Discovering the Universe 8ed Neil F. Comins William J. Kaufmann III Earth and Moon

WHAT DO YOU THINK? 1. How old is the Earth? How do we know?? 2. Can Earth’s ozone layer, which is now being depleted, be replenished? 3. What is the greenhouse effect? Is Global Warming real? 4. What causes the ocean tides? 5. Do we see all parts of the Moon’s surface at some time throughout the lunar cycle? 6. How did the moon form? How do we know?

When did the planets form? We cannot find the age of a planet, but we can find the ages of the rocks that make it up. We cannot find the age of a planet, but we can find the ages of the rocks that make it up. We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it. We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it.

Radioactive Decay Some isotopes decay into other nuclei. Some isotopes decay into other nuclei. A half-life is the time for half the nuclei in a substance to decay. A half-life is the time for half the nuclei in a substance to decay.

Thought Question Suppose you find a rock originally made of potassium-40, half of which decays into argon-40 every 1.25 billion years. You open the rock and find 15 atoms of argon-40 for every atom of potassium-40. How long ago did the rock form? A billion years ago B. 2.5 billion years ago C billion years ago D. 5 billion years ago

Thought Question Suppose you find a rock originally made of potassium-40, half of which decays into argon-40 every 1.25 billion years. You open the rock and find 15 atoms of argon-40 for every atom of potassium-40. How long ago did the rock form? A billion years ago B. 2.5 billion years ago C billion years ago D. 5 billion years ago

Age dating of meteorites that are unchanged since they condensed and accreted tells us that the solar system is about 4.6 billion years old. Dating the Solar System

Radiometric dating tells us that the oldest moon rocks are 4.4 billion years old. Radiometric dating tells us that the oldest moon rocks are 4.4 billion years old. The oldest meteorites are 4.55 billion years old. The oldest meteorites are 4.55 billion years old. Planets probably formed 4.5 billion years ago. Planets probably formed 4.5 billion years ago. But Earth’s crust rocks date to 3 or 4 billion years only… why? But Earth’s crust rocks date to 3 or 4 billion years only… why?

“Professor, didn’t YOU say every measurement in science is uncertain??? Couldn’t YOU be wrong?” “Professor, didn’t YOU say every measurement in science is uncertain??? Couldn’t YOU be wrong?” “The Earth is the center of the universe.” “The Earth is the center of the universe.” “The Earth is flat.” “The Earth is flat.” “The continents are fixed upon Earth.” “The continents are fixed upon Earth.” “Chernobyl and Three-Mile-Island are safe” “Chernobyl and Three-Mile-Island are safe” “Intelligence is determined by race.” “Intelligence is determined by race.” Dating the Earth…

Good science… Good science… Seeks natural laws to explain similar phenomena Seeks natural laws to explain similar phenomena Adapts to new data Adapts to new data Looks for patterns and corroboration Looks for patterns and corroboration Requires independent lines of evidence Requires independent lines of evidence Depends upon experiment, not personal values Depends upon experiment, not personal values Dating the Earth…

The Origin of the Moon: An Example of the Process of Science Where did the moon come from? Where did the moon come from? How do we know? How do we know?

How do we explain the existence of our Moon? Terrestrial planets don’t have moons…. Our Moon is VERY large compared to its “partner” Composition is both like Earth… Rocky materials, similar to Earth’s Crust …and NOT like Earth: No water, no atmosphere, not a large metal core

How do we explain the existence of our Moon? FOUR (4) Theories Formed at the same time, alongside Earth Formed from Earth’s materials Captured as it passed by Result of Giant Impact

How do we explain the existence of our Moon? Formed at the same time, alongside Earth The “Sister” Theory… But then Should have the same composition… Should have water & “volatiles” Should have similar density It doesn’t, so rule this one out…

How do we explain the existence of our Moon? Formed from Earth’s materials As earth formed, it “spun out” “Fission Theory” But then…. again Should have water & “volatiles” Should have similar density It doesn’t, so rule this one out…

How do we explain the existence of our Moon? Captured as it passed by “Capture Theory” But then…. How can this be done? It is very unlikely, so rule this one out…

Captured Moons The unusual moons of some planets may be captured planetesimals. The unusual moons of some planets may be captured planetesimals.

How do we explain the existence of our Moon? Result of Giant Impact Mars-sized impactor strikes Earth a glancing blow Impactor destroyed, creates a debris ring Gravity takes over….the Moon is born. Lacks “volatiles” and water & Iron Computer models show this to be possible!

