Dtu10e lecture ppt_ch06

In this chapter, you will discover…In this chapter, you will discover…

why Earth is such an ideal environment for lifewhy Earth is such an ideal environment for life that Earth is constantly in motion inside and outthat Earth is constantly in motion inside and out how Earth’s magnetic field helps protect ushow Earth’s magnetic field helps protect us what made the craters on the Moonwhat made the craters on the Moon how the Sun and the Moon cause Earth’s tideshow the Sun and the Moon cause Earth’s tides that Earth and the Moon each have two (different) major that Earth and the Moon each have two (different) major

types of surface featurestypes of surface features that water ice has been found on the Moonthat water ice has been found on the Moon

Temperature Profile of Earth’s Atmosphere

The atmospheric temperature changes with altitude because of the way sunlight and heat from Earth’s surface interact with various gases at different heights.

The atmosphere plays a key role in sustaining The atmosphere plays a key role in sustaining life on Earth.life on Earth.

It is believed, Earth is on its third atmosphere. It is believed, Earth is on its third atmosphere. The first atmosphere was composed of trace The first atmosphere was composed of trace

remnants of hydrogen and helium left over from remnants of hydrogen and helium left over from the formation of the solar system.the formation of the solar system.

The second atmosphere came from inside the The second atmosphere came from inside the Earth, vented through volcanoes and cracks in Earth, vented through volcanoes and cracks in its surface. It was composed primarily of carbon its surface. It was composed primarily of carbon dioxide, water vapor, and nitrogen.dioxide, water vapor, and nitrogen.

The third atmosphere is composed mostly of The third atmosphere is composed mostly of nitrogen and oxygen.nitrogen and oxygen.

Earth’s Atmosphere

Earth’s Dynamic Oceans

This image shows the relative size of Earth compared to a sphere containing all of Earth’s water. The sphere is about 860 miles in diameter and includes freshwater, oceans, ice, and even water in the atmosphere. Nearly three-quarters of Earth’s surface is covered with water, a substance that is essential to the existence of life. In contrast, there is no liquid water at all on the surfaces of Mercury, Venus, Mars, or the Moon.

Liquid water is believed to have precipitated out of Liquid water is believed to have precipitated out of Earth’s second atmosphere and from impacts of Earth’s second atmosphere and from impacts of water-rich space debris forming the oceans.water-rich space debris forming the oceans.

The oceans eventually soaked up about half the The oceans eventually soaked up about half the carbon dioxide in the second atmosphere, as rain carbon dioxide in the second atmosphere, as rain absorbed it from the air and carried it earthward.absorbed it from the air and carried it earthward.

Carbon dioxide combined with water in the early Carbon dioxide combined with water in the early ocean forming clays, shales, and coral. As the ocean forming clays, shales, and coral. As the material settled to the ocean floor, it eventually material settled to the ocean floor, it eventually formed limestones removing carbon dioxide from formed limestones removing carbon dioxide from the atmosphere. the atmosphere.

Ocean Formation and the Changing Atmosphere

The Greenhouse Effect in a Car

The glass windows in this car allow visible light to enter but prevent theinfrared radiation released by the car’s interior from escaping. The infrared, therefore, heats the air in the car much higher than the outside air. This effect is used to advantage in greenhouses and is why it is called the greenhouse effect.

The Greenhouse Effect

Sunlight and heat from Earth’s interior warm Earth’s surface, which inturn radiates energy, mostly as infrared radiation. Much of this radiation is absorbed by atmospheric carbon dioxide and water, heating the air, which in turn increases Earth’s temperature even further. In equilibrium, Earth radiates as much energy as it receives.

The Greenhouse Effect

The amount of carbon dioxide in our atmosphere since 1000 A.D. has been determined. The increase in carbon dioxide since 1800 due to burning fossil fuels and decreases in forestation have caused a dramatic temperature increase.

The surface of Earth, or the crust, is made of less-dense rock floating on a layer of denser material.

The theory of Plate Tectonics indicates the crust has three types of boundaries, suggesting each continent makes up separate plates.

