Earth

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Earth

• A Terrestrial Planet

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Atmosphere of the Earth
Composition
Nitrogen (N2) 78 Oxygen (O2) 21 Argon
(Ar) 0.9 Carbon Dioxide (CO2) 0.03 Water
Vapor (H2O) 0.1 3
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Greenhouse gases are gases that
absorb strongly in the ultraviolet part of the
spectrum
absorb strongly in the visible part of the
spectrum
absorb strongly in the thermal infrared
destroy ozone

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The Origin of the Earths Atmosphere
When the Earth was formed, because of the
high temperatures in the inner protoplanetary
disk, it had essentially no atmosphere. The
Earths atmosphere came from two sources
1) Volcanic outgassing
2) Collisions with comets and asteroids
The original atmosphere of the major terrestrial
planets (Venus, Earth Mars) consisted mainly of
CO2 and water vapor
All three major terrestrial planets probably had
planet- wide oceans originally.
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We will examine the evolution of the atmospheres
of the three major terrestrial planets later.
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The nature of the interior of the Earth can be
deduced from the behavior of P and S waves
from earthquakes.
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Magnetic Field
Among the Terrestrial planets, the Earth has the
strongest magnetic field.
The magnetic field of the Earth is generated in
the interior via the Dynamo Mechanism.
For this mechanism to work, two properties must
be present 1) the planet must possess a liquid,
electrically conductive core and 2) the planet
must be a rapid rotator.
Both of these conditions are fulfilled for the
Earth.
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Venus has a liquid conductive core like the
Earth. Its rotational period is 243 days. Which
statement do you think is true?
Venus magnetic field is much stronger than the
earths
Its magnetic field is about the same strength
as the earth
Its magnetic field is much weaker than the earth


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Earths Magnetosphere
Solar Wind
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Aurora Borealis
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The Age of the Earth
According to the Nebular theory, the Earth was
formed at the same time as the Sun and the other
planets. The age of the Earth, and thus the
solar system can be estimated from radioactively
dating the geologically oldest rocks on Earth
and other solar system bodies.
Uranium-235 is a naturally occurring radioactive
isotope of Uranium. It decays to Lead-207 with a
half-life of 0.7 billion years.
?The relative abundances of 235U and 207Pb
are correlated with the age of the rock.
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Potassium Argon dating is also used 40K ? 40Ar
with a half-life of 1.3 billion years
The oldest rocks on the Earth are dated to 3.7
3.8 billion years ago. The oldest dated
minerals are dated to 4.0 4.2 billion years
ago. These dates are lower limits to the actual
age of the Earth. The oldest Moon rocks date
back to 4.4 4.5 billion years ago, and the
oldest meteorites to 4.5 4.6 billion years.
Thus we believe the age of the Earth is 4.5 4.6
billion years.
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Why are the oldest rocks on Earth younger than
the oldest rocks in the solar system?
because Earth was formed late in the
solar-system formation process
because Earth was captured by the sun after the
formation of the solar system.
because of geological activity on the Earth


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Earth Geology
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Earth is a geologically active planet. The
unifying feature of Earth geology is Continental
Drift.
The Earths crust is divided into a number of
continental plates which can drift relative to
each other and collide with each other.
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Earthquake zones on Earth coincide either with
crustal boundaries, or where new crust is being
formed.
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Continental drift is driven by sea-floor
spreading
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Sea-floor spreading is driven by deep convection
currents in the Earths semi-molten mantle.
Rift
Trench
Mountains
Convection currents
Subduction Zone
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Currently, the Atlantic ocean is widening due to
sea-floor spreading. 250 million years ago, the
African plate was in contact with the North and
South American plates.
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The collision of the African plate with the N.
American plate about 250 300 million years ago
led to the formation of the Appalachian
Mountains.
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Both the Appalachian Mountains and the
Himalayans were formed from crustal collisions,
although the Himalayans are much more recent.
Why are the Himalayans so much taller than the
Appalachians?

the collision in the case of the Appalachians
was much less forceful
The Appalachian mountains were originally
nearly as tall as the Himalayans, but have worn
down through erosion
Once the Indian plate stops its northward
movement, the Himalayan mountains will subside to
elevations closer to 10,000 feet.

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Evidence for Continental Drift is extensive
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Tides
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Tidal Bulge leads to the slowing of the rotation
of the Earth.