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Test 2 on Chapters 7-11 will be this Wed 5/21.
Review will be tomorrow.
Astronomy 04
The Solar System
Chapter 20:
“Planet Earth”
Four Stages of Planetary Formation:
• Condensation
• Accretion
• Planetesimals
• Protoplanet
Four Stages of Planetary Development:
• Differentiation
• Cratering
• Flooding
• Surface Evolution
Differentiation
Early in Earth’s history when it was still totally
molten, materials separated according to density.
Metals such as iron (Fe) and nickel (Ni) sank to
the center while light rocky materials like silicates
(Si) floated to the surface.
Cratering
After Earth had cooled and a crust had formed, a
heavy bombardment of planetesimals and
meteorites blasted its surface forming craters.
Flooding
Molten lava flowed through cracks in Earth’s crust
produced by planetesimal impacts.
Huge amounts of vapor in the atmosphere condensed and
torrential rains fell, drained off the continents and formed
the first oceans.
Slow Surface Evolution
Air and water erosion
along with shifting
continental plates
constantly changed the
appearance of Earth over
the last 3.5 billion years.
Earth is a unique planet in
many ways:
• Life exists on Earth
surface.
• Earth has large amounts of
liquid water on its surface.
• Earth has oxygen in its
atmosphere.
Earth is a unique planet in
many ways:
• Earth surface is constantly
being renewed through the
process of Plate Tectonics.
Earth’s magnetic field
protects it from the solar
wind.
The rotation of Earth’s
highly-conductive iron
nickel core generate the
magnetic field in a process
called the dynamo effect.
Chapter 20: “Planet Earth”
Earth’s magnetic field
protects it from the solar
wind.
The surface where the solar
wind is first deflected by
Earth’s magnetic field is
called the bow shock.
The cavity in the solar wind
generated by Earth’s
magnetic field is called the
magnetosphere.
High energy particles from
the solar wind trapped
within the magnetosphere
produce the Van Allen
belts.
The magnetic field of Earth
acts with the solar wind to
produce the colorful
aurora.
The crust of Earth is broken
up into huge pieces called
plates.
The theory that deals with the
origin and motion of these
plates is called plate
tectonics.
The huge cracks in Earth’s
crust that separate plates
are called faults.
Here we see the famous San
Andreas fault which runs
just to our west through
the Santa Cruz Mountains.
The plates consist of the crust and the uppermost layers of
Earth’s mantle which together form the lithosphere.
At the bottom of the lithosphere – 100 km down – we find
the mantle,
The mantle, although solid, is highly elastic. The plates
“float” and move on the mantle.
Plates are formed along regions called “midocean rifts” where
lava wells up from below.
Near the rifts, Earth’s crust is pulling apart at the rate of 2-4
cm per year.
In other places, sections of the crust are pushed below the
continents into subduction zones. This process builds
mountains and volcanoes.
Rocks that form near the
the midcoean rifts are
solidified lava called
basalts.
One of the marks of plate
tectonics is folded
mountain chains.
Crustal plates can also
split apart to open new
seas. The first sign of such
splitting is a long, straight,
deep depression called a
rift valley.
About 250 million years ago all continents belonged to a
single land mass called Pangea.
Gradually the plates drifted apart from each other forming
the land masses we know today.
The first atmosphere of Earth called the primeval
atmosphere consisted of hydrogen, helium, methane and
ammonia.
A secondary atmosphere was formed as Earth cooled
through the process of outgassing. It consisted of carbon
dioxide and water vapor.
When plant life appeared on Earth, carbon dioxide was
oxygen was produced through the process of
photosynthesis.
Oxygen reacted with
sunlight to produce
ozone gas which
shielded Earth from
lethal short
wavelength radiation
from the Sun and set
the stage for the
appearance of animal
and human life.
Today, humans are
releasing large amounts of
greenhouse gases into the
atmosphere which may be
resulting in global
warming.
This warming is due to the
greenhouse effect.
Astronomy 04
The Solar System Chapter
21.1:
“The Moon”
Please pick up your Test 2 Scantron on front table
if you haven’t already.
The diameter of the Moon is
3476 km (2160 miles) with
a mean distance from the
Earth of 384,000 km (239,
000 miles).
The distance of the Moon from
Earth varies from about …
220,000 to 260,000 miles.
The Moon has a gravity 1/6
that of Earth.
The Moon has no atmosphere.
The combination of the
Moon's lower mass and its
smaller radius means that
its surface gravity is 1/6
the Earth's surface gravity.
Walking on the Moon is
much different from
walking on the Earth, as is
falling on the Moon.
The Moon/Earth mass ratio is
1/80.
The Moon is made mostly of
rock with little metallic
material.
The average density of the
Moon is 3.37 g/cm3 which
is consistent with basaltic
silicates and not consistent
with a large iron (Fe)/nickel
(Ni) core like the Earth.
This relates to the Giant Impact
Theory of the Moon’s
formation.
