1. An Introduction to Geology

2. The Science of Geology
Geology - the science that pursues an understanding of planet Earth
Physical geology - examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface
Historical geology - seeks an understanding of the origin of Earth and its development through time

3. The Science of Geology Geology, people, and the environment
Many important relationships exist between people and the natural environment
Problems and issues addressed by geology include
Natural hazards, resources, world population growth, and environmental issues

4. Geologic time
Geologists are now able to assign fairly accurate dates to events in Earth history (absolute dating)
Relative dating and the geologic time scale
Relative dating means that dates are placed in their proper sequence or order without knowing their age in years

5. The geologic time scale
Figure 1.7

6. Precambrian 4.6 billion years to 544 million years.
Represents 88% of all of the history of the earth.
Referred to as the Cryptozoic Eon.
“hidden life”
(no more BIFs)
(prokaryotes)

7. Precambrian: The First 4 Billion Years
88% of geologic time

8. Geologic time The magnitude of geologic time
Involves vast times – millions or billions of years
An appreciation for the magnitude of geologic time is important because many processes are very gradual (uniformitarianism)
Earth 4.6 Billion Years Old

9. The nature of scientific inquiry
Science assumes the natural world is consistent and predictable
Goal of science is to discover patterns in nature and use the knowledge to make predictions
Scientists collect data through observation and measurements

10. The nature of scientific inquiry
How or why things happen is explained using a
Hypothesis – a tentative (or untested) explanation
Theory – a well-tested and widely accepted view that the scientific community agrees best explains certain observable facts
Law-a general observation that holds true without explaining why it holds true

11. The nature of scientific inquiry
Scientific method involves
Gathering facts through observations (data)
Formulation of hypotheses and theories
There is no fixed path that scientists follow that leads to scientific knowledge

12. A view of Earth Earth is a planet that is small and self-contained
Earth’s four spheres
Hydrosphere
Atmosphere
Biosphere
Solid Earth

13. Earth’s Spheres ATMOSPHERE Air BIOSPHERE Living Things Atmosphere
Contains all the air in Earth’s system.
BIOSPHERE Living Things
Contains all of Earth’s living things— microorganisms, plants, and animals.
Atmosphere
LITHOSPHERE Land
Contains all the cold, hard, solid land of Earth’s crust (surface), the semi-solid land underneath the crust, and the liquid land near the center.
HYDROSPHERE Water
Contains all the solid, liquid, and gaseous water of Earth.

14. What is the Biosphere?
All regions of the Earth that are capable of supporting life.
Evolved about 3.5 billion years ago
20-30 km thickness (deep ocean trenches into the atmosphere)
Includes portions of the hydrosphere, lithosphere, atmosphere, and cryosphere.

15. The biosphere is the total of all of Earth's ecosystems
The global ecosystem is called the biosphere
It is the sum of all the Earth's ecosystems
The biosphere is the most complex level in ecology
Figure 34.2A

16. The Biosphere We divide the total biosphere into three parts
the Atmosphere
the Hydrosphere
the Lithosphere

17. The Biosphere
It is the physical and chemical parameters of each habitat that selects for the autochthonous community.

18. The Biosphere
The Biosphere (a.k.a. Ecosphere) - the totality of life on earth and the abiotic surroundings that is inhabited.
Earth minus sterile areas:
strata below the crust
upper atmosphere
habitats of extreme heat or lacking liquid water

19. Hydrosphere The earth’s water is found as a
LIQUID in rivers, lakes, oceans, rain
GAS in our atmosphere
SOLID in snow and ice
71% of the earth’s surface is covered by water

20. Hydrosphere
Liquid
Gas
Solid

21. Water Distribution

22. Processes of the Hydrologic Cycle
Evaporation - the transformation of water from a solid or liquid to a gaseous state
Condensation - transformation of vapor into a liquid
Precipitation - liquid or solid water that falls from the atmosphere to the earth’s surface

23. The Hydrosphere Freshwater Limnetic Habitats (Limnology)
2. Lotic Habitats (running water)
a. Springs
b. Streams
c. Rivers

24. The Hydrosphere Freshwater - Lake Zonation euphotic zone littoral zone
surface
limnetic zone (P>R) 
profundal zone (P>R)
 compensation depth

26. Oceans

27. 0.5% Groundwater
0.02% Rivers and Lakes

29. Structure of Atmosphere
From Cunningham & Cunningham, 2004, Fig. 9.1

30. Atmospheric Composition % by Volume
Major Constituents
Nitrogen 78.1
Oxygen 20.9
Active Minor Constituents
Water vapor (H2O) variable (0.48 aver.)
Carbon Dioxide (CO2) 0.035
Methane (CH4)
Nitrous oxide (NO2)
Ozone (O3)
CFC’s
H2O (liq & ice)
Inactive Minor Constituents
Argon
Neon
Helium
Krypton
Xenon
Hydrogen

31. Other Components of the Atmosphere
Water Droplets
Ice Crystals
Sulfuric Acid Aerosols
Volcanic Ash
Windblown Dust
Sea Salt
Human Pollutants

