Earth's surface has changed in its long history and continues to change via the same processes

1. EARTH HISTORY 1:
Geological Changes
ppt. by Robin D. Seamon
HOOK VIDEO: Ian Stewart:
Volcanoes (50 min)

2. • Earth is dynamic (changing)
• Heat from the center
• Energy from the Sun
INSIDE:
• Decay of radioactive isotopes
• The release of this heat causes:
• churning of the molten rock inside
• Release of heat through cracks/vents in the crust
• Convection causes plates of crust to move about

3. OUTSIDE:
• Sun’s Energy on the atmosphere and water make:
• Wind
• Currents
• Evaporation- Water Cycle
• This causes weather &
larger patterns of climate
• It influences Water Cycle
which controls
weathering, erosion, &
deposition
http://www2.mps.mpg.de/projects/sun-climate/se_body.html

4. INSIDE
• 99% of rock inside the Earth is greater than 2,000˚F
(radioactive decay generates the heat)
• Crust: (0.2 – 1.1 % crust
or 4-43 miles deep)
700˚F- 1,500˚F
• Mantle: (45 % interior)
hot magma 7,000˚F
• Core: (54% of interior)
Fe, Ni 10,000˚F

5. COMPOSITION:
• Scientists study earthquake waves
to determine what’s inside
• Pattern of waves through the Earth
shows something dense in the
center
• Fe (iron) fits this description
& also explains magnetic field
http://www.indiana.edu/~geol105/images/gaia
_chapter_3/seismic.htm

7. • Geothermal: relating to
heat inside the earth
DEEPEST man-made hole:
• Kola Superdeep
borehole- NW Russia
• 40,000 ft & then too
hot to dig more
Crust 21 miles deep in
Baltic Region
At 7.4 miles,
300˚F
Average oil
well is ~ 1
mile
Scientists try to harness this geothermal Energy
for renewable Energy source

8. OUTSIDE
• Plate Tectonics: plates move about ½” to 3” a year
• Theory that the Earth’s lithosphere is composed of 10+ plates
that fit together like a puzzle
http://www.bucknell.edu/x17758.xml

9. Spain
http://www.windows2universe.org/earth/images/earth_plates
_usgs_L_2_jpg_image.html

10. http://www.platetectonics.com/oceanfl
oors/index.asp

11. • The plates move slowly on the upper mantle (asthenosphere)
http://kids.britannica.com/comptons/art-156130/A-diagram-shows-the-relationship-
between-volcanic-activity-and-Earths
VIDEO: Plate Tectonics (1.5 min)

12. • Movement is caused by convection inside the Earth
• Hot goes up, cold goes down-
• plates are along for the ride
• Continental Drift: in the 1900’s scientists realized the plates
were moving, but didn’t know why (Alfred Wegner)
1. *VIDEO: The Early Earth & plate tectonics-National Geo (5min)
2. VIDEO: Plate Tectonics: A documentary (7 min)

13. FAULTS LAB

14. Spain
FAULTS LAB

15. Landforms & Forces that Made Them
Constructive or Destructive?
Constructive force: forces that build up new crust
Destructive Forces: forces that destroy crust
Sporadic or Gradual?
Sporadic event: event happened quickly and suddenly
Gradual event: event happened over a long period of time

16. • Volcanoes: sometimes the heat can escape through vents at
the surface; magma & hot gases from inside are released until
pressure is abated
• Largest- Mauna Loa, Hawaii 18,000square miles
• Big eruptions occur several times/Century
• Shield volcano: layers of lava
released from non-explosive
eruptions
(Mauna Kea, Hawaii)

17. • Cinder cone volcano:
pyroclastic material- dust & ash
explodes out (Paracutin, Mexico)
Composite volcano: pyroclastic
explosions followed by slower,
longer flowing-lava (Mt. St. Helens

18. • Earthquakes: tension builds up at plate boundaries until the
plates slip & tension is released- we feel earthquakes
Tsunami: when earthquake happens
under the ocean

19. EVIDENCE in CRUST
• Uplift: places on the crust that bulge upwards because of
pressure underneath
• can help predict future earthquakes or eruptions
http://www.panoramio.com/photo/15735758
http://bc.outcrop.org/GEOL_B10/lecture18.html

20. • Predicts tension at
a divergent
boundary
• Predicts loss of
material below
• Subsidence: places on the crust that are sinking down in
elevation

21. • Rebound: places on the crust that rise in elevation when a
heavy weight is removed
• Ice sheet melts
• During droughts when water table is emptied
• Heavy building is removed
http://bprc.osu.edu/education/rr/webex/WebExGridLinks2Pg6.html

22. FAULTS & BOUNDARIES
• Compression: two plates are pushed together at convergent
boundaries
Results in:
• Subduction (cooler oceanic crust goes beneath
warmer continental crust)
• Folding (crust folds into mountains)
• Faulting (crust pushes up or falls in block mountains)
• Hanging wall
• Footwall
• earthquakes
ADVANCE

23. Folded Mountains
http://freddoty.com/folded-mountains
near the Sullivan River in the Canadian Rockies
The Cape Fold Belt Mountains
http://www.geocaching.com/geocache/GC2CEJP_steytlerville-arch?guid=ff36205a-b979-422c-8266-f7f83ec4d884
BACK

24. BACK
Fault-block Mountains
Nepal

25. BACK

26. BACK
Subduction
http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/subduction.html

27. • Tension : two plates are pulled apart at
divergent boundaries
Results in:
• Sea-floor spreading (new sea floor is made)
• Trenches or rifts (gashes made from the pulling apart)
• Subsidence or faulting
• earthquakes
Thingvellir Breach, Iceland
VIDEO: Sea Floor
Spreading- Nye (3 min)