The lunar surface is a grey-tan color with a low albedo of 0.07
General Properties of the Moon
The Moon has 1/80th mass of Earth and 1/6th the gravity – not
enough gravity to retain an atmosphere.
Any gases expelled or outgassed during the Moon’s early
history have escaped.
Luna 3 was a Russian spacecraft which returned first photos of
Moon’s far side in 1959 and Luna 9 first spacecraft to land on
Moon in 1966.
It was the U.S. Apollo Program which used 9 spacecraft
during the period 1968-72 to put 12 astronauts on the Moon’s
surface.
The U.S. Apollo Program accomplished three major objects
for lunar science:
 It collected 837 lbs of moon rock which was returned to Earth.
 It deployed ALSEP (Apollo Lunar Surface Experiments
Packages)
 The Apollo Command Module which orbited Moon
photographed and analyzed the lunar surface.
Today no nation has the technical ability to return to the
Moon. It would take a ten year committed effort to do so.
Moon’s surface is covered with fine-grained soil or dust
a few cm deep.
The Moon has a cold
solid interior and little
seismic activity.
The Moon is
geologically dead and
has experienced little
change over the last 3.5
billion years.
The Moon also lacks a
magnetic field which
would be generated by
motions in liquid
metallic core.
Moon rock has been
dated from 3.3 to 4.4
billion years. The
oldest earth rock is
dated to 3.8 billion
years.
Chapter 21.1: “The Moon”
Please pick up your Test 2 Scantron on front table
if you haven’t already.
The Major Surface
Features:
•
•
•
•
•
•
•
Maria,
Highlands
Craters
Rays
Impact Basins
Mountains
Rilles (Valleys)
The Moon’s surface
shows light rough cratered
areas and dark relatively
smooth areas with fewer
craters.
The dark areas are called
maria or seas.
Maria
Maria cover 17% of Moon’s surface and are much less cratered.
They consist of volcanic plains and impact basins. They are
composed of basaltic rocks dated to 3.8 billion years.
Maria:
• Dark-colored regions which
turn out to be smooth plains
of basaltic lava.
• They are the remnants of
large impact events that
cracked the crust and
allowed the lava from the
mantle to flow upward and
erase early cratering.
• Note that the impacts must
have occurred after the
initial phase of cratering.
The Moon – Part 2
Highlands:
• The lighter colored,
heavily cratered regions
are called the lunar
highlands.
• The bare, chaotic terrain
indicates that these regions
are primordial and one
would expect the oldest
rocks in these regions.
Lunar Highlands
The lunar highlands are the oldest geologically. They date
to 4.4 billion years and are composed of anorthosites
(silicate rocks). The lunar highlands are heavily cratered.
Normal, round craters are due
to impacts from objects up to
a couple thousand meters.
Object larger (asteroids) will
typically crack the crust and
form impact basins.
Lunar mountains have low rounded profiles and are the result of
early impacts.
Mare Oriental: The Moon’s Largest
The Moon – PartImpact
2
Basin
Geological History of the Moon:
The weight of the evidence is that the Moon was active
geologically in its early history, but the general evidence
suggests that the Moon has been essentially dead geologically
for more than 3 billion years.
Based on that evidence, we believe the chronology of Lunar
geology was as follows:
The Moon was formed about 4.5 billion years. The surface
was subjected continuously to an intense meteor bombardment
associated with debris left over from the formation of the Solar
System.
As the intense meteor bombardment associated with debris left
over from the formation of the Solar System continued, most
of the craters that we now see on the surface of the Moon were
formed.
The largest meteoroids punctured the Moon’s crust and
lava poured out from inside the Moon producing the
Moon’s mare and impact basins.
The regions that were not covered by the lava flows are the
present Highlands; thus, they are heavily cratered, and
formed from different rocks than the seas.
The volcanism stopped about 3.1 billion years ago: the
Moon has been largely dead geologically since then except
for the occasional meteor impact or small moonquake, and
micro-meteorite erosion of the surface.
Erosion is slow on a world without an atmosphere and is
caused by:
1) slumping (gravity)
2) other impacts
3) temperature changes
4) moonquakes
The result is that young craters have sharp edges (usually less
than 200 million years old) and old craters are rounded,
smoother (with ages of order a billion years old).
Current crater-formation-rate can be estimated from the number
of craters and the number of potential projectiles present in the
Solar System today.
It indicates a crater of 1 km is formed every 200,000
years.
A 10 km crater is formed every few million years.
A 100 km crater every billion years.
Both this and radioactive dating of moon indicates age of 4.5
billion years.
Origin of the Moon
The Fission Theory suggests the Moon broke off from
Earth. But this is Impossible physically. It cannot be
modeled by computer. If this were then case then why
are Earth and the Moon such different compositions?
The Capture Theory proposes the Moon formed
elsewhere but was captured by Earth’s gravity. But this
is highly improbable mechanically.
Origin of the Moon
The Sister Theory suggests the Moon formed
together with but independent of Earth.
The Giant Impact Theory suggests the Moon
formed when a giant planetesimal struck Earth and
threw material off into space.