Shown here is an artist’s rendition of one such boundary, a mountain range in the middle of the ocean floor, called the Mid-Atlantic Ridge.

The Mid-Atlantic Ridge

The present continents are pieces of what was once a bigger, united body called Pangaea.

The Supercontinent Pangaea


Geologists believe that Pangaea must have first split into two smaller supercontinents, which they call Laurasia and Gondwana.


These bodies later separated into the continents of today. Gondwana split into Africa, South America, Australia, and Antarctica, while Laurasia divided to become North America and Eurasia.

Earth’s Major Tectonic Plates

Earth’s surface is divided into a dozen or so rigid plates that move relative to one another. The boundaries of the plates are the scenes of violent seismic and geologic activity, such as earthquakes, volcanoes, rising mountain ranges, and sinking seafloors. The arrows indicate whether plates are moving apart (←→), together (→←), or sliding past one another (↑↓).

The boundaries between tectonic plates are the sites of The boundaries between tectonic plates are the sites of some of the most impressive geological activity on our some of the most impressive geological activity on our planet.planet.

Most of the earthquakes and volcanoes are found at Most of the earthquakes and volcanoes are found at plate boundaries.plate boundaries.

Divergent boundaries are located where plates move Divergent boundaries are located where plates move apart forming features like the Mid-Atlantic Ridge.apart forming features like the Mid-Atlantic Ridge.

Convergent boundaries are located where plates come Convergent boundaries are located where plates come together forming features like the Himalayas.together forming features like the Himalayas.

Transform boundaries are located where plates slide Transform boundaries are located where plates slide grind past each others forming features like the San grind past each others forming features like the San Andreas Fault Zone. Andreas Fault Zone.

Plate Boundaries

Planetary Differentiation as Earth Formed Planetary Differentiation as Earth Formed

Early Earth was initially a homogeneous mixture of elements with no continents or oceans. (a) Molten iron sank to the center and light material floated upward to form a crust. (b) As a result, Earth has a dense iron core and a crust of light rock, with a mantle of intermediate density between them.

Heat supplied by the heating coil warms the water at the bottom of the pot. The heated water consequently expands, decreasing its density. This lower-density water rises (like bubbles in soda) and transfers its heat to the cooler surroundings. When the hot, rising water gets to the top of the pot, it loses a lot of heat into the room, becomes denser, and sinks back to the bottom of the pot to repeat the process.

Convection

Mechanism of Plate Tectonics

Convection currents in Earth’s interior are responsible for pushing around rigid plates on its crust. New crust forms in oceanic rifts, where magma oozes upward between separating plates. Mountain ranges and deep oceanic trenches are formed where plates collide and crust sometimes sinks back into the interior. Note that not all tectonic plates move together or apart—some scrape against each other.

Earth’s Magnetic Field

(a) The magnetic field of a bar magnet is revealed by the alignment of iron filings on paper. (b) Although Earth does not contain a bar magnet, its rotation, combined with moving electric charges in its core, creates an equivalent field. Note that the field is not aligned with Earth’s rotation axis. By convention, the magnetic pole near Earth’s north rotation axis is called the magnetic north pole even though it is actually the south pole on a magnet! We will see similar misalignments and flipped magnetic fields when we study other planets.

Earth’s Magnetosphere

A slice through Earth’s magnetic field, which surrounds the entire planet, carves out a cavity in space that excludes charged particles ejected from the Sun, called the solar wind. Most of the particles of the solar wind are deflected around Earth by the fields in a turbulent region colored blue in this drawing. Because of the strength of Earth’s magnetic field, our planet traps some charged particles in two huge, doughnut-shaped rings called the Van Allen belts (in red).

The Northern Lights (Aurora Borealis)

A deluge of charged particles from the Sun can overload the Van Allen belts and cascade toward Earth, producing auroras that can be seen over a wide range of latitudes. View of an aurora from Polar spacecraft imposed on a graphic image of Earth. Colors from blue to red indicate lowest to highest auroral activity. Auroras typically occur 100 to 400 km above Earth’s surface.


View of aurora over the north central part of the United States and southern Canada as seen from the International Space Station when it was over south central Nebraska.


