The document discusses the solar system from a broader perspective. It provides details on the formation of the solar system based on the nebular hypothesis, including how planets formed from a rotating cloud of gas and dust. It also describes the different types of objects in the solar system such as the terrestrial and gas planets, asteroids, comets, and Pluto. Additionally, it discusses theories for the origin of the Moon and evidence that Mars once had liquid water on its surface.

1. 2-1
Environmental
Geology
James Reichard
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 2-2
Chapter 2
Earth from a Larger
Perspective
NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

3. 2-3
The Solar System
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description

4. 2-4
The Sun
Average star
• Nuclear fusion of hydrogen and helium to
produce energy
• Hot dense center surrounded by an outer,
less dense atmosphere
• Releases electromagnetic radiation
a: Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams
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5. 2-5
The Planets
Terrestrial planets
• Have rocky surfaces
• Small
• Mercury, Venus, Earth and Mars
Gas planets
• Made up of gases, no solid surface
• Large
• Jupiter, Saturn, Uranus and Neptune

6. 2-6
Relative sizes
Lunar and Planetary Lab NASA
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7. 2-7
Pluto
• Demoted as a planet in 2006
The decision was made to define a planet as being large enough
that its gravity dominates its orbital path around the Sun, which
ultimately resulted in Pluto’s demotion.
• Rocky, cold and small
• New Horizons reached Pluto in 2015,
giving us our first detailed look at the
former planet.

8. 2-8
Comets and Asteroids
Comets
• Small, 1-10 km in diameter
• Rocky fragments in ice and frozen gases
• Highly elliptical orbits
© David Nunck/Science Photo LibraryGetty images
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Asteroids
• Mostly rock and metallic materials
• Most from asteroid belt between Jupiter and
Mars

9. 2-9
The Moon
• Earth’s only satellite
• Gravity controls tides
• Radiometric dating techniques proved that
the age of the Moon was similar to that of
the Earth.
NASA
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10. 2-10
Origin of the Solar System
Nebular Hypothesis
• Formed from rotating cloud of gas and dust
(nebula)
• Gases mainly hydrogen and helium
• Cloud contracted
• Higher temperatures and pressures
• Solid material formed, accretion
• Planetesimals, more accretion
• Planets

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Nebular Hypothesis
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12. 2-12
How Reliable is Nebular
Hypothesis?
• Most bodies rotate and revolve counter-
clockwise
• All bodies in same plane with solar
equator
• Most craters occurred early in the solar
system’s history
• Accretion disks have been found around
other stars

13. 2-13
Formation of the Moon
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14. 2-14
Other Stars in the Universe
• Our galaxy is the Milky Way
• Most bright points in the night sky are
galaxies
• The Big Bang Theory explains how the
universe was formed from a central
explosion

15. 2-15
Conceptual diagram illustrating the big
bang and the origin of the universe
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16. 2-16
The Milky Way
European Southern Observatory
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17. 2-17
Does Life Exist Beyond Earth?
Life on Earth
• Earth is 4.6 billion years old
• Life started in extreme conditions
• Extremophile bacteria
• Need liquid water
• Orbit in habitable zone
• Distance from sun or star that liquid water can
exist

18. 2-18
Habitable zones
b: © Brand X/PunchStock RF
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19. 2-19
Water on Mars
Data indicate that Mars was
much warmer and wetter
4.5 to 3.7 billion years ago,
resulting in an ancient ocean
that covered nearly 20% of
the planet’s surface.
What is the evidence?
NASA/JPL-Caltech/MSSS and PSI
NASA/JPL-Caltech/MSSS
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20. 2-20
Possible Intelligent Life
Rare Earth Hypothesis
• Energy output of sun fairly stable
• Earth’s processes help regulate CO2
• Jupiter ‘catches’ asteroids and comets
• Moon has reduced wobble of Earth’s axis