Giant Impact Giant impact stripped matter from Earth’s crust Stripped matter began to orbit Then accreted into Moon

Earth as a Planet Our goals for learning: Why is Earth geologically active? Why is Earth geologically active? What processes shape Earth’s surface? What processes shape Earth’s surface? How does Earth’s atmosphere affect the planet? How does Earth’s atmosphere affect the planet?

Why is Earth geologically active?

Earth’s Interior Core: Highest density; nickel and iron Core: Highest density; nickel and iron Mantle: Moderate density; silicon, oxygen, etc. Mantle: Moderate density; silicon, oxygen, etc. Crust: Lowest density; granite, basalt, etc. Crust: Lowest density; granite, basalt, etc.

Terrestrial Planet Interiors Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like. Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like.

Why do water and oil separate? A. Water molecules repel oil molecules electrically. B. Water is denser than oil, so oil floats on water. C. Oil is more slippery than water, so it slides to the surface of the water. D. Oil molecules are bigger than the spaces between water molecules.

Why do water and oil separate? A. Water molecules repel oil molecules electrically. B. Water is denser than oil, so oil floats on water. C. Oil is more slippery than water, so it slides to the surface of the water. D. Oil molecules are bigger than the spaces between water molecules.

Differentiation Gravity pulls high-density material to center Gravity pulls high-density material to center Lower-density material rises to surface Lower-density material rises to surface Material ends up separated by density Material ends up separated by density

Thought Question What is necessary for differentiation to occur in a planet? A. It must have metal and rock in it. B. It must be a mix of materials of different density. C. Material inside must be able to flow. D. All of the above. E. b and c.

Thought Question What is necessary for differentiation to occur in a planet? A. It must have metal and rock in it. B. It must be a mix of materials of different density. C. Material inside must be able to flow. D. All of the above. E. b and c.

Lithosphere A planet’s outer layer of cool, rigid rock is called the lithosphere. A planet’s outer layer of cool, rigid rock is called the lithosphere. It “floats” on the warmer, softer rock that lies beneath. It “floats” on the warmer, softer rock that lies beneath.

Thought Question Do rocks s-t-r-e-t-c-h? A. No—rock is rigid and cannot deform without breaking. B. Yes—but only if it is molten rock. C. Yes—rock under strain may slowly deform.

Thought Question Do rocks s-t-r-e-t-c-h? A. No—rock is rigid and cannot deform without breaking. B. Yes—but only if it is molten rock. C. Yes—rock under strain may slowly deform.

Strength of Rock Rock stretches when pulled slowly but breaks when pulled rapidly. Rock stretches when pulled slowly but breaks when pulled rapidly. The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere. The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.

Heat Drives Geological Activity Convection: hot rock rises, cool rock falls. One convection cycle takes 100 million years on Earth.

Sources of Internal Heat 1. Gravitational potential energy of accreting planetesimals 2. Differentiation 3. Radioactivity

Heating of Interior over Time Accretion and differentiation when planets were young Accretion and differentiation when planets were young Radioactive decay is most important heat source today Radioactive decay is most important heat source today

Cooling of Interior Convection transports heat as hot material rises and cool material falls Convection transports heat as hot material rises and cool material falls Conduction transfers heat from hot material to cool material Conduction transfers heat from hot material to cool material Radiation sends energy into space Radiation sends energy into space

Thought Question What cools off faster? A. A grande-size cup of Starbucks coffee B. A teaspoon of cappuccino in the same cup

Thought Question What cools off faster? A. A grande-size cup of Starbucks coffee B. A teaspoon of cappuccino in the same cup

Thought Question What cools off faster? A. A big terrestrial planet B. A tiny terrestrial planet

Thought Question What cools off faster? A. A big terrestrial planet B. A tiny terrestrial planet

Role of Size Smaller worlds cool off faster and harden earlier. Smaller worlds cool off faster and harden earlier. Moon and Mercury are now geologically “dead.” Moon and Mercury are now geologically “dead.”

Surface Area to Volume Ratio Heat content depends on volume. Heat content depends on volume. Loss of heat through radiation depends on surface area. Loss of heat through radiation depends on surface area. Time to cool depends on surface area divided by volume: Time to cool depends on surface area divided by volume: Larger objects have a smaller ratio and cool more slowly. Larger objects have a smaller ratio and cool more slowly.

Planetary Magnetic Fields Moving charged particles create magnetic fields. A planet’s interior can create magnetic fields if its core is electrically conducting, convecting, and rotating.

