Transcript Chapter 1: Meet Planet Earth

Chapter 1: Meet Planet Earth
Introduction
 No other planet in the solar system currently has
the right chemical and physical mix needed to
support life.
 No conclusive evidence of life existing elsewhere
in the universe has yet been discovered as far as
we know.
 Earth is unique.
Human Influences
 We human are influencing Earth’s external
geologic processes.
 More than 6 billion people.
Human Influences (2)
 Our daily activities are having measurable
effects on:
 Rainfall.
 Climate.
 Air.
 Water
quality.
 Erosion.
 In North America, we use 20 tons of mineral
resources per person/year.
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.
 They use ground-penetrating radar.
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.
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
 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
 Recently, a thin and very unusual rock layer, rich in the rare
metal iridium, 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.
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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.
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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.”)
Geologic Time and Earth’s Age
 The Appalachians rose about 300 million years ago.
 The modern Rockies about 70 million years.
 The most recent great ice sheets retreated about 12,000
years ago.
The Solar System
 Earth is part of the solar system.
 Solar system consists of:
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The sun.
Nine planets.
Over five dozen moons.
Vast numbers of asteroids.
Millions of comets.
Innumerable small fragments of rock and dust called meteoroids.
Figure 1.9 A
Figure 1.9 B
The Planets
 The solar system’s nine planets can be divided into two
groups:
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The terrestrial planets: Mercury, Venus, Earth, Mars.
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Closest to the sun.
– Small, rocky, and dense (3g/cm3 or greater).
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The Jovian planets: Jupiter, Saturn, Uranus, Neptune, Pluto.
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Farther from the sun than Mars.
Much larger than the terrestrial planets.
Much less dense.
Pluto is a structural exception in the Jovian planets.
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Is it a planet or an asteroid?
Figure 1.7 a
Figure 1.7 b
More on the Jovian Planets
 All of these planets are likely to have solid cores.
 They consist largely of the very light elements and
volatile substances:
 hydrogen.
 helium.
 carbon dioxide.
 ammonia.
Origin of the Solar System and Earth
 Birth began in a huge volume of space where earlier stars
had exploded into supernovas, producing a swirling cloud of
cosmic gas.
 Over millions of years, gravity slowly gathered the thinly
spread atoms into a thicker gas.
 Near the center of this gathering cloud the temperature and
density became so great that hydrogen atoms began to fuse
to form helium atoms (a nuclear reactor).
 The outer portion of the cosmic gas cloud cooled and
became dense enough to allow solid objects to condense
(planets, moons, and the other solid objects of the solar
system).
Planet Temperature
 Planets and moons nearest the sun (highest temperature)
contain:
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Compounds that condense only at high temperature (iron, silicon,
magnesium, and aluminum), most bind strongly with oxygen.
 Planets and moons more distant from the sun (lower
temperature) contain:
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Volatile substances (hydrogen and sulfur combined with oxygen).
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Moons of Jupiter:
 Io is red because it is rich in sulfur.
 Europa, smallest of Jupiter’s four large moons, contains a substantial
amount of ice.
Figure 1.10
Planetary Accretion and Meteorites
 Meteorites and the scars of ancient impacts provide
evidence of the way terrestrial planets grew to their
present sizes.
 This growth process is called planetary accretion.
 Planetary accretion continues to happen today.
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
 The mantle between the bottom of the asthenosphere 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:
 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:
 The outer 100 km of the solid Earth, where rocks are
harder and more rigid than those in the plastic
asthenosphere.
Plate Tectonics (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 System Concept
 A system in any portion of the universe that can be
isolated from the rest of the universe for observing
and measuring change.
 The simplest kind to understand is an isolated
system.
 the boundary completely prevents the exchange of either
matter or energy.
The System Concept (2)
 The nearest thing to an isolated system in the real
world is a closed system:
 exchanges energy with its surroundings, but not matter.
 An open system can exchange both energy and
matter across its boundary.
Figure 1.14
Figure 1.15
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.
Other Cycles
 The other cycles include the biogeochemical cycles:
 Carbon.
 Oxygen.
 Nitrogen.
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
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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
Figure B1.2
Figure B1.3
Changes Caused By Human Activities
 Human are affecting the Earth system in many ways:
 Burning petroleum and coal, which increases the
greenhouse effect.
 Intensive farming activities, which have an impact on
soil, ground and surface water.
 Production and release of gases containing chlorine,
which destroys ozone.
 Redistribution of water through the construction of giant
reservoirs, which changes the distribution of weight at
Earth’s surface and alters, slightly but measurably, the
rotation of the Earth on its axis.