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Solar System Hazards
• Electromagnetic radiation
• Asteroid and comet impacts
Reto Stockli, NASA Earth Observatory; (inset): USGS
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22. 2-22
Meteor Crater and the K/T
boundary
USGS (a-b): Eleanor Camann
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23. 2-23
Mass extinctions
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Impacts
• Mesozoic/Cenozoic extinction event
(insert): Dr. Virgil L. Sharpton, University of Alaska Faribanks
• Recent impact on Jupiter
(a-b): NASA
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25. 2-25
Comet 67P/Churyumov-
Gerasimenko. Photo by ESA’s
Rosetta spacecraft.
It measures about 2.5
by 2.0 miles (4.1 by 3.2
km) along its widest
dimension.
ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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Gravitational effect of passing
planets
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27. 2-27
Avoiding Armageddon
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28. Appendix of Image Long
Descriptions

29. The Solar System Long Description
A. Planets within the solar system and their orbital paths around the Sun—not drawn to scale (asteroids
and asteroid belt not shown).
B. When the orbital paths are drawn to scale, one can begin to understand the vast distances between
those planets out beyond Mars.
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30. The Sun Long Description
The Sun’s immense gravity causes hydrogen atoms to undergo nuclear fusion (A) and form helium atoms—
image taken in ultraviolet light and color coded to appear gold. This nuclear reaction also releases a
continuous spectrum of wave energy (B), known as the electromagnetic
spectrum. Note that the peak energy output from the Sun lies in the visible part of the spectrum.
Electromagnetic energy travels outward from the Sun and provides much of the energy that drives the Earth
system.
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31. Relative sizes Long Description
When all the solar system bodies are shown at the same scale, one can see that the Sun is enormous
compared to the planets, particularly Earthand the other rocky planets of the inner sola+E7r system.
By compressing the distances between the planets, it becomes possible to view the relative size of the Sun
and planets at the proper scale. Note how much larger the outer (gas) planets are compared to the rocky
(terrestrial) planets of the inner solar system. The dwarf planet, Pluto, is shown on the far right. Images are
actual photos.
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32. Comets and Asteroids Long Description
A long tail develops from comet Hale-Bopp as it orbits around the Sun in 1997.
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33. The Moon Long Description
False-color image of the Moon taken by the Galileo spacecraft. Image processing created a color scheme
that reflects compositional variations in the rocks near the Moon’s surface. Reddish colors generally
correspond to older rocks that make up the more rugged lunar highlands, whereas the bluish colors
represent the younger rocks making up the flat lava flows of the maria, or lunar seas.
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34. Nebular Hypothesis Long Description
Illustration showing how the solar system evolved from a nebular cloud.
Collapsing nebula (A) increases in density and begins to rotate. Continued collapse (B) results in nuclear
fusion and the formation of a star, whereas the rotation forces the nebula to take on the shape of a disc.
Planetesimals develop by accretion of particles (C), while solar radiation drives off remaining parts of the
nebula. When the debris is cleared, what is left are planets (D) that lie in the same plane around the Sun
and revolve and rotate in the same counterclockwise manner.
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35. Formation of the Moon Long Description
The leading hypothesis for the origin of the Moon involves a Mars-sized impact (A) early in Earth’s history.
Some of the ejected material went into orbit around the Earth where it underwent accretion (B), forming the
Moon. Such a giant impact is also believed to have caused the young Earth to melt.
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36. Conceptual diagram illustrating the big bang
and the origin of the universe Long Description
Conceptual diagram illustrating the big bang and the origin of the universe. Galaxies we see today have been
rushing outward as an expanding sphere. The Hubble and other powerful telescopes are able to observe
distant features as they appeared nearly 13 billion years ago.
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37. The Milky Way Long Description
View looking down toward the central core of a clockwise-rotating galaxy. Our Sun lies on the outer band of
the Milky Way Galaxy, which is similar to the spiral galaxy shown here. Such galaxies are estimated to
contain hundreds of billions of stars.
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38. Habitable zones Long Description
