1. ESC 102
Historical
Geology
Fall 2010

2. Spheres of the Earth
When we view the Earth from space what Earth systems are observable?
What is most obvious?
Are these systems independent or do they interact with one another?

4. Spheres of the Earth Lithosphere: Earth’s solid rocky mass
Hydrosphere: All of earth’s water
Atmosphere: The thin gaseous layer above Earth’s surface
Biosphere: All of earth’s life forms

5. Historical Geology: A study of the dynamic and evolving Earth
Changes in its surface
Changes in life

6. Three Themes dominate the story of the evolving Earth
Solid Earth is composed of plates that move over Earth’s surface over time. This is explained by the Theory of Plate Tectonics
Earth’s biota – all of living things – has evolved or changed through history and is explained by the Theory of Organic Evolution
All of the geologic processes take place within an extensive geologic time scale spanning 4.6 billion years of Earth’s history

7. Historical Geology applies geologic principles to help predict and explain Earth’s materials
William Smith was an English surveyor who realized that rock types and fossils occur in repeated patterns. He was able to predict rock sequences that would be encountered in constructing canals
Smith mapped the geology of much of England. (1815)

8. This map took many years to complete and helped establish the geologic time scale.

9. Hypothesis or Theory?
The scientific method brings an orderly and logical approach to decoding geologic evidence.
A hypothesis is a tentative explanation for observations
Scientists make predictions using hypotheses – then they are tested
After repeated testing, a theory may be proposed
Some phenomena cannot be tested or explained

10. A theory is formed A theory is more than an “educated guess”
A theory explains natural phenomena and may relate several observations
A theory is well-tested and well-supported by objective evidence
Examples include the Plate Tectonics Theory and the Theory of Organic Evolution

11. Where do scientists look for evidence for the following?
The origin and age of the universe
The origin and age of the solar system
The origin and age of the Earth and Moon
The origin of life on Earth
Evidence of plate movement on Earth
Explanation for large scale extinctions on Earth

12. How old is the universe?
When? Scientists believe the universe was formed about 15 billion years ago
How? The Big Bang is a model for the “beginning” of the universe
“Show me”! What is the evidence?

13. Evidence of the Big Bang
Pervasive background radiation of 2.7o
above absolute zero is observed in space (-273o C or -460o F)
--Afterglow of the Big Bang
Galaxies moving away – expanding universe
Determine the Age of the Universe
*Determine rate of expansion *Backmodel to a time when the galaxies would be together in space

14. Big Bang hypothesis Initial state: NO time, NO matter, NO space
Universe was pure ENERGY
During the FIRST second of time:
--very dense matter came into existence
--The four basic forces separated:
gravity, electromagnetic force, strong and weak nuclear forces
--Enormous expansion occurred

15. Big Bang Model 300,000 years later: Next 200 million years:
Atoms of hydrogen and helium formed
Light (photons) burst forth for the first time
Next 200 million years:
Continued expansion
Stars and galaxies began to form
Elements heavier than hydrogen and helium began to form with stars by nuclear fusion

16. Origin of Our Solar System
Solar nebula theory
cloud of gases and dust
formed a rotating disk
condensed and collapsed due to gravity
forming solar nebula
with an embryonic Sun
surrounded by a rotating cloud

17. Embryonic Sun and Rotating Cloud
Planetesimals have formed
in the inner solar system,
and large eddies of gas and dust
remain far from the protosun

18. The planets formed with distinct orbits around the sun
The planets formed with distinct orbits around the sun. Some planets have satellites which orbit individual planets.

