Download Chapter 1: Meet Planet Earth

Meet Planet Earth
Geology
 Geology is the science of Earth.
 Geologists study the Earth’s processes, such as:
 Volcanism.
 Glaciation.
 Stream-flow.
 Rock formation.
Geologists Also Study :
 Chemistry, to understand:
– Minerals.
– Dissolved minerals.
– Minerals resources.
– Rocks formation.
– Ground water.
Geologists Also Study :(2)
 Physics, to understand:
– Plate tectonics.
– Volcanism.
– Earthquakes.
– Landslides.
 Biology, to understand:
– How life processes integrate with other Earth
systems.
– How life has evolved.
– Fossils in the rocks.
Geologists Also Study : (3)
 Meteorology, to understand:
– Stream flow.
– Groundwater levels.
 Oceanography, to understand:
– Seafloor’s role in plate tectonics.
– Shorelines.
Geologists Also Study : (4)
 Astronomy.
 Mathematics.
 Computer sciences.
 Economics, to understand how humans employ:
– Minerals.
– Energy resources.
What Do Geologists Do ?
 They seek to understand all processes that operate
on and inside the Earth.
 They study:
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Our planet’s long history.
Water bodies (rivers and lakes).
Hazardous processes such as earthquakes, volcanic eruptions, flood,
and landslides.
Rocks.
Spot surface patterns.
Physical Versus Historical Geology
 Historical geology
 Chronology of events, both physical and biological, that
have occurred in the past.
 The past is the biggest clue to the present.
 Physical geology
 Concerned with understanding the processes and the
materials.
Physical Geology Also Studies
 Plate
tectonics.
 Volcanism.
 Earthquakes.
 Landslides.
 Floods.
 Formation of
mineral deposits.
 Mountain-building.
 Shore erosion.
 Landscape formation.
 Rocks.
 Minerals.
 Air.
 Seawater.
 Soil.
 Sand
The Scientific Method (1)
 Geologists use a research strategy called the
scientific method.
 The scientific method includes the following steps:
 Observe and measure.
 Form a hypothesis (a plausible, but unproved,
explanation for the way something happens).
The Scientific Method (2)
 Test the hypothesis (by comparing the predictions against
the new observations).
 Formulate a theory (a generalization about natural
phenomena).
 Formulate a law or principle (statements that some
natural phenomenon is invariably observed to happen in
the same way, and no deviations have ever been
observed).
 Continually reexamine the law or principle in the light of
new evidence.
How Rapid Are Geologic Processes?
 During the seventeenth and eighteenth centuries,
people believed that Earth’s features (mountains,
valleys, oceans, rivers) were permanent and had
been produced by a few great upheavals.
 This theory is called Catastrophism災變說.
James Hutton Applies the Scientific
Method
 James Hutton (1726-1797), now known as the
father of modern scientific geology, assembled
evidence and proposed a counterhypothesis called
gradualism.
 In 1795, he published “Theory of the Earth with
Proofs and Illustrations.”
 He proposed uniformitarianism, which asserts that
everything must move slowly in a repetitive,
continuous cycle.
Uniformitarianism 【地】均變說
 States that the same processes we observe today
have been operating throughout Earth’s history.
 The cycle of uplift, erosion, transport, deposition,
solidification into rock, and renewed uplift requires
a great deal of time for its operation.
 The Earth is 4.55 billion years old.
Catastrophism災變說
 Recently, a thin and very unusual rock layer, rich in the rare
metal iridium 【化】銥, has been discovered at many
locations worldwide.
 It indicates that a catastrophic impact from a meteor may
have occurred about 66 million years ago.
 The mass extinction of dinosaurs occurred at that time.
 More dramatic extinctions have occurred at other times in the past.