This is the Aurora borealis in Alaska. The gorgeous aurora seen here is mostly glowing green due to emission by oxygen atoms in our atmosphere. Some auroras remain stationary for hours, while others shimmer, like curtains blowing in the wind.

(a) This photograph, taken from lunar orbit by astronauts, includes the crater Aristillus. Note the crater’s central peaks, the collapsed, terraced crater wall, and the ejecta blanket. Numerous smaller craters resulting from the same impact pockmark the surrounding lunar surface. The following three drawings show the crater formation process. (b) An incoming meteoroid, (c) upon impact, is pulverized and the surface explodes outward and downward. (d) After the impact, the ground rebounds, creating the central peak and causing the crater walls to collapse. The lighter region is the ejecta blanket.

Lunar Craters

Shallow Angle Impact Crater

This crater, in Mare Nubium, is the result of a very low-angle impact. Despite the missing ejecta between the two lines, the impact crater is still circular, indicating how powerful the impact was. The impacting body came from the direction of the missing ejecta.

A Microscopic Lunar Crater

This photograph, taken through a microscope, shows tiny microcraters less than 1 mm across on a piece of Moon rock.

Mare Imbrium and the Surrounding Highlands

Mare Imbrium, the largest of the 14 dark plains that dominate the Earth-facing side of the Moon, is ringed by lighter-colored highlands strewn with craters and towering mountains. The highlands were created by asteroid impacts pushing land together.

Details of a Lunar Mare

Close-up views of the lunar surface reveal rilles and numerous small craters on the maria. Astronauts in lunar orbit took this photograph of Mare Tranquillitatis (Sea of Tranquility) in 1969 while searching for potential landing sites for the first human landing. At 1100 km (700 mi) across, this mare is the same size as the distance from London to Rome or Chicago to Philadelphia.


Astronaut David Scott on Hadley’s rille during the Apollo 15 mission to the Moon.

Possible lava tube outlet on the Moon imaged by NASA’s Lunar Reconnaissance Observer.


Bridge near King crater. We know this is a bridge, rather than two depressions because sunlight, coming from the lower right, is visible in the upper left depression.


The Far Side of the Moon

Unlike the side of the Moon facing Earth, the lunar far side has only a few, small maria. It is almost entirely covered with highlands.

An Apollo Astronaut on the Moon

Apollo 17 astronaut Harrison Schmitt enters the Taurus-Littow Valley on the Moon. The enormous boulder seen here slid down a mountain to the right of this image, fracturing on the way. This final Apollo mission landed in the most rugged terrain of any Apollo flight.

The Moon’s surface is covered by a layer of (a) powdered rock and (b) small pieces of rock. Called regolith, the powdered rock was created over billions of years as a result of bombardment by space debris; it sticks together like wet sand, as illustrated by this Apollo 11 astronaut bootprint.

The Regolith

Mare Basalt

This 1.53-kg (3.38-lb) specimen of mare basalt was brought back by Apollo 15 astronauts in 1971. Small holes that cover about a third of its surface suggest that gas was dissolved in the lava from which this rock solidified. When the lava reached the airless lunar surface, bubbles formed as the pressure dropped and the gas expanded. Some of the bubbles were frozen in place as the rock cooled.

Anorthosite

The lunar highlands are covered with this ancient type of rock, which is believed to be the material of the original lunar crust. This sample’s dimensions are 18 × 16 × 7 cm. Although this sample is medium gray, other anorthosites retrieved from the Moon have been white, while others are darker gray than this one. This one was brought back by Apollo 16 astronauts.

Impact Breccias

These rocks are created from shattered debris fused together under high temperature and pressure. Such conditions prevail immediately following impacts of space debris on the Moon’s surface.

Apollo 11 Landing Site

On the Moon’s Sea of Tranquility, Astronaut Buzz Aldrin stands next to the package of equipment containing the seismic detector. The corner reflectors are used, even today, to determine the distance from Earth to the Moon. The stereo camera took pairs of images of the Moon’s surface. Seeing them through special glasses gives a 3-D close-up view of the Moon’s surface. The bottom half of the lander is still on the Moon’s surface. The top half brought astronauts Neil Armstrong and Buzz Aldrin back into lunar orbit, where they transferred to the command module to fly home.