Earth’s Magnetosphere Earth’s magnetic fields protects us from charged particles from the Sun. The charged particles can create aurorae (“Northern lights”).

Thought Question If the planet core is cold, do you expect it to have magnetic fields? A. Yes, refrigerator magnets are cold, and they have magnetic fields. B. No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

Thought Question If the planet core is cold, do you expect it to have magnetic fields? A. Yes, refrigerator magnets are cold, and they have magnetic fields. B. No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

Special Topic: How do we know what’s inside a planet? P waves push matter back and forth. P waves push matter back and forth. S waves shake matter side to side. S waves shake matter side to side.

Special Topic: How do we know what’s inside a planet? P waves go through Earth’s core, but S waves do not. P waves go through Earth’s core, but S waves do not. We conclude that Earth’s core must have a liquid outer layer. We conclude that Earth’s core must have a liquid outer layer.

What processes shape Earth’s surface?

Geological Processes Impact cratering Impact cratering — Impacts by asteroids or comets Volcanism Volcanism — Eruption of molten rock onto surface Tectonics Tectonics — Disruption of a planet’s surface by internal stresses Erosion Erosion — Surface changes made by wind, water, or ice

Impact Cratering Most cratering happened soon after the solar system formed. Most cratering happened soon after the solar system formed. Craters are about 10 times wider than objects that made them. Craters are about 10 times wider than objects that made them. Small craters greatly outnumber large ones. Small craters greatly outnumber large ones. The Production of a Crater

Impact Craters Meteor Crater (Arizona) Tycho (Moon)

Volcanism Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface. Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface. Molten rock is called lava after it reaches the surface. Molten rock is called lava after it reaches the surface. Volcanic Eruptions and Lava Flows

Lava and Volcanoes Runny lava makes flat lava plains. Slightly thicker lava makes broad shield volcanoes. Thickest lava makes steep stratovolcanoes.

Outgassing Volcanism also releases gases from Earth’s interior into the atmosphere. Volcanism also releases gases from Earth’s interior into the atmosphere.

Tectonics Convection of the mantle creates stresses in the crust called tectonic forces. Convection of the mantle creates stresses in the crust called tectonic forces. Compression forces make mountain ranges. Compression forces make mountain ranges. A valley can form where the crust is pulled apart. A valley can form where the crust is pulled apart. Tectonics and Convection of the Mantle

Plate Tectonics on Earth Earth’s continents slide around on separate plates of crust. Earth’s continents slide around on separate plates of crust. Plate Tectonics on Earth

Erosion Erosion is a blanket term for weather- driven processes that break down or transport rock. Erosion is a blanket term for weather- driven processes that break down or transport rock. Processes that cause erosion include Processes that cause erosion include — Glaciers — Rivers — Wind

Erosion by Water The Colorado River continues to carve the Grand Canyon. The Colorado River continues to carve the Grand Canyon.

Erosion by Ice Glaciers carved the Yosemite Valley. Glaciers carved the Yosemite Valley.

Erosion by Wind Wind wears away rock and builds up sand dunes. Wind wears away rock and builds up sand dunes.

Erosional Debris Erosion can create new features by depositing debris. Erosion can create new features by depositing debris.

How does Earth’s atmosphere affect the planet ? Which Molecules are Greenhouse Gases?

Effects of Atmosphere on Earth 1. Erosion 2. Radiation protection 3. Greenhouse effect 4. Makes the sky blue!

Radiation Protection All X-ray light is absorbed very high in the atmosphere. All X-ray light is absorbed very high in the atmosphere. Ultraviolet light is absorbed by ozone (O 3 ). Ultraviolet light is absorbed by ozone (O 3 ).

The Greenhouse Effect Which Molecules are Greenhouse Gases?

Earth’s atmosphere absorbs light at most wavelengths.

Greenhouse effect: Certain molecules let sunlight through but trap escaping infrared photons. (H 2 O, CO 2, CH 4 ) The Green House Effect

Thought Question Why is the sky blue? Why is the sky blue? A. The sky reflects light from the oceans. B. Oxygen atoms are blue. C. Nitrogen atoms are blue. D. Air molecules scatter blue light more than red light. E. Air molecules absorb red light.

Thought Question Why is the sky blue? Why is the sky blue? A. The sky reflects light from the oceans. B. Oxygen atoms are blue. C. Nitrogen atoms are blue. D. Air molecules scatter blue light more than red light. E. Air molecules absorb red light.

