A1 06 Earth

Earth’s Geology
LACC: §7.2, 3, 4

• Understand Earth’s interior: core (inner and
outer), mantle, crust.
• Understand Earth’s geological features
• Understand Earth’s some of the Earth’s
extinction events.
An attempt to answer the “big question”: what is
out there?

Wednesday, March 3, 2010 1

Earth’s Interior

http://earth.unh.edu/esci402/docs/Earth%20Interior.jpg


Earth’s Interior

http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT307/HTML/AT30703.HTM


Earth’s Interior
Seismic waves travel at about 10 km/
sec and, from mapping of the timing and
type of wave around the globe, we are
able to map the interior of the Earth.
Changes in refraction of seismic waves
are due to sharp changes in the density
= discontinuities due to chemical
composition.
The result is that we know that the
interior of the Earth has 4 components:

• a thin crust of density 3.3 gm/cc
composed of metals, silicates (a
substance called basalt)
• a semi-solid mantle of density 3.5 to
5.5 gm/cc composed of olivine Fe
oxides
• a liquid outer core of density 9 to 11
gm/cc composed of molten Fe
• a solid inner core of density 17 gm/cc
composed of Fe and Ni.
http://abyss.uoregon.edu/~js/ast221/lectures/lec13.html


The Earth: Interior Heat
A cross-section of the Earth reveals....
a thin, hard crust ranging from 10 to
100 kilometers thick....
a donut-shaped mantle 2,900 kilometers
thick. Instead of dough, it consists of
viscous molten rock that ﬂows very
slowly, on a geological time scale. "It
moves about as fast as your ﬁngernails
grow," Marone explains....
a two-part core. "The inner part is
about the size of our moon," Marone
says, "and has a density of essentially
steel." The outer core surrounding it is
an ocean of liquid metal 2,300
kilometers thick.

the vast majority of the heat in Earth's interior—up to 90 percent
—is fueled by the decaying of radioactive isotopes like
Potassium 40, Uranium 238, 235, and Thorium 232....
http://www.physorg.com/news62952904.html


The Earth: Tectonic Plates
Earth is the largest terrestrial planet; therefore, it is
taking the longest to cool. It’s crust (Si, O, Fe, Al,
Mg; 3 g/cm3) is broken up into >12 sections
called tectonic plates which are ﬂoating on a
convecting mantle.
The interior is hot due to (accretion,
differentiation, and) radioactive decay.
Signiﬁcant erosion keeps Earth’s surface young--
a few hundred million years old. (The oldest rocks
are 3.9 billion years old. All the planets formed
4.5 billion years ago.)


The Earth: Tectonic Plates
5:17
http://www.youtube.com/watch?v=QDqskltCixA
The Early Earth and Plate Tectonics

http://www.neiu.edu/~llsander/earthquakes.html


Hot Spots
...the Hawaiian Island
and the seamounts
that extend from
Hawaii to the Aleutian
trench show the
movement of the
Paciﬁc plate as it
moved over the hot
spot. Radiometric
dating shows that the
volcanic activity
decreases in age
toward the island of
Hawaii, which is now
over the hot spot.

http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html


The Earth: Impact Craters

Current total
number of
conﬁrmed impact
structures: 176

http://www.unb.ca/passc/ImpactDatabase/CINameSort2.htm


The Earth: Arizona Impact

Photograph by David Roddy, United States Geological Survey.
http://www.lpi.usra.edu/science/kiefer/Education/SSRG2-Craters/craterstructure.html



Meteor Crater in Arizona is one of the best
known examples of an impact crater on Earth.
The crater is 1.2 kilometers (0.74 miles) in
diameter and 200 meters deep. It formed
approximately 49,000 years ago when an iron
meteorite that was roughly the size of a school
bus struck the Arizona desert east of what is
now Flagstaff.

http://www.lpi.usra.edu/science/kiefer/Education/SSRG2-Craters/craterstructure.html


In a blinding ﬂash, a huge iron-nickel meteorite
or dense cluster of meteorites, estimated to have
been about 150 feet across and weighing several
hundred thousand tons, struck the rocky plain
with an explosive force greater than twenty
million tons of TNT (or around 1000 Hiroshima
bombs). Traveling at supersonic speed, this
impact generated immensely powerful shock
waves in the meteorite, the rock and the
surrounding atmosphere. In the air, shock waves
swept across the level plain devastating all in the
meteor's path for a radius of several miles.
http://www.meteorcrater.com/eventsfun/exptheimp.htm


Tunguska Blast

Trees near the Podkamennaya Tunguska River in Siberia still looked
devastated nearly two decades after a large meteorite exploded
above the ground in June 1908. The Tunguska event, which ranks as
one of the most violent cosmic impacts of this century, leveled nearly
800 square miles of forested taiga.
Smithsonian Institution
http://www.skyandtelescope.com/community/skyblog/newsblog/12662606.html


The Earth: Chicxulub
http://www.youtube.com/watch?v=5qJPTjMnwNk 2:25
Chicxulub impact visualization