As the Moon’s interior shrank, the surfacesettled irregularly, creating long lines of cliffs called scarps.

Seismic experiments revealed that the main regions of the Moon’s interior mimic those of Earth, but in different proportions.

Water ice may exist in the polar craters, where the energy received from the Sun is insufficient to melt it.

• Based on data gathered from Moon rocks and other sources, the collision-ejection theory seems to be the best explanation for the Moon’s formation.

• This computer simulation models the creation of the Moon from material ejected by the impact of a large planetlike body with the young Earth.

Collision-Ejection Theory

The collision that created the Moon could have also knocked Earth’s rotation axis over so that today it has a 23½° tilt, thereby creating the seasons.

Motion of Earth-Moon System

(b) Analogously, this time-lapse image shows a pair of different-mass disks connected by a piece of wood sliding across a table. Note that the center of mass of this collection of objects moves in a straight line, while its other parts follow curved paths. As with the Earth–Moon system, the center of mass is closer to the more massive disk than to the less massive one.

(a) The paths of Earth and the Moon as their barycenter follows an elliptical orbit around the Sun.

Synchronous Rotation of the Moon

This is the motion of the Moon around Earth as seen from above Earth’s north polar region (ignoring Earth’s orbit around the Earth-Moon barycenter). For the Moon to keep the same side facing Earth as it orbits our planet, the Moon must rotate on its axis at precisely the same rate that it revolves around Earth.

Tidal Forces

(a) The Moon induces tidal forces on Earth. At each point, this force is the difference between the force, Fout, created by the orbital motion of the two bodies around their barycenter, and the Moon’s gravitational force, Fgrav, at that point. The magnitude and direction of each arrow represent the strength and direction of each force. (b) Water slides along Earth to create the tides. Ignoring Earth’s rotation and the effects of the continents, this figure shows how two high tides are created on Earth by the Moon’s gravitational pull. The Sun has a weaker, but otherwise identical, effect.

During new and full moon phases, the Sun’s gravitation boosts the tidal bulges in the same direction as the Moon, creating larger spring tides. During the quarter moon phases, the

Sun pulls the tidal bulges in a different direction from the Moon, diminishing the tides. These are called neap tides.

Tides on Earth

Lunar Ranging

Beams of laser light are fired through three telescopes at the Observatoire de la Côte d’Azur, France. The light is then reflected back by the corner reflectors placed on the Moon by Apollo astronauts. From the time it takes the light to reach the Moon and return to Earth, astronomers can determine the distance to the Moon to within a few millimeters.

Summary of Key IdeasSummary of Key Ideas

Earth: A Dynamic, Vital World Earth’s atmosphere is about four-fifths nitrogen and one-fifth oxygen. Earth’s atmosphere is about four-fifths nitrogen and one-fifth oxygen.

This abundance of oxygen is due to the biological processes of life-This abundance of oxygen is due to the biological processes of life-forms on the planet.forms on the planet.

Earth’s atmosphere is divided into layers named the troposphere, Earth’s atmosphere is divided into layers named the troposphere, stratosphere, mesosphere, and ionosphere.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 The outermost layer, or crust, of Earth offers clues to the history of our

planet.planet. Earth’s surface is divided into huge plates that move over the upper Earth’s surface is divided into huge plates that move over the upper

mantle. Movement of these plates, a process called plate tectonics, is mantle. Movement of these plates, a process called plate tectonics, is caused by convection in the mantle. Also, upwelling of molten material caused by convection in the mantle. Also, upwelling of molten material along cracks in the ocean floor occurs during seafloor spreading. Plate along cracks in the ocean floor occurs during seafloor spreading. Plate tectonics is responsible for most of the major features of Earth’s tectonics is responsible for most of the major features of Earth’s surface, including mountain ranges, volcanoes, and the shapes of the surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans.continents and oceans.

