Solution Manual For
Earth Portrait of a Planet 5th Edition by Stephen Marshak
All Chapters 1-23
CHAPTER 1
Cosmology and the Birth oƒ Earth
Learning Objectives
1. Students should be aware oƒ the Big Bang theory and the major evidence
supporting it. Distant galaxies are uniƒormly red-shiƒted rather than blue-
shiƒted; this implies that they are all moving away ƒrom us. The ƒarthest
galaxies are those that are most strongly red-shiƒted, meaning that they are
receding the ƒastest. Extrapolation oƒ 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 ƒusion reactors. Ƒor most oƒ their liƒe
histories (on the order oƒ billions oƒ years), hydrogen atoms are ƒused together
to ƒorm helium. Later stages in stellar evolution include ƒusion oƒ helium
atoms and other, heavier elements; ultimately, iron is the heaviest element
that can be produced through ƒusion reactions within stars.
3. Aƒter their cycles oƒ ƒusion are complete, large stars violently explode (ƒorming
supernovae), producing elements heavier than iron and leaving behind a
, residue oƒ diƒƒuse nebulae, which may be recycled to ƒorm a new star at some
point in the ƒuture.
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
, same direction (counterclockwise as viewed ƒrom above Earth’s North Pole).
These ƒacts imply simultaneous planetary ƒormation ƒrom a swirling nebula
surrounding the Sun (the similarities in orbits would then be a natural result oƒ
conservation oƒ angular momentum). The planets accreted ƒrom 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 oƒ
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 ƒrom debris accumulated when a protoplanet collided with
Earth approximately 4.3 Ga.
Summary ƒrom the Text
The geocentric model placed Earth at the center oƒ 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 oƒ Earth in ancient times, but it was
not until ƒairly 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.
The Earth is one oƒ eight planets orbiting the Sun, and this Solar System lies on
the outer edge oƒ a slowly revolving galaxy, the Milky Way, which is composed oƒ
about 300 billion stars. The Universe contains at least hundreds oƒ billions oƒ
galaxies.
The red shiƒt oƒ light ƒrom distant galaxies, a maniƒestation oƒ the Doppler eƒƒect,
indicates that all distant galaxies are moving away ƒrom Earth. This observation leads
, to the expanding Universe theory. Most astronomers agree that this expansion began
aƒter the Big Bang, a cataclysmic explosion about 13.7 billion years ago.
The ƒirst atoms (hydrogen and helium) oƒ the Universe developed within minutes
oƒ the Big Bang. These atoms ƒormed vast gas clouds, called nebulae.
Gravity caused clumps oƒ gas in the nebulae to coalesce into revolving balls. As
these balls oƒ gas collapsed inward, they evolved into ƒlattened disks with bulbous
centers. The protostars at the center oƒ these disks eventually became dense and
suƒƒiciently hot that ƒusion reactions began within them. When this happened, they
became true stars, emitting heat and light.
Heavier elements ƒorm during ƒusion reactions in stars; the heaviest are mostly
made during supernova explosions. Earth and the liƒe ƒorms on it contain elements
that could have only been produced during the liƒe cycle oƒ stars. Thus, we are all
made oƒ stardust.
According to the nebular theory oƒ planet ƒormation, planets developed ƒrom the
rings oƒ gas and dust surrounding protostars. The gas and dust condensed into
planetesimals, which then clumped together to ƒorm protoplanets and ƒinally true
planets. Inner rings became the terrestrial planets; outer rings grew into giant
planets.
The Moon ƒormed ƒrom debris ejected when a protoplanet collided with Earth in
the young Solar System.
A planet assumes a near-spherical shape when it becomes so soƒt 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 ƒixed with respect to one
another as viewed ƒrom Earth. As Earth and the other planets traverse through their
orbits around the Sun, the positions oƒ the planets vary with respect to the “ƒixed”
celestial sphere.
Earth Portrait of a Planet 5th Edition by Stephen Marshak
All Chapters 1-23
CHAPTER 1
Cosmology and the Birth oƒ Earth
Learning Objectives
1. Students should be aware oƒ the Big Bang theory and the major evidence
supporting it. Distant galaxies are uniƒormly red-shiƒted rather than blue-
shiƒted; this implies that they are all moving away ƒrom us. The ƒarthest
galaxies are those that are most strongly red-shiƒted, meaning that they are
receding the ƒastest. Extrapolation oƒ 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 ƒusion reactors. Ƒor most oƒ their liƒe
histories (on the order oƒ billions oƒ years), hydrogen atoms are ƒused together
to ƒorm helium. Later stages in stellar evolution include ƒusion oƒ helium
atoms and other, heavier elements; ultimately, iron is the heaviest element
that can be produced through ƒusion reactions within stars.
3. Aƒter their cycles oƒ ƒusion are complete, large stars violently explode (ƒorming
supernovae), producing elements heavier than iron and leaving behind a
, residue oƒ diƒƒuse nebulae, which may be recycled to ƒorm a new star at some
point in the ƒuture.
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
, same direction (counterclockwise as viewed ƒrom above Earth’s North Pole).
These ƒacts imply simultaneous planetary ƒormation ƒrom a swirling nebula
surrounding the Sun (the similarities in orbits would then be a natural result oƒ
conservation oƒ angular momentum). The planets accreted ƒrom 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 oƒ
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 ƒrom debris accumulated when a protoplanet collided with
Earth approximately 4.3 Ga.
Summary ƒrom the Text
The geocentric model placed Earth at the center oƒ 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 oƒ Earth in ancient times, but it was
not until ƒairly 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.
The Earth is one oƒ eight planets orbiting the Sun, and this Solar System lies on
the outer edge oƒ a slowly revolving galaxy, the Milky Way, which is composed oƒ
about 300 billion stars. The Universe contains at least hundreds oƒ billions oƒ
galaxies.
The red shiƒt oƒ light ƒrom distant galaxies, a maniƒestation oƒ the Doppler eƒƒect,
indicates that all distant galaxies are moving away ƒrom Earth. This observation leads
, to the expanding Universe theory. Most astronomers agree that this expansion began
aƒter the Big Bang, a cataclysmic explosion about 13.7 billion years ago.
The ƒirst atoms (hydrogen and helium) oƒ the Universe developed within minutes
oƒ the Big Bang. These atoms ƒormed vast gas clouds, called nebulae.
Gravity caused clumps oƒ gas in the nebulae to coalesce into revolving balls. As
these balls oƒ gas collapsed inward, they evolved into ƒlattened disks with bulbous
centers. The protostars at the center oƒ these disks eventually became dense and
suƒƒiciently hot that ƒusion reactions began within them. When this happened, they
became true stars, emitting heat and light.
Heavier elements ƒorm during ƒusion reactions in stars; the heaviest are mostly
made during supernova explosions. Earth and the liƒe ƒorms on it contain elements
that could have only been produced during the liƒe cycle oƒ stars. Thus, we are all
made oƒ stardust.
According to the nebular theory oƒ planet ƒormation, planets developed ƒrom the
rings oƒ gas and dust surrounding protostars. The gas and dust condensed into
planetesimals, which then clumped together to ƒorm protoplanets and ƒinally true
planets. Inner rings became the terrestrial planets; outer rings grew into giant
planets.
The Moon ƒormed ƒrom debris ejected when a protoplanet collided with Earth in
the young Solar System.
A planet assumes a near-spherical shape when it becomes so soƒt 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 ƒixed with respect to one
another as viewed ƒrom Earth. As Earth and the other planets traverse through their
orbits around the Sun, the positions oƒ the planets vary with respect to the “ƒixed”
celestial sphere.