A Greenhouse Gas Any gas that absorbs infrared Any gas that absorbs infrared Greenhouse gas: molecules with two different types of elements (CO 2, H 2 O, CH 4 ) Greenhouse gas: molecules with two different types of elements (CO 2, H 2 O, CH 4 ) Not a greenhouse gas: molecules with one or two atoms of the same element (O 2, N 2 ) Not a greenhouse gas: molecules with one or two atoms of the same element (O 2, N 2 )

Greenhouse Effect: Bad? The Earth is much warmer because of the greenhouse effect than it would be without an atmosphere…but so is Venus.

Why the sky is blue Atmosphere scatters blue light from the Sun, making it appear to come from different directions. Atmosphere scatters blue light from the Sun, making it appear to come from different directions. Sunsets are red because less of the red light from the Sun is scattered. Sunsets are red because less of the red light from the Sun is scattered.

Origin of Earth’s Water Water may have come to Earth by way of icy planetesimals and comets from the outer solar system. Water may have come to Earth by way of icy planetesimals and comets from the outer solar system.

Summary of Key Ideas

Earth: A Dynamic, Vital World Earth’s atmosphere is about four-fifths nitrogen and one-fifth oxygen. This abundance of oxygen is due to the biological processes of life-forms on the planet. Earth’s atmosphere is about four-fifths nitrogen and one-fifth oxygen. This abundance of oxygen is due to the biological processes of life-forms on the planet. Earth’s atmosphere is divided into layers named the troposphere, stratosphere, mesosphere, and ionosphere. Earth’s atmosphere is divided into layers named the troposphere, stratosphere, mesosphere, and ionosphere. Ozone molecules in the stratosphere absorb ultraviolet light rays. Ozone molecules in the stratosphere absorb ultraviolet light rays. The outermost layer, or crust, of Earth offers clues to the history of our planet. The outermost layer, or crust, of Earth offers clues to the history of our planet. Earth’s surface is divided into huge plates that move over the upper mantle. Movement of these plates, a process called plate tectonics, is caused by convection in the mantle. Also, upwelling of molten material along cracks in the ocean floor produces seafloor spreading. Plate tectonics is responsible for most of the major features of Earth’s surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans. Earth’s surface is divided into huge plates that move over the upper mantle. Movement of these plates, a process called plate tectonics, is caused by convection in the mantle. Also, upwelling of molten material along cracks in the ocean floor produces seafloor spreading. Plate tectonics is responsible for most of the major features of Earth’s surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans.

Study of seismic waves (vibrations produced by earthquakes) shows that Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin, low-density crust. Earth’s inner and outer cores are composed primarily of iron. The mantle is composed of iron-rich minerals. Study of seismic waves (vibrations produced by earthquakes) shows that Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin, low-density crust. Earth’s inner and outer cores are composed primarily of iron. The mantle is composed of iron-rich minerals. Earth’s magnetic field produces a magnetosphere that surrounds the planet and blocks the solar wind. Earth’s magnetic field produces a magnetosphere that surrounds the planet and blocks the solar wind. Some charged particles from the solar wind are trapped in two huge, doughnut-shaped rings called the Van Allen radiation belts. A deluge of particles from a coronal mass ejection by the Sun can initiate an auroral display. Some charged particles from the solar wind are trapped in two huge, doughnut-shaped rings called the Van Allen radiation belts. A deluge of particles from a coronal mass ejection by the Sun can initiate an auroral display. Earth: A Dynamic, Vital World

The Moon and Tides The Moon has light-colored, heavily cratered highlands and dark-colored, smooth-surfaced maria. The Moon has light-colored, heavily cratered highlands and dark-colored, smooth-surfaced maria. Many lunar rock samples are solidified lava formed largely of minerals also found in Earth rocks. Many lunar rock samples are solidified lava formed largely of minerals also found in Earth rocks. Anorthositic rock in the lunar highlands was formed between 4.0 and 4.3 billion years ago, whereas the mare basalts solidified between 3.1 and 3.8 billion years ago. The Moon’s surface has undergone very little geologic change over the past 3 billion years. Anorthositic rock in the lunar highlands was formed between 4.0 and 4.3 billion years ago, whereas the mare basalts solidified between 3.1 and 3.8 billion years ago. The Moon’s surface has undergone very little geologic change over the past 3 billion years. Impacts have been the only significant “weathering” agent on the Moon; the Moon’s regolith (pulverized rock layer) was formed by meteoritic action. Lunar rocks brought back to Earth contain no water and are depleted of volatile elements. Impacts have been the only significant “weathering” agent on the Moon; the Moon’s regolith (pulverized rock layer) was formed by meteoritic action. Lunar rocks brought back to Earth contain no water and are depleted of volatile elements.