The Chicxulub Crater is believed
to be the result of the collision with
an asteroid measuring some 10 to 20
km across. The environmental effects
that accompanied its formation were
thought to have been responsible for
the mass extinction at the end of
the Cretaceous period, about
65 million years ago, in which
the last of the dinosaurs, along with
many other species, disappeared (see
Cretaceous-Tertiary Boundary).
http://www.daviddarling.info/encyclopedia/C/Chicx.html


Ice Ages
Milankovich cycles are cycles in
the Earth's orbit that inﬂuence the
amount of solar radiation striking
different parts of the Earth at different
times of year. They are named after a
Serbian mathematician, Milutin
Milankovitch, who explained how
these orbital cycles cause the advance
and retreat of the polar ice caps.
Although they are named after
Milankovitch, he was not the ﬁrst to
link orbital cycles to climate.
Adhemar (1842) and Croll (1875)
were two of the earliest.
http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html


Ice Ages

http://universe-review.ca/I09-15-iceages.jpg


Earth: Life?

http://www.answers.com/topic/extinction-intensity-png-1


Earth’s Geology
LACC: §7.2, 3, 4
• Understand Earth’s interior: core (iron; solid
inner, liquid outer), mantle (rocky), crust;
differentiation
• Understand Earth’s geological features: a few
hundred million years old; plate tectonics and
erosion (and a few hundred impact craters)
• Understand Earth’s some of the Earth’s
extinction events: impacts (e.g. Chicxulub),
Milankovich cycles
An attempt to answer the “big question”: what is
out there?

LACC HW: Franknoi, Morrison, and Wolff,
Voyages Through the Universe, 3rd ed.

• Ch. 7, pp. 171-172: #1.

Due at the beginning of next class period.
Be thinking about the Solar System Project.


Earth’s Atmosphere
LACC §7.2, 3, 4

• Earth’s Atmosphere: composition, pressure,
and temperature
• The Evolution of Earth’s Atmosphere
• Life on Earth
An attempt to answer the “big question”: where
did we come from?


The Earth: The Atmosphere
• The greenhouse effect on Earth
heats our planet by about 55°F.
• The Earth’s atmosphere (and
magnetosphere) protect us from
dangerous radiation and meteors.
• Earth’s surface temperature and
pressure allow for liquid water on
its surface!


The Earth: The Atmosphere
Composition 1 bar surface
pressure
• N2 77%
• O2 21%
59°F average
• Ar 1%
surface
• H2O varies temperature
• CO2 varies


Earth: Black Body
Temperature

....Earth ...
255 K (-18 °C or
-0.5 °F). ...this
would be the
temperature of
the planet if it had
no atmosphere.

http://www.ldeo.columbia.edu/~kushnir/MPA-ENVP/Climate/lectures/energy/Radiative_Heat_Transfer.html


Earth: The Greenhouse Effect

http://maps.grida.no/go/graphic/greenhouse-effect



[The] graphic [on the previous slide] explains how
solar energy is absorbed by the earth's surface,
causing the earth to warm and to emit infrared
radiation. The greenhouse gases then trap the
infrared radiation, thus warming the atmosphere.

http://maps.grida.no/go/graphic/greenhouse-effect


The main greenhouse gases

Greenhouse gases Chemical Pre-industrial Concentration Atmospheric Anthropogenic Global warming
formula concentration in 1994 lifetime (years)*** sources potential (GWP) *

Fossil fuel combustion
Carbon-dioxide CO2 280 ppmv 358 ppmv 50-200 Land use conversion 1
Cement production

Fossil fuels
Rice paddies
Methane CH4 700 ppbv 1720 ppmv 12-17 Waste dumps
21 **
Livestock

Fertilizer
Nitrous oxide N 2O 275 ppbv 312 ppmv 120-150 industrial processes 310
combustion

Liquid coolants.
CFCs CFC12 0 503 pptv 102
Foams
125-152

HCFCs HCFC-22 0 105 pptv 13 Liquid coolants 125

Production
Perfluorocarbon CF4 0 110 pptv 50 000 of aluminium
6 500

Production
Sulphur hexa-fluoride SF6 0 72 pptv 1 000 of magnesium 23 900

Note : pptv= 1 part per trillion by volume; ppbv= 1 part per billion by volume, ppmv= 1 part per million by volume

* GWP for 100 year time horizon. ** Includes indirect effects of tropospheric ozone production and stratospheric water vapour production. *** On page 15 of the IPCC SAR. No
single lifetime for CO2 can be defined because of the different rates of uptake by different sink processes.
GR I D
Arendal UNEP water?
Source: IPCC radiative forcing report ; Climate change 1995, The science of climate change, contribution of working groupe 1 to the second assessment report of the
intergovernmental panel on climate change, UNEP and WMO, Cambridge press university, 1996.

http://maps.grida.no/go/graphic/main-greenhouse-gases


Earth: Atmospheric Evolution

http://www.fas.org/irp/imint/docs/rst/Sect19/Sect19_2a.html



Materials for the atmosphere
were brought to the earth by
comets accreted during its
formation, then released by
volcanoes (From Don Dixon
http://cosmographica.com/gallery/
index.html). Additional late-
arriving comets would have added
additional material to the oceans
and atmosphere.

http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/earth.htm


Origin of the Earth's Atmosphere
After losing most of its original H and He, the
Primordial Atmosphere of the Earth was built up by
outgassing of the crust by volcanos:

•

Mostly H2O and CO2

•

Small amounts of N2 and sulfates

•

No oxygen (O2).

