The Earth’s Interior

• The Earth is made up of three layers: the crust, the mantle and the core.
• Crust the thin and solid outermost layer of Earth above the mantle
• Mantle the layer of rock between Earth’s crust and core
• Core the center part of the Earth below the mantle

• Earth’s interior gets warmer with depth.
• Geologists believe that the mantle is much hotter than the crust, reaching temperatures
higher than 1250° C (2280° F).
• The core is hotter than the mantle, reaching temperatures higher than 6000° C (10,800°
F).
• Radioactive elements contribute to Earth’s high internal temperature.
• The breakdown of radioactive isotopes uranium, thorium and potassium give off energy
that contributes to Earth’s high internal temperatures.

• Around 1915, German scientist Alfred Wegener proposed the idea that the continents were
once united as a supercontinent and then drifted apart.
• He pieced the continents together like a puzzle and called the supercontinent they
formed Pangaea.
• Wegener found identical fossils on widely separate continents, which supported his
idea.
• 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 mantle
• Plate tectonics the theory that explains how the outer parts of Earth change through time, and
that explains the relationships between continental drift, sea-floor spreading, seismic activity,
and volcanic activity
• It is unknown exactly why 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.

• Mid-ocean ridges result from divergent boundaries.
• The border between two plates is called a boundary.
• Divergent boundary a place where two plates are moving apart
• New rock forms between divergent boundaries.
• Magma liquid rock produced under Earth’s surface
• Oceanic plates dive beneath continental plates at convergent boundaries.
• Plates slide over each other at a convergent boundary.

• Subduction the process by which one lithospheric plate moves beneath another as a result of
tectonic forces
• The area where one plate slides over another is called a subduction zone. Subduction zones
produce ocean trenches, mountains, and volcanoes.
• 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.
• Colliding tectonic plates create mountains.
• When two plates collide, mountains are formed at the boundary of the collision.
• The Himalayas formed during the collision between the continental tectonic plate
containing India and the Eurasian continental plate.
• Transform fault boundaries can crack Earth.
• Plate movement can cause breaks in the lithosphere.
• Fault a crack in Earth created when rocks on either side of a break move
• Plate movement at transform fault boundaries is one cause of earthquakes.