AST101H1 Lecture Notes - Lecture 14: Lithosphere, Cn Tower, Bowling Ball

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how do craters form?
Mercury or moon – surface that hasn't been melted or eroded – craters overlap one another
for earth we don't see them, we only see the recent (unclear) ones
earth orbits the sun at 30 km every second
escape speed of earth 11 km
if an object makes its way through the atmosphere – fast enough to vaporize rock (in earth
most of the objects will be vaporized)
shock waves of craters
raised central region – big object that comes in = shock waves through the rocks
shock waves can bounce off other layers of other rocks causing the central regions to
bounce up
click quiz
dropping a bowling ball into a sandbox from the top of the CN tower and it leaves a
Q: is this depression the same as a crater on mercury or the moon?
A: no
explanation: difference in distance from the object being dropped, it will not vaporize
shaping planet surfaces
what can erase craters
tectonics – surface of earth is moving = continental plates are moving (the ground they are
on is subducted and melted)
volcanoes – earths core still hot = layers over the surface of earth with magma/lava
grinds stuff down (mountains)
plate tectonics
earth and venus – active geology (heat coming out of earth, convective motion in the
mantle – tectonic plates – causing seduction zones = crust is melting releasing lava
tectonic plates are driving volcanoes
clicker quiz
Q: icy moon of saturn (enceladus) - which part of its surface is youngest?
option A: craters
option B: smooth surface
answer: B – impacts have been happening for the last billion years for A (craters) and
something erased surface B (water)
clicker quiz
Q: if humans do not try to stop incoming asteroids, what are the odds you will be killed by
an impact?
A: 1 in a million
interiors of terrestrial planets
inactive geology - thicker lithosphere
main difference – heat
3 ways they heat up and 3 ways they lose their heat (cool off)
heating sources (3) – all are strongest when planet is young (after a while the rate of
impacts slow down)
(1) accretion - things smashing into the planet (focuses on outer surface)
(2) differentiation – differentiates by more dense and less dense stuff (by gravity)
(3) radioactivity – some of those atoms decay – releasing energy becomes heat –
comes from exploding stars (stars that died before the sun was born)
(4) tidal heat (heating from the moon)
cooling effect (3)
(1) convection – moving interior around in the motion of rocks, water is less dense
when it heats up therefore it rises
(2) conduction – heat is the motion of the particles therefore their motion can move
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