Solutions Manual for Earth Portrait of a Planet, 5th edition by Stephen Marshak All Chapters 1 to 23 complete Verified editon ISBN: 9780393937503
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Solutions Manual for Earth Portrait of a Planet, 5th edition
by Stephen Marshak (All Chapters) A+
CHAPTER 1
Cosmology and the Birth of Earth
Learning Objectives
1. Students should be aware of the Big Bang theory and the major evidence supporting it.
Distant galaxies are uniformly red-shifted rather than blue- shifted; this implies that they are all
moving away from us. The farthest galaxies are those that are most strongly red-shifted, meaning
that they are receding the fastest. Extrapolation of velocities and trajectories into the past
suggests that all matter in the Universe was contained in a single point, approximately 13.7
billion years ago. At that time, the Universe explosively came into existence.
2. Stars, including our Sun, are nuclear fusion reactors. For most of their life histories (on
the order of billions of years), hydrogen atoms are fused together to form helium. Later stages in
stellar evolution include fusion of helium atoms and other, heavier elements; ultimately, iron is
the heaviest element that can be produced through fusion reactions within stars.
3. After their cycles of fusion are complete, large stars violently explode (forming
supernovae), producing elements heavier than iron and leaving behind a residue of diffuse
nebulae, which may be recycled to form a new star at some point in the future.
4. Our Solar System is approximately 4.57 Ga (billion years old). All eight planets revolve
around the Sun in coplanar, elliptical orbits. All planets orbit in the
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same direction (counterclockwise as viewed from above Earth’s North Pole). These facts imply
simultaneous planetary formation from a swirling nebula surrounding the Sun (the similarities in
orbits would then be a natural result of conservation of angular momentum). The planets
accreted from this nebula through gravitational attraction and haphazard collisions. Pluto, long
considered the “ninth planet,” has seen its status demoted; astronomers now
recognize eight major planets.
5. The terrestrial planets (Mercury, Venus, Earth, and Mars) are relatively small, dense, and
rocky worlds. The giant planets are predominantly composed of the light gases hydrogen and
helium (Jupiter and Saturn) or ices (Uranus and Neptune); they are much larger and much less
dense than the terrestrial planets.
6. Our Moon is chemically similar to the Earth’s mantle. The Moon is thought to have
originated from debris accumulated when a protoplanet collided with Earth approximately 4.3
Ga.
Summary from the Text
The geocentric model placed Earth at the center of the Universe, with the planets and Sun
orbiting around the Earth within a celestial sphere speckled with stars. The heliocentric model,
which gained acceptance during the Renaissance, placed the Sun at the center.
Eratosthenes was able to measure the size of Earth in ancient times, but it was not until fairly
recently that astronomers accurately determined the distances to the Sun, planets, and stars.
Distances in the Universe are so large that they must be measured in light-years.
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The Earth is one of eight planets orbiting the Sun, and this Solar System lies on the outer edge of
a slowly revolving galaxy, the Milky Way, which is composed of about 300 billion stars. The
Universe contains at least hundreds of billions of galaxies.
The red shift of light from distant galaxies, a manifestation of the Doppler effect, indicates that
all distant galaxies are moving away from Earth. This observation leads
to the expanding Universe theory. Most astronomers agree that this expansion began after the
Big Bang, a cataclysmic explosion about 13.7 billion years ago.
The first atoms (hydrogen and helium) of the Universe developed within minutes of the Big
Bang. These atoms formed vast gas clouds, called nebulae.
Gravity caused clumps of gas in the nebulae to coalesce into revolving balls. As these balls of
gas collapsed inward, they evolved into flattened disks with bulbous centers. The protostars at
the center of these disks eventually became dense and sufficiently hot that fusion reactions began
within them. When this happened, they became true stars, emitting heat and light.
Heavier elements form during fusion reactions in stars; the heaviest are mostly made during
supernova explosions. Earth and the life forms on it contain elements that could have only been
produced during the life cycle of stars. Thus, we are all made of stardust.
According to the nebular theory of planet formation, planets developed from the rings of gas and
dust surrounding protostars. The gas and dust condensed into planetesimals, which then clumped
together to form protoplanets and finally true planets. Inner rings became the terrestrial planets;
outer rings grew into giant planets.
The Moon formed from debris ejected when a protoplanet collided with Earth in the young Solar
System.
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A planet assumes a near-spherical shape when it becomes so soft that gravity can smooth out
irregularities.
Answers to Review Questions
1. Why do the planets appear to move with respect to the stars?
ANS: Stars are so relatively distant that they appear fixed with respect to one another as viewed
from Earth. As Earth and the other planets traverse through their orbits around the Sun, the
positions of the planets vary with respect to the “fixed” celestial sphere.
2. Contrast the geocentric and heliocentric Universe concepts.
ANS: The geocentric concept placed Earth at the center of the Universe, with the Sun and the
other planets revolving around it. The heliocentric concept placed the Sun at the center, with
Earth and the other planets revolving around it.
3. Describe how Foucault’s Pendulum demonstrates that Earth is rotating on its
axis.
ANS: Foucault set forth a heavy pendulum and observed its long-term behavior. Slowly but
surely the swing path of the pendulum appeared to rotate about a vertical axis. According to the
property of inertia, unless a new force is added, the pendulum will maintain its swinging plane.
Foucault concluded correctly that Earth must have rotated in order for the plane to appear to have
changed in this manner.
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