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Lecture Outlines
Physical Geology, 14/e
Plummer, Carlson & Hammersley
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The Earth’s Companions
Physical Geology 14/e, Chapter 23
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The Earth in Space
Earth – one of eight planets that orbit the Sun in
our solar system
Sun – has no solid surface, but rather is a huge
ball of very hot gas
• 75% H, 25% He
• overwhelming majority of mass in the solar
system is in the Sun
• hydrogen is fusing into helium in the core of
the Sun, releasing energy in the form of
sunlight
• gravity associated with Sun’s huge mass holds
planets, asteroids, and comets in their orbits
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The Solar System
All of the planets orbit the Sun in the same direction
• counterclockwise when viewed from above Earth’s north pole
Orbits of all planets lie within 7 degrees of the plane of Earth’s
orbit around the Sun
• solar system is distinctly disk-shaped
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The Solar System
Inner planets – small, rocky, include Mercury, Venus, Earth, Mars
Outer planets – huge, include Jupiter, Saturn, Uranus, Neptune
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Small Bodies in the Solar System
Asteroids – rocky or metallic objects, ~
1000 km or less in diameter
• most lie in the asteroid belt between the
orbits of Mars and Jupiter
Comets – icy bodies, ~1000 km or less in
diameter
•found in two reservoirs, the Kuiper Belt and the
Oort Cloud
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Origin of the Planets
Nebular hypothesis – the solar system
originated from a rotating, flattened disk of
gas and dust known as the solar nebula
• observed compositional trend from metal
and rock in the inner solar system, to
gases and ices in the outer solar system,
supports hypothesis
• Sun, Moon, Earth, and meteorites all
appear to have same age (about 4.6 billion
years) suggesting they formed in a single
event
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Formation of Planets & Moons
Planetesimals – formed from dust
clumped together which further clumped
into planets
• gravity drives process
• differentiation
Moons – originated by clumping of rings
of debris around planets or by gravitational
capture
Atmospheres – formed either by
gravitational capture of gases or from
volcanic eruptions and cometary impacts
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Earth’s Moon
Moon – Earth’s only natural satellite, possesses
no air, water or life, about ¼ the diameter of
Earth
• heavily cratered, ancient surface records
impact events for nearly the entire history of
the solar system
• lava flows and channels observed
• currently no volcanic, tectonic, or weathering
activity
• likely origin was catastrophic impact
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Mercury & Venus
Mercury – smallest inner planet, resembles Earth’s
Moon in both size and appearance
• no atmosphere
• density suggests very large iron core
• heavily cratered, but with smooth plains and scarps
Venus – hottest planetary surface in the solar system
(>480° C)
• CO2 atmosphere creates greenhouse effect
• abundant volcanoes and lava flows
• fractures and mountain belts suggest intense
tectonic activity
• relatively low number of impact craters suggests
recent or ongoing surface processes
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Mars
Mars – diameter 1/2 of Earth
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thin CO2 atmosphere (less 1% as thick as Earth’s)
red color results from oxidized iron-rich surface
frozen water and CO2 ice polar caps
abundant volcanoes and lava flows
fractures and canyons suggest tectonic activity
dune fields and dust storms indicate wind activity
eroded channels suggest flowing water in past
current conditions at surface not hospitable for life,
but evidence of flowing water in past suggests a
warmer and thicker atmosphere in ancient times
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Differences in the Terrestrial Planets
Show a progression of increasing geologic activity, both in the
past and today, directly related to their size
Water and ice more abundant on Earth and Mars
Biological processes on Earth produced oxygen-rich atmosphere
and abundant plants
• drastically affect surface conditions and weathering processes
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Jupiter
Jupiter – largest planet in the solar system
• composed of hydrogen and helium gases, with a
small ice/rock core
• atmospheric clouds are composed of methane,
ammonia and water ices
• high pressure deep in the interior, results in
hydrogen compressed first into liquid, then into a
liquid metal
• Jupiter’s largest moons: Europa, Ganymede, Io
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Saturn & Uranus
Saturn – second-largest planet in solar
system, composed of hydrogen and
helium gases, with small ice/rock core
• spectacular ring system of chunks of
ice and rock
• largest moon, Titan
Uranus – composed largely of hydrogen
and helium, with small rock/ice core
• rotational axis and moons’ orbits
tipped on side
• moon Miranda has unique landforms
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Neptune & Pluto
Neptune – similar in size and
composition to Uranus
• largest moon, Triton, has ice volcanoes
Pluto – recently demoted to dwarf planet
status
• largest icy object in solar system
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Asteroids, Comets, & Meteorites
Asteroids – small, rocky bodies that orbit
the Sun
•most lie in asteroid belt between orbits of Mars
and Jupiter
Meteorites – probably represent fragments
of asteroids
Comets – small, icy bodies that orbit the Sun
Giant impacts – periodically occur when
Earth sweeps up one of these remnants from
formation of the solar system
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End of Chapter 23
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