can reach more than 1250 °C.

– The core may reach temperatures above 5000 °C.


Plate Tectonics

〉How has the appearance of Earth changed over time?

〉Alfred Wegener hypothesized that all of the continents might have been part of one landmass in the past before they drifted apart.

– Wegener pieced the continents together like a puzzle and called the supercontinent they formed Pangaea.

– Wegener found nearly identical fossils on widely separate continents, which supported his idea.


Plate Tectonics, continued

• Evidence for Wegener’s ideas came later.– Wegener’s theory of continental drift was ignored

until structures discovered on the ocean floor provided evidence for a mechanism for the movement of continents.

– Symmetrical bands on either side of a mid-ocean ridge indicate that the two sides of the ridge were moving away from each other and new ocean floor was rising up between them.



• Alignment of oceanic rocks supports the theory of moving plates.– Iron in molten rock aligns itself with Earth’s magnetic

field as it cools.– The Earth’s magnetic field reverses polarity about

every 200,000 years.– The process is recorded as magnetic bands in rock,

based on the age of the rock.– Symmetrical bands on either side of the Mid Atlantic

Ridge suggest that the crust was moving away from the ridge.



• Earth has plates that move over the mantle.– The crust and upper portion of the mantle are divided

into about seven large pieces called tectonic plates.

• lithosphere: the solid outer layer of Earth that consists of the crust and the rigid upper part of the mantle

• plate tectonics: the theory that explains how large pieces of the lithosphere, called plates, move and change shape


Tectonic Plates



• Scientists do not understand exactly what makes tectonic plates move.– One hypothesis suggests that plate movement results

from convection currents in the asthenosphere, the hot, fluid portion of the mantle.

– Another hypothesis suggests that plate movement results from the force of gravity acting on the plates.


Plate Boundaries

〉What geologic features are common near tectonic plate boundaries?

〉Volcanoes and earthquakes most often occur where tectonic plates come together. At plate boundaries, many other dramatic features, such as mountains and rift valleys, can also occur.


Plate Boundaries, continued

• Mid-oceanic ridges result from divergent boundaries.– The border between two tectonic plates is called a

boundary.– A divergent boundary is a place where two tectonic

plates are moving apart.– New rock forms between divergent boundaries.– Magma is liquid rock produced under Earth’s surface.– A rift valley is a narrow valley that forms where

tectonic plates separate.


Divergent Boundaries



• Oceanic plates dive beneath continental plates at convergent boundaries.– Plates slide over each other at a convergent

boundary.– The area where one plate slides over another is

called a subduction zone. Subduction zones produce ocean trenches, mountains, and volcanoes.

• subduction: the process by which one lithospheric plate moves beneath another as a result of tectonic forces


Convergent Boundaries



• Subduction of ocean crust generates volcanoes.– Chains of volcanoes form on the upper plate in a

subduction zone.– These volcanoes can form far inland from their

associated oceanic trench.

• Islands may form where two oceanic plates meet.– Magma rising to the surface may form an island arc.



• Colliding tectonic plates create mountains.– When two plates collide, mountains are formed at the

boundary of the collision.

• Transform fault boundaries can crack Earth.– Plate movement at transform fault boundaries is one

cause of earthquakes.

• fault: a break in a body of rock along which one block slides relative to another

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Planet EarthSection 1 What is Earth’s Interior Like? 〉 How is Earth’s interior structured? 〉 Earth’s interior is made up of several distinct compositional