This is very different than our present atmosphere.
How did our atmosphere get the way it did?
http://ftp.astronomy.ohio-state.edu/~pogge/Ast161/Unit5/atmos.html



http://www.globalchange.umich.edu/gctext/Inquiries/Inquiries_by_Unit/Unit_8.htm



http://www.physast.uga.edu/~jss/1010/ch10/ovhd.html


Where did all the CO2 go?
The primordial atmosphere had ~1000 times more
CO2 than it does now. Where did it all go?

•

H2O condensed to form the oceans.

•

CO2 dissolved into the oceans and
precipitated out as carbonates (e.g., limestone).
Most of the present-day CO2 is locked up in crustal
rocks and dissolved in the oceans.
By contrast, N2 is chemically inactive

•

It stayed a gas in the atmosphere and become
its dominant constituent.


Where did the O2 come from?
The second major constituent of the present-day atmosphere is
Oxygen (O2), but it was absent in the Primordial Atmosphere. Where
did all the O2 come from?
• Molecular Oxygen (O2) comes primarily from photosynthesis
in plants and algae.
• The O2 content of the atmosphere has increased from 1% to 21%
during the past 600 Myr.
Ozone (O3):
• Forms in stratosphere from O2 interacting with solar UV
photons.
• Blocks UV photons from reaching the ground.
This made land life possible as solar UV radiation is hazardous to life.
The presence of O2 and O3 in our atmosphere is a sign of life
(photosynthesis).


Earth: Life?
• 3.9 billion years ago: chemical evidence of
life
• 3.5 billion years ago: Stromatolite colonies
• 2 billion years ago: O2 accumulate is the
atmosphere
• 65 million years ago: Chicxulub impact
results in extinction of dinosaurs
• 200 thousand years ago: modern humans
• 1 hundred years ago: radio broadcasts

Earth: Life?
Colonies of trillions of these bacteria built up cabbage-like
structures called stromatolites. The bulk of a
stromatolite colony consists of layers of calcium
carbonate interspersed with mattes deposited by the
cyanobacteria (which are photosynthetic). Stromatolites
still exist on Earth but are rare (mainly at two localities in
Australia).

http://www.fas.org/irp/imint/docs/rst/Sect19/Sect19_2a.html


Earth: Climate Change

http://www.global-greenhouse-warming.com/ice-ages-and-sea-levels.html


The Medieval Warm Period was a time of warm climate in Europe, the height
of which was from about 950 until 1100 A.D. The warm climate overlaps with a
time of high solar activity called the Medieval Maximum. The Medieval Warm
Period occurred before the Little Ice Age (1350-1850 A.D.), a time of
particularly cool climate in Europe and other places around the world.
The graph on the left, a
reconstruction of average global
temperatures over the past 1000
years, shows that during the
Medieval Warm Period the
temperatures were likely similar to
the ﬁrst part of the 20th century,
climate cooled during the Little Ice
Age, and has warmed dramatically
in recent decades. Temperatures
during the Medieval Warm Period
were likely cooler than the
temperature has been for the past
few decades.
http://www.windows.ucar.edu/tour/link=/earth/climate/medieval_warm_period.html&edu=high


All ﬁve global
temperature
estimates
presently show
stagnation, at least
since 2002. There
has been no
increase in global
air temperature
since 1998, which
was affected by
the oceanographic El Niño event. This does not exclude the possibility that
global temperatures will begin to increase again later. On the other hand, it
also remain a possibility that Earth just now is passing a temperature peak, and
that global temperatures will begin to decrease within the coming 5-10 years.
Only time will show which of these possibilities is the correct.
http://www.climate4you.com/GlobalTemperatures.htm#Comparing
%20global%20temperature%20estimates


Earth’s Atmosphere
LACC §7.2, 3, 4
• Earth’s Atmosphere: composition (N2, O2),
pressure (1 bar), and temperature (59 °F), the
greenhouse effect
• The Evolution of Earth’s Atmosphere: volcanic
outgassing, comet impacts, thermal escape.
• Life on Earth: earliest fossils, O2 levels, climate
change
An attempt to answer the “big question”: where
did we come from?


LACC HW: Franknoi, Morrison, and Wolff,
Voyages Through the Universe, 3rd ed.

• Ch. 7, pp. 171-172: #5.

• Ch 8: Tutorial Quizzes accessible from:
www.brookscole.com/cgi-brookscole/course_products_bc.pl?
http://

ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19

Due at the beginning of the next class period.
Be thinking about the Solar System Project.


A1 06 Earth

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