Download Origin of the Atmosphere.pps

(Pflueger )
Today’s Objectives
Students will be able to:
1. Discuss how we have arrived
at the current atmosphere
from the original atmosphere.
2. Compare and Contrast the
(3) major atmospheres and
their compositions.
Origin of the Atmosphere
• Has our our atmosphere always
been like it is today?
The correct answer is NO!
…and here is some evidence
why scientist think this.
4.6 Billion Years Ago
• The earliest atmosphere is
believed to have been mainly…
Hydrogen and Helium
• These were the 2 most
abundant gases found in the
early universe.
• Methane and Ammonia were
also found at high levels.
Where did it go?
• It’s believed that this early
atmosphere escaped into space.
Why might this be the case?
1.Early Earth gravity too weak.
2.Earth without differentiated core,
thus no magnetic field to deflect
solar winds.
3.Heat of Earth and solar system.
As Things Got Older
• Eventually a second, more
dense, atmosphere formed.
• Gradually surrounded the
Earth as gases escaped into
the atmosphere from
volcanoes and steam vents.
*This is assuming that volcanoes spewed
out the same gases as they do today.*
Atmosphere Part II
Gases used from volcanism
• 80% water vapor (H2O)
• 10% carbon dioxide (CO2)
• 4-6 % nitrogen (N2)
This continued on for millions of years!
Making of a Wet Day
• Millions of
years of
constant
“outgassing”
provides a rich
supply of
water vapor.
• During Achaean
(DOMC - Haifi)
What Happened to the CO2
•
Large amounts of CO2 were
dissolved into the oceans.
•
Through chemical and early
biological processes, the
CO2 became locked up in
carbonate sedimentary
rocks, such as Limestone.
How Did We Get N2?
1.Much of the water vapor
condensed, either as clouds,
rain, or ground water.
2.The concentration of CO2
was quickly dwindling.
3.Nitrogen gradually built up.
This is due to it being chemically inactive.
Then O2 Made it Big
• Believed oxygen concentrated
extremely slowly as:
1. Photochemical
Dissociation:
splitting of H2O by UV-rays.
*The lighter hydrogen probably rose and
escaped into space.*
• If O2 levels 1-2% of current,
would be enough to form O3
Now We Have Life
2. Enough
oxygen accumulated
for primitive plants to evolve,
around 2-3 billion years ago.
• With an increase in plant life,
using photosynthesis, the
atmosphere was greatly
enriched with oxygen.
Evidence of an Early Atmosphere
1. Precipitation of limestone
in great quantities.
2. The oxidation of iron to
form banded deposits in early
rocks.
3. The distribution of various
minerals in most early
sedimentary rocks.
Evidence of an Early Atmosphere
Limestone
(Stone Museum)
Banded-iron
(Stone Museum)
Composition Today
• After 2-3 Billion years, the
composition is much different
today.
• There is more oxygen (that is a
good thing) and a lot less carbon
dioxide (also a good thing)
Lets compare today with yester-year.
Composition Comparison
Today
Yester-Year
78 %
Nitrogen
4-6%
21%
Oxygen
< 1%
0.9%
Argon
0-1%
Carbon dioxide
10%
Water Vapor
80%
Ozone
0%
0.033%
0-4%
0-.000007%
< 1%
Other gases
3-4%
Assignment For Thursday
(Stimac)
Works Cited
Department of Maritime Civilizations - University of Haifa. “Earth Origins and
Formation.” 10 Apr 2006.
<http://maritime.haifa.ac.il/departm/lessons/ocean/lect03.htm>.
Pflueger, Nathan. “The Origins of the Atmosphere.” 14 Oct 2003. 11 Apr 2006.
<http://eugevir.tripod.com/origins/atmosphere.html>.
Stimac, John. “The Atmosphere – origin and structure.” 11 Apr 2006.
<http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html>.
Stone Museum. “Types of Rock.” 10 Apr 2006. <http://www.geol.sci.hiroshimau.ac.jp/~geotect/stonemuseum/Classification-j.html>.