Habitable zones are those regions of space where conditions are believed to be most favorable for the
development of life. Such zones can be defined in terms of areas where liquid water can exist around
individual stars (A), and also areas within a galaxy (B) where there is an abundance of heavier elements but
fewer cosmic hazards.
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39. Water on Mars Long Description
Coarse-grained sedimentary rock from Gale Crater (left) with a similar rock found on Earth (right). Based on
the fact that the gravel fragments are rounded and too large to be transported by wind, geologists conclude
that the fragments were carried by flowing water.
Sedimentary rock from Gale Crater showing crossbedding, which forms when wind or moving water causes
sediment layers to become oriented at an angle. By analyzing the way the layers accumulated here,
geologists can tell that the sediment was transported by running water as it entered a lake.
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40. Solar System Hazards Long Description
Approximately 190 impact sites have now been identified on Earth. Note that the number of impacts varies
across the globe, in part because of accessibility and the age of the rocks exposed at the surface. Also note
that very few impacts have been found in offshore areas. A 214-million-year-old impact structure in Canada
(inset) is believed to have had an original crater 50 to 60 miles (75-100 km) in diameter, formed by an
asteroid over 3 miles (5 km) in diameter. Some scientists believe this event may be linked to a mass
extinction in which nearly 60% of all species on the planet were lost.
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41. Meteor Crater and the K/T boundary Long Description
Meteor Crater in the Arizona desert formed approximately 50,000 years ago when a 150-foot (45-m) asteroid
struck the Earth. The crater is0.75 mile (1.2 km) in diameter.
Rock outcrop (A) near Trinidad, Colorado, that contains the boundary between rocks of the Cretaceous and
Tertiary periods of the Mesozoic and Cenozoic eras, respectively. Dinosaurs were dominant during the
Mesozoic, but went extinct when a large asteroid struck the Earth. Fallout from the impact created an
iridium-rich clay layer (B) found around the world, marking the boundary between the Cretaceous (K) and
Tertiary (T) periods, often referred to as the K/T boundary.
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42. Mass extinctions Long Description
Graph showing the number of species recorded in the fossil record over the last 600 million years of geologic
time. Mass extinctions are marked by periodic and sudden decreases in the numbers of families of species.
Scientists believe these die-offs are related to environmental changes that are global in nature.
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43. Impacts Long Description
The Chicxulub impact crater on the Yucatán peninsula in Mexico is one of the largest found on Earth, and the
impact that formed it is believed to be a major factor in the extinction of the dinosaurs. The crater measures
112 miles (180 km) across and was formed by an asteroid estimated to be 6.2 to 9.3 miles (10-15 km) in
diameter. A computer-generated gravity map (inset) indicates that the crater may be much larger, nearly
185 miles (300 km) across. In 2016, researchers began drilling into the inner ring of the crater to examine
the rocks and learn details of how life changed after the impact.
Image (A) taken by the Hubble space telescope of the broken fragments of comet Shoemaker-Levy 9 prior
to the 1994 impact with Jupiter. An infrared image (B) showing the impact plumes made by several of the
comet fragments.
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44. Comet 67P/Churyumov-Gerasimenko. Photo
by ESA’s Rosetta spacecraft. Long Description
Photo of comet 67P/Churyumov-Gerasimenko taken by the European Space Agency’s Rosetta spacecraft as it
orbited the comet in 2014. Rosetta also landed a probe on the comet’s surface, taking numerous
measurements and analyzing the comet’s composition. Comet 67P measures about 2.5 by 2.0 miles (4.1 by
3.2 km) along its widest dimension.
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45. Gravitational effect of passing planets Long Description
Asteroids and comets can be bumped from their normal orbits around the Sun by the gravitational effect of
passing planets, sending them across the orbital paths of the planets. Of particular concern are comets and
asteroids that cut across Earth’s orbit.
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46. Avoiding Armageddon Long Description
Technology already exists that would allow humans to alter the trajectory of an Earth-crossing object so that
it would miss the Earth. The ideal situation (A) is for a spacecraft to intercept the object while it is still far
from the Earth. In this situation only a slight change in its trajectory would be required to make it miss the
Earth. If the object is intercepted too close to the Earth (B), then the degree to which it would have to be
deflected would be beyond the capacity of humans.
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