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Earth
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Earth
3rd
place from the Sun
Only known body in solar system with
plate
tectonics
Liquid
water
at surface
Biosphere
Earth is similar in
size
and
diameter
to Venus
Earth's temperature is
moderated
, which is why it is habitable
Internal Structure of the Earth
3 main layers:
Crust
,
Mantle
,
Core
Seismic
waves
are reflected and refracted as they pass through the Earth
Velocity of waves depends on
modulus
and
density
Used to map changes in density with
depth
Mantle Transition Zone
Marked by a
seismic
velocity
discontinuity
Olivine undergoes phase transitions between 440 - 660 km
At 660 km, olivine transforms to
perovskite
Seismic Shadows Zones
Discovery of the Core(s)
Earth's core acts like a
prism
, causing S-wave shadows
Richard Oldham
discovered the outer core in 1906
Harold Jeffreys
found S waves do not pass through the outer core in 1926
Inge Lehmann
recognized waves reflected from a boundary deep within the Earth, outside of the inner core, in 1936
Oceans
Cover
71
percent of Earth
Average depth ~
4.2km
Mariana trench ~
11km
deep
Pressure increases 1 bar every
10
m depth
Average temperature ~
2
celsius
Only ~
5
% of ocean floors explored
We know more about the
topography
of Mars
~
50
-
80
% of all life resides in the oceans
Earth's Atmosphere
Nitrogen
(78%),
oxygen
(21%) and
argon
(1%)
Trace amounts of other gases
4 main layers:
Troposphere
,
Stratosphere
,
Mesosphere
,
Thermosphere
Ionosphere
is extension to space
Contains ~
80
% of atmosphere
Rapidly thins upward
Milankovitch
(
Orbital
)
Cycles
The shape of Earth's orbit (
eccentricity
, 100,000 year cycles)
The angle Earth's axis is tilted with respect to Earth's orbital plane (
obliquity
, 41,000 year cycles from 22.1 to 24.5 degrees)
The direction Earth's axis of rotation is pointed (
precession
, 26,000 year cycle that wobbles like a spinning top)
These control when we get
ice
buildup
at high altitude and hence periods of glaciation and interglacial