Download Integrated Science Chapter 19 Notes Section 1: Earth`s Interior and

Integrated Science
Chapter 19 Notes
Section 1: Earth’s Interior and Plate Tectonics
1. The Earth’s Interior
• The Earth is composed of many layers
⇒ The crust – the outermost and thinnest layer of Earth
→ The crust is relatively cool and made up of hard, solid rock
→ Oceanic crust – the crust beneath the oceans
→ Continental crust – less dense than oceanic crust
⇒ The mantle – the layer of rock between the Earth’s crust and its core
→ Denser than the crust
→ Almost 2,900 km (1,800miles) thick
→ In the outer mantle the rocks are mostly solid
→ The inner mantle is extremely hot and rock is soft and easily deformed
⇒ The core – the center of a planetary body
→ Composed mainly of iron and nickel
→ The inner core is solid metal
→ The outer core, which surround the inner core is liquid metal
• The Earth’s interior gets warmer with depth
• Radioactive elements contribute to Earth’s high internal temperature
2. Plate Tectonics
• In the early 20th century, German scientist Alfred Wegener proposed that 200 million years ago all
the current continents were joined together in one supercontinent he called Pangaea
⇒ Evidence included continents’ coastlines that fit like puzzle pieces and fossil records
indicating that the same kind of animals lived on all the continents
• Earth has plates that move over the tar-like mantle
⇒ Lithosphere – the thin outer shell of Earth, consisting of the crust and the rigid upper mantle
⇒ The lithosphere is approximately 100 km thick
⇒ Made up of seven large pieces (and several small pieces) called tectonic plates
⇒ Plate tectonics – the theory that Earth’s surface is made up of large moving plates
⇒ Some plates move toward each, some away from each other, and some move alongside
each other
⇒ The plates can move from 1 cm to 16 cm per year
• It is not known exactly why tectonic plates move
⇒ One hypothesis suggests that plate movement results from convection currents in
asthenosphere
⇒ Asthenosphere – the zone of the mantle beneath the lithosphere that consists of slowly
flowing solid rock
⇒ Some scientists do not support the hypothesis of convection currents, so it is not clear what
force causes the plates to move
• A divergent boundary occurs where two plates move apart creating a gap between them
⇒ Magma rises from the asthenosphere and cools, forming new lithospheric rock
⇒ Magma – molten rock within the Earth
⇒ Mid-oceanic ridges are mountain ranges the form at divergent boundaries
⇒ Surrounded on two sides by the mountain ranges, a rift valley is formed by the magma
• A convergent boundary occur where oceanic plates dive beneath continental or oceanic plates
⇒ Subduction – the process in which a tectonic plate dives beneath another tectonic plate and
into the asthenosphere
⇒ Ocean trenches, mountain, and volcanoes are formed at subduction zones
•
⇒ Oceanic crust melts when it subducts
→ In subduction zones, when the oceanic plate dives into the hotter mantle, the materials in
the plate reach their boiling point and start to melt, forming magma.
→ Because the magma is less dense than the rock above it, it rises toward the surface; this
rising magma pushes the continental crust upward forming mountains
→ Volcanic mountains also form at convergent boundaries
⇒ Colliding continental plates create mountains
→ Example: the Himalayas were formed by a collision between the India and Eurasian
plates
Fault – a crack in the Earth created when rocks on either side of a break move
⇒ Transform fault boundaries occur when tectonic plates move horizontally past each other
⇒ This movement requires great force and are called earthquakes
Section 2: Earthquakes and Volcanoes
1. Earthquakes
• Earthquakes generally occur at the boundaries of tectonic plates, where the plates shift with
respect to one another
⇒ As the plates move the rocks along their edges experience immense pressure
⇒ When the pressure is great enough the rocks break along the fault line, and the energy is
released in seismic waves
⇒ Focus – the area along a fault at which slippage first occurs, initiating an earthquake
⇒ Earthquake waves travel in all directions from the focus
⇒ Epicenter – the point in Earth’s surface directly above the focus of the earthquake
• Energy from earthquakes is transferred through Earth by waves
⇒ The energy released by an earthquake is measured as shock waves
⇒ Earthquakes generate three type of waves:
→ Longitudinal waves originate from the earthquake’s focus and move very rapidly through
the rock
♦ P waves – primary waves; the longitudinal waves generated by an earthquake
→ Transverse waves is the second type of wave originating from an earthquake’s focus
♦ The transverse waves move more slowly than the longitudinal waves
♦ S waves – secondary waves; the transverse waves generated by an earthquake
→ Surface waves – a seismic wave that travels along Earth’s surface
♦ The third type of earthquake wave, surface waves are low frequency and cause the
Earth to shake like a bell that has been rung
♦ Surface waves are more destructive than either the P waves or the S waves
• Seismology is the science of detecting and measuring earthquakes
⇒ Seismology – the study of earthquake sand related phenomena
⇒ Scientist use machines called seismographs to record data from earthquakes, include P
waves, S waves, and surface waves
→ The records of seismic activity are called seismograms
→ Three seismograph stations are required to locate the epicenter of an earthquake
⇒ Seismographs are also used to investigate Earth’s interior
⇒ The Richter scale is used to measure the magnitude of earthquakes
→ Richter scale – scale that expresses the relative magnitude of an earthquake
→ Each step on the Richter scale represents a 30-fold increase in the energy released by
the earthquake
→ An earthquake with a magnitude of 8 releases 810,000 times as much energy as an
earthquake with a magnitude of 4
2. Volcanoes
• Volcanoes can result from the movement of tectonic plates
⇒ A volcano is opening in the Earth’s crust through which magma has reached Earth’s surface
⇒ Vent – an opening through which molten rock flows onto Earth’s surface
• The type of eruption determines the volcano type
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•
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⇒ When magma reaches the surface, its physical behavior changes, and it is called lava
⇒ There are three types of volcanoes
→ A shield volcano produces magma rich in iron and magnesium which is very fluid so the
lava flows great distances.
