Transcript Ch. 30.1 The Earth`s Moon

Ch. 30.1 The Earth’s
Moon
 Satellite—a
body that orbits a larger
body.
 The moon is earth’s natural satellite.
 The moon has weaker gravity (1/6th
that of earth) because it has less
mass than earth.
 Moon’s gravity too weak to hold
gasses, so no atmosphere.
 Moon’s
temp. ranges from 134 C
during the day to -170 C at night.
 Moon rotates once every 27.3 days,
but a lunar day is 29.5 earth days
because the moon is also travelling
around the sun at the same time.
The Lunar Surface
 Observers
from earth see light and
dark patches.
 Light areas are called highlands, and
consist of light-colored rock.
 Dark areas are called maria (latin for
seas) and are smooth and reflect
little light. Made of dark solidified
lava, from ancient volcanic eruptions.
 Rilles
are long deep channels that
run through the maria. Probably
lava channels.
Craters
 Cover
moon’s surface. Most formed
about 4 billion years ago.
 Object striking moon leaves bowlshaped depression. Displaced
material settles out in streaks, called
rays.
 Since no erosion on the moon, its
surface has changed little since it
formed.
Lunar Rocks
 Much
of moon’s surface crushed into
dust and fragments by meteorite
impacts.
 Regolith—the layer of dust and
fragments (1 m to 6 m) that covers
the lunar surface.
 Surface lunar rocks composed mainly
of oxygen and silicon.
 Highland
rocks are light-colored,
course-grained anorthosites, rich in
calcium and aluminum.
 Maria rocks are fine-grained, dark
colored basalts, high in titanium,
iron, and magnesium.
 Breccia—fragments of other rocks
melted together after meteorite
impacts. Common all over.
The Interior of the Moon
 Info
from seismographs placed by
Apollo astronauts.
 Weak moonquakes recorded.
 Crust is 60 to 100 km thick.
 Underneath is denser mantle, to a
depth of about 1000 km.
 Possibly slightly molten or small iron
core. Almost no magnetic field.
Development of the Moon
 Giant-impact
hypothesis– Mars-sized
object struck the earth and ejected
fragments into orbit, which
eventually joined to form the moon.
 2nd Stage—surface of moon covered
by ocean of molten rock. Denser
parts separated and sank to the
core.
 3rd
Stage—surface cooled to form
crust. Meteorites struck and broke
through, causing molten rock to flow
up and form the smooth maria.
 About 3 billion years ago, impact
activity decreased, and geologic
activity stopped due to cooling.
Rayed craters formed by most recent
impacts.