19. The Planets Terrestrial Jovian Mercury Venus Earth Mars Asteroid Belt
Small in size.
Composed of rock.
Metallic cores.
Asteroid Belt
Jovian
Jupiter
Saturn
Uranus
Neptune
Large in size.
Composed of hydrogen, helium, ammonia, methane
Small rocky cores
Pluto: no longer has planet status

21. Earth’s Very Early History
Started out cool about 4.6 billion years ago
probably with uniform composition/density
Mostly:
silicate compounds
iron and magnesium oxides
Temperature increased. Heat sources:
meteorite impacts
gravitational compression
radioactive decay
Heated up enough to melt iron and nickel

22. The earth and moon were heavily bombarded in Earth’s early history.

23. Earth’s Differentiation
Differentiation = segregated into layers of differing composition and density
Early Earth was probably uniform
After heating, molten iron and nickel sank to form the core
Lighter silicates flowed up to form mantle and crust

24. Forming the Moon Impact by Mars-sized planetesimal with early Earth
4.6 to 4.4 billion years ago
Ejected large quantity of hot material
Formed the moon

25. Most of the lunar material
came from the mantle of the colliding planetesimal
The material cooled and
crystallized into lunar layers
Moon is smaller than Earth and cooled quickly. Light colored surface areas are lunar
Highlands – heavily cratered.
Evidence of massive meteorite
Bombardment
Mare are areas of lava flows, more likely due to impact than tectonics

26. Earth—Dynamic Planet Earth was also subjected
to the same meteorite barrage
that pock-marked the Moon
Why isn’t Earth’s surface also densely cratered?

27. Earth—Dynamic Planet Earth was also subjected
to the same meteorite barrage
that pock-marked the Moon
Why isn’t Earth’s surface also densely cratered?
Because Earth is a dynamic and evolving planet
Craters have long since been worn away

28. Earth’s Interior Layers
Lithosphere
solid upper mantle and crust
broken into plates that move over the asthenosphere
Asthenosphere
part of upper mantle
behaves plastically and slowly flows

29. Plate Tectonic Theory
Lithosphere is broken into individual pieces called plates
Plates move over the asthenosphere
as a result of underlying convection cells

30. Plate Tectonic Theory Movement at plate boundaries At plate boundaries
plates diverge
plates converge
plates slide sideways past each other
At plate boundaries
Volcanic activity occurs
Earthquakes occur

31. Modern Plate Map Active tectonic boundaries are in red

32. Plate Tectonic Theory
After decades of puzzling evidence, the theory was developed in the1960s
Provides a framework for
interpreting many aspects of Earth on a global scale
relating many seemingly unrelated phenomena
interpreting Earth history The “unifying theory of geology”

33. Plate Tectonics and Earth Systems
Mechanism: Plate tectonics is driven by convection in the mantle
and in turn drives mountain building
and associated igneous and metamorphic activity
Global effects of plate movement: Arrangement of continents affects
solar heating and cooling,
winds and weather systems
Rapid plate spreading and hot-spot activity
may release volcanic carbon dioxide
and affect global climate

34. History of Earth
The history of the early earth through the present is revealed mainly in the rock and fossil records.
By applying principles of formation and determining environments from life forms, early interpretations about Earth’s land masses and oceans have been made

35. Theory of Organic Evolution
Provides a framework for understanding the history of life
Darwin’s
On the Origin of Species by Means of Natural Selection, published in 1859,
revolutionized biology
Provided the mechanism of natural selection

36. Central Thesis of Evolution
All present-day organisms
are related and descended from organisms that lived during the past
Natural selection is the mechanism
that accounts for evolution
Natural selection results in the survival
to reproductive age of those organisms
best adapted to their environment

37. History of Life The fossil record provides perhaps
the most compelling evidence
in favor of evolution
Fossils are the remains or traces
of once-living organisms
Fossils demonstrate that Earth
has a history of life

38. Geologic Time From the human perspective time units are in
seconds, hours, days, years
Ancient human history
hundreds or even thousands of years
Geologic history
millions, hundreds of millions, billions of years

39. Geologic Time Scale
Resulted from the work of many 19th century geologists who
pieced together information
from numerous rock exposures,
constructed a sequential chronology
based on changes in Earth’s biota through time
The time scale was subsequently dated in years
using radiometric dating techniques

40. Geologic Time Scale

41. Uniformitarianism: The Present is the key to the past
Uniformitarianism is a cornerstone of geology
is based on the premise that present-day processes
have operated throughout geologic time
The physical and chemical laws of nature
have remained the same through time
To interpret geologic events
from evidence preserved in rocks
we must first understand present-day processes
and their results
Rates and intensities of geologic processes
may have changed with time