The Moon and Tides Frozen water may have been discovered at the Moon’s poles. Frozen water may have been discovered at the Moon’s poles. The collision-ejection theory of the Moon’s origin, accepted by most astronomers, holds that the young Earth was struck by a huge asteroid, and debris from this collision coalesced to form the Moon. The collision-ejection theory of the Moon’s origin, accepted by most astronomers, holds that the young Earth was struck by a huge asteroid, and debris from this collision coalesced to form the Moon. The Moon was molten in its early stages, and the anorthositic crust solidified from low-density magma that floated to the lunar surface. The mare basins were created later by the impact of planetesimals and were then filled with lava from the lunar interior. The Moon was molten in its early stages, and the anorthositic crust solidified from low-density magma that floated to the lunar surface. The mare basins were created later by the impact of planetesimals and were then filled with lava from the lunar interior. Gravitational interactions between Earth and the Moon produce tides in the oceans of Earth and set the Moon in synchronous rotation. The Moon is moving away from Earth, and, consequently, Earth’s rotation rate is decreasing. Gravitational interactions between Earth and the Moon produce tides in the oceans of Earth and set the Moon in synchronous rotation. The Moon is moving away from Earth, and, consequently, Earth’s rotation rate is decreasing.

Key Terms anorthosite capture theory cocreation theory collision-ejection theory continental drift convection core coronal mass ejection crust dynamo theory ejecta blanket fission theory highlands impact breccias ionosphere (thermosphere) mantle mare (plural maria) mare basalt mascons mesosphere neap tide northern lights (aurora borealis) ozone layer planetary differentiation plate tectonics regolith rille seafloor spreading seismic waves seismograph solar wind southern lights (aurora australis) spring tide stratosphere synchronous rotation troposphere Van Allen radiation belts

WHAT DID YOU THINK? Can Earth’s ozone layer, which is now being depleted, be naturally replenished? Can Earth’s ozone layer, which is now being depleted, be naturally replenished? Yes. Ozone is created continuously from normal oxygen molecules by their interaction with the Sun’s ultraviolet radiation. Yes. Ozone is created continuously from normal oxygen molecules by their interaction with the Sun’s ultraviolet radiation.

WHAT DID YOU THINK? Who was the first person to walk on the Moon, and when did this event occur? Who was the first person to walk on the Moon, and when did this event occur? Neil Armstrong was the first person to set foot on the Moon. He and Buzz Aldrin flew on the Apollo 11 spacecraft piloted by Michael Collins. Armstrong and Aldrin set down the Eagle Lander on the Moon on July 20, Neil Armstrong was the first person to set foot on the Moon. He and Buzz Aldrin flew on the Apollo 11 spacecraft piloted by Michael Collins. Armstrong and Aldrin set down the Eagle Lander on the Moon on July 20, 1969.

WHAT DID YOU THINK? Do we see all parts of the Moon’s surface at some time throughout the lunar cycle of phases? Do we see all parts of the Moon’s surface at some time throughout the lunar cycle of phases? No. Because the Moon’s rotation around Earth is synchronous, we always see the same side. The far side of the Moon has been seen only from spacecraft that pass or orbit it. No. Because the Moon’s rotation around Earth is synchronous, we always see the same side. The far side of the Moon has been seen only from spacecraft that pass or orbit it.

WHAT DID YOU THINK? Does the Moon rotate and, if so, how fast? Does the Moon rotate and, if so, how fast? The Moon rotates at the same rate that it revolves around Earth. If the Moon did not rotate, then, as it revolved, we would see its entire surface from Earth, which we do not. The Moon rotates at the same rate that it revolves around Earth. If the Moon did not rotate, then, as it revolved, we would see its entire surface from Earth, which we do not.

WHAT DID YOU THINK? What causes the ocean tides? What causes the ocean tides? The tides are created by orbital and gravitational forces, primarily from the Moon and, to a lesser extent, from the Sun. The tides are created by orbital and gravitational forces, primarily from the Moon and, to a lesser extent, from the Sun.

WHAT DID YOU THINK? When does the spring tide occur? When does the spring tide occur? Spring tides occur twice monthly, during each full and new Moon. Spring tides occur twice monthly, during each full and new Moon.