♦ Eruptions from shield volcanoes are usually mild and can occur several times.
♦ The buildup of this lava produces a gently sloping mountain
→ Composite volcanoes are made up of alternating layers of ash, cinders, and lava
♦ The magma from composite volcanoes is rich in silica, and is thicker than the lave
from shield volcanoes
♦ Gases are trapped in the magma causing eruptions that alternate between flows and
explosive activity that produces cinders and ash.
♦ Composite volcanoes are typically thousands of meters high and have steep slopes
→ Cinder cones are the smallest and most abundant volcano type
♦ Large amounts of gas are trapped in magma, resulting in violent eruptions with vast
quantities of hot ash and lava thrown from the vent
♦ Cinder cones tend to be active for only a short period and then become dormant
⇒ Volcanoes can form under the oceans, these underground volcanoes are called seamounts
Volcanoes can occur at convergent plate boundaries
Volcanoes can occur at divergent plate boundaries
Volcanoes can occur at hot spots
⇒ These volcanoes occur in the middle of plates
⇒ Mushroom shaped trails of hot magma called mantle plumes, rise from deep inside the
mantle and erupt at hot spots at the surface
⇒ If the resulting volcanoes grow big enough they will break the surface of the ocean and form
islands
⇒ While the plates move the mantle plumes stay in the same place, so over time they can form
a chain of islands
→ Example: the Hawaiian Islands
Section 3:Minerals and Rocks
1. Structure and origin of rocks
• All rocks are composed of minerals
⇒ Mineral – a natural, inorganic solid with a definite chemical composition and a characteristic
internal structure
• Molten rock cools to form igneous rock
⇒ Igneous rock – rock formed from cooled and hardened magma or lava
→ Extrusive igneous rocks cool on the Earth’s surface
→ Intrusive igneous rocks cool while trapped below the surface
• Remains of older rocks and organisms form sedimentary rocks
⇒ Weathering – change in the physical form or chemical composition of rock materials
exposed at Earth’s surface
→ Sedimentary rock – rock formed from compressed or cemented deposits of sediment
→ Fossils – the traces or remains of a plant or an animal found in sedimentary rock
→ Sedimentary rocks are named according to the size of the fragments they contain
⇒ Rocks that undergo pressure and heating without melting form metamorphic rock
→ Metamorphic rock – rock formed from other rocks as a result of heat, pressure, or
chemical processes
• Old rocks in the rock cycle form new rocks
2. How old are rocks
• Rocks form and change over millions of years, so it is difficult to know the exact time a rock was
formed
• The relative age of rocks can be determined using the principle of superposition
⇒ The principle of superposition states:
Assuming no change in the position of the rock layers,
the oldest rock will be on the bottom, and the youngest rock will be on the top
•
⇒ The principle is useful in studying the sequence of life on Earth
Radioactive dating can determine a more exact, or absolute, age of rocks
⇒ Radioactive isotopes decay at a regular rate
⇒ Geologist can use the rate of decay to determine the age of the rock containing the isotope
Section 4: Weathering and Erosion
1. Physical weathering
• Occurs when rocks are broken into smaller pieces without changing the chemical composition of
the rock
⇒ Ice and plants can break rocks
2. Chemical weathering
• Occurs when a reaction between compounds or elements results in a change in the composition
of the rock
⇒ Carbon dioxide dissolved in water can cause chemical weathering
⇒ Acid rain slowly dissolves minerals
→ Acid rain – precipitation that has an unusually high concentration of sulfuric or nitric
acids resulting from chemical pollution in the air
3. Erosion
• Erosion is the removal and transportation of weathered and nonweathered materials by running
water, wind, waves, ice, underground water, and gravity
⇒ Water erosion shapes Earth’s surface
→ Erosion – the process by which rock and/or products of weathering are removed
→ Deposition – process in which sediment is laid down
⇒ Glaciers erode mountains
⇒ Wind can also shape the landscape