28. • Shear : two plates slide past each other horizontally in a
transform boundary
Results in:
• Ridges
• earthquakes
San Andreas Fault, Ca

29. ROCK CYCLE
• Rock Cycle: process by which new crust is continually being
recycled
At plate boundaries:
-pull apart (making
new crust)
-push together
(forming mountains)
-subduct (under other plates)
http://www.perfecthomepictures.com/277773-gabbro-igneous-intrusive-phaneritic

30. PROCESSES:
1. crystallization
2. heat & pressure
3. weathering/erosion/deposition
4. Compaction/cementation
5. Melting
-VIDEO: Rock types & Rock Cycle (4min)
-ACTIVITY LINK
http://www.passmyexams.co.uk/GCSE/physics/rock-cycle.html

31. • Igneous rock: rock formed from cooling magma
• Intrusive igneous: crystalizes inside the earth slowly (hot in
there) making larger crystals
• Extrusive igneous: crystalizes fast outside the earth (cooler)
making fewer crystals
INTRUSIVE EXTRUSIVE
granite gabbro basalt obsidian

32. IGNEOUS ROCK FORMATION

33. • Metamorphic rock: rock is under heat & pressure for a long
time so that it chemically changes into another type of rock
granite
gneiss
sandstone
quartzite
slate
schist
coal
diamond

35. • Sedimentary rock: rock is formed over time by sediments
being compacted together
• Hold fossils that describe Earth’s early life forms
• The strata (layers) help determine relative age of rock
Clay sediment
makes shale
Sand sediment
makes sandstone
Mineral deposits in
water make
limestone
Dead plants & animals
make fossil fuels
Gravel, shell, &
fossils make
conglomerate

36. http://bc.outcrop.org/GEOL_B10/lecture11.html
SEDIMENTARY ROCK FORMATION

37. HOW OLD IS THE EARTH?
• Age of the Earth has been debated for Centuries
TRADITIONAL VIEW:
• At first scientists thought that the Earth was formed & has
been cooling ever since (not true)… led to wrong numbers
• They thought the earth was static & that only catastrophes led
to changes
• We now know earth has a heating mechanism inside causing
changes in the shape of the crust!

38. Despite these incorrect numbers, geologists had some correct
ideas too:
• Nicolas Steno 1660’s studied sedimentary rocks
Relative Dating
• Law of Superposition:
said that sediment layers (strata) are deposited in a
time sequence: oldest on bottom,
youngest on top
http://www.angelfire.com/az3/mohgameil/physical.html

39. • Unconformity places where no sediments were
preserved (erosion) for a time;
separates different ages
Angular unconformity

40. Grand Canyon,
Arizona

41. • Principle of original horizontality: said that layers of
sediment are originally deposited horizontally
• (therefore if they aren’t, something moved them
after they were laid down)
• Principle of cross-cutting relationships: says that a
feature is younger than the feature it cuts across

42. • William Smith 1790’s
• Hypothesized that if two layers of rock at different
locations contain similar fossils, then rocks must be the
same age
• Index fossils: fossils used
to determine relative age
of rocks

43. NEW CONTROVERSIAL IDEAS: 1800’s
• Charles Lyell 1830
• geologist who said the Earth’s features
were constantly changing & therefore
Earth was much older than previously thought
• (PEOPLE DID NOT LIKE IT)
• Uniformitarians: changes were constant and uniform:
processes at work in the past are still occurring today

45. MODERN DATING METHODS
1900 Radioactivity discovered (unstable atoms)
Absolute Dating
• Radiometric dating using radioactive forms of elements in rock
to determine the age of the rock or fossil

46. How it works:
• Atoms in an element have the SAME number of protons
• Sometimes their number of neutrons is different: isotopes
• Radioactive: unstable isotopes break down (decay) over time
• Decay happens at steady rate for each element
• Half-life: time it takes for ½ of the sample to decay (scientists
know for each element)
• Compare amount of parent isotope to daughter isotope to know
age of rock/fossil
Amount
Parent
isotope
Amount
Daughter
isotope
AGE OF
ROCK/FOSSIL

47. 50 %
25 %
25 %
25 %
50 %
100 %
50 %
PERCENTAGES
1/2
25 %
1/4
1/4
1/2
1
whole
1/2
FRACTIONS
RADIOACIVE DECAY

48. Common types:
Potassium-Argon
(> 1000,000 ya)
Uranium-Lead
(> 10 million ya)
Rubidium-Stronium
(>10 million ya)
Carbon-14 (in fossils)
VIDEO: Radiometric Dating (5 min)

49. VIDEO 3: Radiometric dating Geologic Time 5 min

50. Magnetic reversals: evidence is left in the
seafloor along divergent boundaries that the
Earth’s poles have reversed randomly many
times in Earth’s past
• New igneous rock, if it has metal in it will
magnetize
• There are places in the seafloor’s ‘record’
that are opposite to Earth’s current field
• This pattern is also seen in seafloor core
samples
• Important means of dating for
metamorphic & igneous rock samples (no
fossils)

51. • If rock becomes molten, radioactivity escapes & we can’t
determine age
• Rock Cycle???
• How old is the Earth?
• We use-
• Samples from Earth (oldest Zircon crystal found so far in
Australia)
• Samples from meteorites that hit Earth
• Samples from the moon
• Date the Sun based upon luminosity & Energy as
compared to other stars
• Ice core data…

52. … So most scientists agree that with current technology, the
Earth is…
4.5 billion years old
VIDEO: COSOMOS- The Clean Room (45 min)
VIDEO 1: Big Idea Age of the Earth 5 min
VIDEO 2: History of Earth in 5 ½ minutes 5.5 min
VIDEO 3: World’s Most Asked Questions-How old is the Earth? (2:50)