Fig. 17-1, p. 394

1
Fig. 17-1, p. 394
2
http//www.rockhounds.com/grand_hikes/geology/over
view.shtml
3
Fig. 18-1, p. 418
4
Atmospheric Development

• Primordial Atmosphere of Earth
• Hydrogen and Helium
• Ammonia and methane
• Thought to have escaped into space from Earths
  hot surface.
• Second, dense atmosphere developed
• Mostly water vapor (80), carbon dioxide (10),
  nitrogen (5 )
• Source volcanic activity and steam vents also
  extraterrestrial impacts (comets)

5
Atmospheric Development

• Atmospheric Transformation
• Water vapor evaporated, condensed into clouds and
  extensive, long-lived rain fell for thousands of
  yearswater vapor decreased
• Carbon dioxide dissolved into the newly-formed
  oceans and was locked up into carbonate
  (limestone) rocksCaCO3carbon dioxide decreased
• Nitrogen was then enriched by the relative
  decreases of water vapor and carbon dioxide.

6
Atmospheric Development

• No free oxygen
• Photodissociation--Sunlight is thought to have
  split water vapor into hydrogen and oxygen,
  hydrogen escaped, oxygen left behind (2-3 by ago)
• Algal stromatolites enriched the atmosphere in
  oxygen, which also allowed for the formation of
  ozone (O3).
• Ozone prevented most of the UV rays from the Sun
  reaching the Earths surface by absorbing the
  rays.
• O2 levels rose from 1-10 during the Proterozoic
  Eon.
• Present levels of O2 were probably not achieved
  until 400 Ma.
• but it was actually the steady evolution of
  unicellular organisms that produced oxygen and
  brought about the change in the atmosphere's
  makeup.
• How Weather Works
• by Robert Lamb http//science.howstuffworks.com/
  weather1.htm
• http//www.ux1.eiu.edu/cfjps/1400/atmos_origin.ht
  ml

7
Geologic Principles

• Principle of Uniformitarianism (the geological
  processes observed today are the same as in the
  past and in the future).
• Principle of Superposition (each sedimentary
  layer in a tectonically undisturbed sequence is
  younger than the one beneath it and older than
  the one above it)
• Principle of Original Horizontality (sediments
  are deposited as essentially horizontal beds)

8
Alternating beds of limestone and shale
Fig. 7-10a, p. 156
9
Uniformitarianism

• The present is the key to the past.
• Attributed to Scottish geologist James Hutton
  (1726-1797)
• Great geologist, lousy writer
• Principle of uniformitarianism The present-day
  processes have operated throughout geologic time
  and will be the same processes to operate in the
  future.
• Charles Lyell (1830) wrote Principles of Geology
  and more eloquently wrote about uniformitarianism.

10
Uniformitarianism

• Given enough time
• A stream could carve a valley

11
(No Transcript)
12
(No Transcript)
13
Uniformitarianism

• Given enough time
• Ice could erode rock

14
Fig. 1-8, p. 12
15
Fig. 1-19a, p. 22
16
Fig. 1-19b, p. 22
17
Uniformitarianism

• Given enough time
• Wind can sculpt rock

18
(No Transcript)
19
Uniformitarianism

• Given enough time
• Weathering could take down a mountain.
• A little at a time for a long time can have a
  huge effect.

20
Geologic Time
21
Geologic Time

• Earth is 4.6 billion years old (as old as the
  formation of the solar system)
• To a geologist, recent geologic events are those
  that occurred within the last million years.
• The Earth goes through cycles that are much
  longer in duration than our human perspective of
  time.

22
Assessing the Age of the Earth

• Geologists placed relative dates on exposed rock
  formations based on
• similarities and differences in rock composition
  and the preserved biota.
• relative positions of these rock formations
• Geologists later placed an absolute dates on rock
  using radiometric dating techniques to confirm
  relative ages.

23
Fig. 1-18, p. 21
24
Geologic Time Scale
Ages in millions of years
Todays Geologic Date Recent Epoch Quaternary
Period Cenozoic Era Phanerozoic Eon
The Earth is currently experiencing an
interglacial episode
Fig. 17-1, p. 394