Study of seismic waves (vibrations produced by earthquakes) Study of seismic waves (vibrations produced by earthquakes) shows that Earth has a small, solid inner core surrounded by a shows that Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin, low-density crust mantle, which in turn is surrounded by the thin, low-density crust on which we live. Earth’s inner and outer cores are composed on which we live. Earth’s inner and outer cores are composed primarily of iron. The mantle is composed of iron-rich minerals.primarily of iron. The mantle is composed of iron-rich minerals.

Earth’s magnetic field produces a magnetosphere that surrounds Earth’s magnetic field produces a magnetosphere that surrounds the planet and deflects the solar wind.the planet and deflects the solar wind.

Some charged particles from the solar wind are trapped in two Some charged particles from the solar wind are trapped in two huge, doughnut-shaped rings called the Van Allen radiation huge, doughnut-shaped rings called the Van Allen radiation belts. An Earthward deluge of particles from a coronal mass belts. An Earthward deluge of particles from a coronal mass ejection on the Sun can pierce the belts and produce exceptional ejection on the Sun can pierce the belts and produce exceptional auroras.auroras.

Earth: A Dynamic, Vital World

The Moon and Tides The Moon has heavily cratered highlands and relatively smooth-The Moon has heavily cratered highlands and relatively smooth-

surfaced maria. surfaced maria. Impacts have been the only significant Impacts have been the only significant ““weatheringweathering”” agent on the agent on the

Moon; the Moon’s regolith (pulverized rock layer) was formed by Moon; the Moon’s regolith (pulverized rock layer) was formed by meteoritic action.meteoritic action.

Lunar rocks brought back to Earth contain no water and are depleted Lunar rocks brought back to Earth contain no water and are depleted of volatile elements.of volatile elements.

Powdered into regolith, the anorthosite rock of the highland is brighter Powdered into regolith, the anorthosite rock of the highland is brighter than the powdered basalt of the maria.than the powdered basalt of the maria.

Many lunar rock samples are solidified lava formed largely of minerals Many lunar rock samples are solidified lava formed largely of minerals also found in Earth rocks.also found in Earth rocks.

Anorthositic rock in the lunar highlands was formed between 4.0 and 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 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 and 3.8 billion years ago. The Moon’s surface has undergone very little geologic change over the past 3 billion years.little geologic change over the past 3 billion years.

The Moon and Tides Frozen water has been discovered in numerous places just below Frozen water has been discovered in numerous places just below

the Moon’s surface.the Moon’s surface. The collision-ejection theory of the Moon’s origin, accepted by The collision-ejection theory of the Moon’s origin, accepted by

most astronomers, holds that the young Earth was struck by a most astronomers, holds that the young Earth was struck by a huge planetesimal, and debris from this collision coalesced to form huge planetesimal, and debris from this collision coalesced to form the Moon.the Moon.

The Moon was molten in its early stages, and the anorthositic The Moon was molten in its early stages, and the anorthositic crust solidified from low-density magma that floated to the lunar crust solidified from low-density magma that floated to the lunar surface. The mare basins were created later by the impact of surface. The mare basins were created later by the impact of planetesimals and were then filled with lava from the lunar interior.planetesimals and were then filled with lava from the lunar interior.

Gravitational interactions between Earth and the Moon produce Gravitational interactions between Earth and the Moon produce tides in the oceans of Earth and set the Moon into synchronous tides in the oceans of Earth and set the Moon into synchronous rotation. The Moon is moving away from Earth, and consequently, rotation. The Moon is moving away from Earth, and consequently, Earth’s rotation rate is decreasing.Earth’s rotation rate is decreasing.

Key TermsKey Termsanorthositecapture theorycocreation theorycollision-ejection theorycontinental driftconvectioncore (of Earth)crustdynamo theoryejecta blanketfission theoryhighlands

impact brecciasionosphere (thermosphere)mantlemare (plural maria)mare basaltmasconsmesosphereneap tidenorthern lights (aurora borealis)ozone layerplanetary differentiationplate tectonics

regolithrillescarpsseafloor spreadingseismic wavesseismographsouthern lights (aurora australis)spring tidestratospheresynchronous rotationtroposphereVan Allen radiation belts

Science

Dtu10e lecture ppt_ch06