Chapter 7 earth and the terrestrial world
Mercury: craters smooth plains cliffs
Venus: volcanoes few craters radar view of a twin peaked
volcano
Mars: some craters volcanoes riverbeds
Moon: craters smooth plains
Earth: volcanoes craters mountains river beds
*****Earth as a planet*****
Why is earth geologically active?
Earths interior
Core: highest density nickel and iron
Differentiation
Gravity pulls high density material to center
Lower density material rises to surface
Material ends up separated by density
Lithosphere
A planets outer layer of cool rigid rock is called the
lithosphere
It floats on the warmer softer rock that lies beneath
Strength of rock
Rock stretches when pulled slowly but breaks when pulled
rapidly
The gravity of a large world pulls slowly on its rocky
content shaping the world into a sphere
Heat drives geological activity
Convection hot rock rises cool rock falls
One convection cycle takes 100 million years on earth
Source of internal heat
1 gravitational potential energy of accretions planetesimal
2 differentiation
3 radioactivity
Heating of interior over time
Accretion and differentiation when planets were young
Radioactive decay is most important heat source today
Cooling of interior
Convention transports heat as hot material rises and cool
material falls
Conduction transfer heat from hot material to cool material
Radiation sends energy to space
Role of size
Smaller worlds cool faster and harden earlier
The moon and mercury are now geologically dead
Surface area o volume ratio
Heat content depends on volume
Loss of heat through radiation depends on surface area
Time to cool depends on surface area divided by volume
Large objects have a smaller ratio and cool more slowly
Planetary magnetic fields
Moving charges particles create magnetic fields
A planets interior can create magnetic fields if its core is
electrically conducting connecting and rotating
Earth magnetosphere
Earth magnetic field protects us from charges particles from
the sun
The charged particles can create aurorae northern lights
How do we know what inside a planet
P waves go through earth core but S waves do not
We conclude that earths core must have a liquid outer layer
What processes shape earths surface
Geological processes
Impact cratering impacts by asteroids or comets
Volcanism eruption of molten rock onto surface
Tectonics disruption of a planets surface by internal stress
Impact cratering
Most crating happened soon after the solar system formed
Craters are about 10 times wider than the objects that made
them
Small craters greatly outnumber large ones
Volcanism
Volcanism happens when molten rock magma finds a path
through lithosphere to the surface
Molten rock is called lava after reaches the surface
Out gassing
Volcanism also releases gases from earths interior into the
atmosphere
Tectonics
Convention of he mantle creates stresses in the crust called
tectonic forces
Compression forces make mountains ranges
A valley can form where the crust pulls apart
Erosion
Erosion is a blanket term for weather driven processes that
break down or transport rock processes that cause erosion include
glaciers rivers wind
How does earth atmosphere affect the planets?
Radiation protection
All X-ray light is absorbed very high in atmosphere
Ultraviolet light is absorbed by ozone
Greenhouse gas
Any gas that absorbs infrared
Greenhouse gas molecules with two different types of elements
Not a greenhouse gas
Earth is much warmer than Venus
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