The mass extinction occurring about 245 million years ago
eliminated almost 90 percent of all plants and animals living at
the time.
 Events such as earthquakes, volcanic eruptions, tsunami,
floods, and landslides are local catastrophes.
Geologic Time and Earth’s Age
 Stratigraphy is the study of the structure of sedimentary
layers recording a sequence of past events.
–
The layers at the bottom of the pile are the oldest.
– Those at the top are the youngest.
 Stratigraphy identifies the relative age of many geologic
events.
 Relative age identifies position in a limited sequence. (“This is older
than that.”)
 Radioactivity can be used to establish the absolute age of
geologic events.
 Absolute age identifies position in a universal sequence (such as our
current system of naming years in chronological order). (“This is
49,000 years old.”)
Earth’s Internal Structure
 When a meteorite impacts a planet or moon, its energy of
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motion (called kinetic energy) is transformed into heat
energy.
As Earth grew larger and larger from continual impacts, its
temperature increased.
Radioactive decay of materials like uranium, thorium and
potassium also added heat.
Because Earth became partly fluid, less-dense molten
materials (silicon, aluminum, sodium, and potassium) were
freed to migrate toward the surface.
Denser melted materials, such as molten iron, sank toward
the center of the planet.
The Earth’s Interior
 Planet Earth has three main parts:
 At
the center is the densest part, the core (metallic iron,
nickel).
 Surrounding the core is the mantle.
 Surrounding the mantle lies the thinnest and outermost
layer, the crust.
Figure 1.13
The Earth’s Crust
 The crust is not uniform.
 The oceanic crust on average is about 8 km thick.
 The continental crust on average is about 45 km thick.
Investigating the Earth’s Interior
 How do we know anything about the composition
of the core and the mantle?
 By measuring the time required for earthquake waves to
travel through Earth by different paths, we can determine
the composition of the materials through which they
move.
 Iron meteorites are believed to be fragments from the
core of a small terrestrial planet that was shattered by a
gigantic impact.
The Layers of the Earth’s Interior (1)
 The inner core
 Pressures are so great that iron is solid, despite its high temperature.
 The outer core
 Iron is molten and exists as a liquid.
 The Mesosphere中層圈
 The mantle地函 between the bottom of the asthenosphere軟流圈 to
the core-mantle boundary.
 The temperature at the core-mantle boundary is about 50000C.
The Layer of the Earth’s Interior (2)
 The Asthenosphere:軟流圈
 The region of the mantle where rocks become ductile,
have little strength, and are easily deformed. It lies at a
depth of 100 to 350 km below the surface.
 The Lithosphere: 岩石圈
 The outer 100 km of the solid Earth, where rocks are
harder and more rigid than those in the plastic
asthenosphere.
Figure 1.13
Plate Tectonics 板塊構造(1)
 The Earth gets rid of heat and keeps a nearly
constant internal temperature through convection in
the mesosphere and asthenosphere.
 Plate tectonics theory says that Earth’s outermost
100 km “eggshell” (the lithosphere) is cracked in
about a dozen large pieces.
Plate Tectonics (2)
 In the 1960s, research by many geologists and
oceanographers melded into the revolutionary hypothesis of
plate tectonics.
 Plate tectonics is a group of processes by which large
fragments (plates) of lithosphere move horizontally across
the surface of the Earth. Through their movements and
interactions, they generate:
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Earthquakes.
Volcanism.
Mountain-building.
Other geologic processes.
The Earth System (1)
 The Earth system is composed of:
 The geosphere (rocks).
 The atmosphere (air).
 The hydrosphere (water).
 The biosphere (life in all its forms).
 Energy and materials (like water, carbon, and minerals) are
transferred from one system to another.
 To a close approximation, Earth is a closed system.
The Earth System (2)
 Earth is only approximately a closed system
because:
 Meteorites do come in from space and fall on Earth.
 A tiny trickle of gases leaves the atmosphere and escapes
into space.
 Earth is comprised of four open systems.
Our Planet’s “Four Spheres”
 The atmosphere:
 Nitrogen, oxygen, argon, carbon dioxide, and water vapor.
 The hydrosphere:
 Oceans, lakes, streams, underground water, snow, and ice.
 The biosphere:
 All of Earth’s organisms, as well as any organic matter not yet
decomposed.
 The geosphere:
 The solid Earth from core to surface, composed principally of rock
and regolith.
Figure 1.16
Cyclical Movements
 The movement of materials is continuous.
 There are two key aspects to cycles:
 The reservoirs in which the materials reside.
 The flows, or fluxes, of materials from reservoir to
reservoir.
 The speed of movement differs greatly in different
cycles.
Figure 1.17
The Three Most Important Cycles
 The hydrologic cycle:
 Water in Earth’s hydrosphere.
 The rock cycle:
 Rock is formed, modified, decomposed,and reformed by
the internal and external processes of Earth.
 The tectonic cycle:
 Movements of plates of lithosphere, and the internal
processes of Earth’s deep interior that drive plate motions.
The Hydrologic Cycle
 The hydrologic cycle:
 Is powered by heat from the sun.
 Encompasses the movement of water in the atmosphere,
in the hydrosphere, on the Earth’s surface, and in the
Earth’s crust.
Figure 1.18
The Rock Cycle
 Rock is any naturally formed, nonliving, firm and coherent
aggregate of mineral matter that constitutes part of a planet.
 The three rock families:
 Igneous rock:
Created through the cooling and solidification of magma
 Sedimentary rock:
 Formed from deposits of sediment
 Metamorphic rock:
 Formed by the effects of pressure and heat on existing rocks

The Rock Cycle (2)
 The rock cycle describes all the processes by which
rock is:
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Formed.
Transported.
Decomposed.
Reformed.
 Active volcanoes produce igneous rocks.
 Mountain ranges rise as a result of plate tectonics.
 Weathering and erosion change the surface of the
solid Earth.
The Rock Cycle (3)
 The sediment is buried and compacted, eventually
becoming sedimentary rock.
 Deeper burial turns sedimentary rock into
metamorphic rock.
 Even deeper burial may cause some of the
metamorphic rock to melt, forming magma from
which new igneous rock will form.
Figure 1.19
The Tectonic Cycle
 Tectonics is the study of the movement and
deformation of the lithosphere.
 When magma rises from deep in the mantle, it
forms new oceanic crust at midocean ridges.
 The lifetime of oceanic crust is shorter than the
lifetime of continental crust.
 The most ancient oceanic crust of the ocean basins is only
about 180 million years old, and the average age of all
oceanic crust is about 70 million years old.
The Tectonic Cycle (2)
 When all oceanic crust sinks back into the mantle, it
carries some water with it.
 The water is driven off during volcanic eruptions.
 Some constituents in the hot rock (calcium,
magnesium) are the same as those of seawater.
Figure 1.20
Figure 1.21