32. Structure of the Atmosphere
Defined by Temperature Profiles
Troposphere
Where Weather Happens
Stratosphere
Ozone Layer
Mesosphere
Thermosphere
Ionosphere

33. Troposphere
This is the layer that is closest to the surface of the earth
It’s elevation ranges from 0 to 10 km

34. Stratosphere This layer sits on top of the troposphere
It’s elevation ranges from 10 km to around 25 km
This layer contains the ozone layer, which protects us from harmful sunlight

35. Mesosphere This layer is above the stratosphere
It’s elevation ranges from 25 to 100 km

36. Thermosphere This is the highest layer of the atmosphere
It’s height ranges from 100 to 400 km
This is where most small meteorites burn up and is also the location in the atmosphere that the northern lights occur (aurora borealis)

37. Why is the Mesosphere so Cold?
Stratosphere warmed because of ozone layer
Thermosphere warmed by atoms being accelerated by sunlight
Mesosphere is sandwiched between two warmer layers

38. Composition and Altitude
Up to about 80 km, atmospheric composition is uniform (troposphere, stratosphere, mesosphere)
This zone is called the homosphere
Above 80 km light atoms rise
This zone is sometimes called the heterosphere

39. The surrounding air of the Earth
Atmosphere
The surrounding air of the Earth

40. Earth as a system
Earth is a dynamic planet with many interacting parts or spheres
Earth System Science
Aims to study Earth as a system composed of numerous interacting parts or subsystems
Employs an interdisciplinary approach to solve global environmental problems

41. Earth as a system
The Earth system is powered by the Sun that drives external processes in the
Atmosphere
Hydrosphere
At Earth’s surface
The Earth system is also powered by Earth’s interior

42. Earth as a system What is a system Feedback mechanisms
Any size group of interacting parts that form a complex whole
Open vs. closed systems
Feedback mechanisms
Negative feedback – maintains the status quo
Positive feedback – enhances or drives changes

43. Early evolution of Earth
Origin of planet Earth
Most researchers believe that Earth and the other planets formed at essentially the same time
Nebular hypothesis
Rotating cloud called the solar nebula
Composed of hydrogen and helium
Nebula began to contract about 5 billion years ago

44. Early evolution of Earth
Origin of planet Earth
Nebular hypothesis
Assumes a flat, disk shape with the protosun (pre-Sun) at the center
Inner planets begin to form from metallic and rocky substances
Larger outer planets began forming from fragments of ices (H2O, CO2, and others)

45. The Nebular Hypothesis

47. Early evolution of Earth
Formation of Earth’s layered structure
Metals sank to the center
Molten rock rose to produce a primitive crust
Chemical segregation established the three basic divisions of Earth’s interior
Primitive atmosphere evolved from gases in Earth’s interior

48. Early evolution of Earth
How did Earth become density stratified?
 Young Earth was probably homogeneous
 Heat and gravitational pressure caused Earth to partially melt
 Gravity then pulled the iron present into the center of Earth
 This heated Earth further
 Lighter minerals migrated to Earth’s surface and formed the crust
 lasted ~100 million years

49. Earth’s internal structure
Layers defined by composition
Crust
Mantle
Core
Layers defined by physical properties
Lithosphere
Asthenosphere
Mesosphere
Inner and Outer Core

50. Earth’s layered structure
Figure 1.14

51. Earth Stats Mass (kg) 5.976e+24 Mass (Earth = 1)
Equatorial radius (km) 6,378.14
Equatorial radius (Earth = 1) 1.0
Mean density (gm/cm^3)
Mean distance from the Sun (km) 149,600,000
Mean distance from the Sun (Earth = 1)
Rotational period (days)
Rotational period (hours)
Orbital period (days)
Mean orbital velocity (km/sec)
Orbital eccentricity
Tilt of axis (degrees)
Orbital inclination (degrees)
Equatorial escape velocity (km/sec)
Equatorial surface gravity (m/sec^2) 9.78
Visual geometric albedo 0.37
Mean surface temperature 15°C
Atmospheric pressure (bars)
Atmospheric composition
Nitrogen 77
Oxygen 21
Earth Stats

52. The face of Earth Earth’s surface Continents Oceans Mountain belts
Most prominent feature of continents
The stable interior
Also called a craton – composed of shields and stable platforms

53. The face of Earth Ocean basins Continental margins Deep-ocean basins
Includes the continental shelf, continental slope, and the continental rise
Deep-ocean basins
Abyssal plains
Oceanic trenches
Seamounts

54. The face of Earth Ocean basins Oceanic ridge system
Most prominent topographic feature on Earth
Composed of igneous rock that has been fractured and uplifted

55. End of Chapter 1

56. Rocks and the rock cycle
Basic rock types
Igneous rocks
Cooling and solidification of magma (molten rock)
Examples include granite and basalt
Sedimentary rocks
Accumulate in layers at Earth’s surface
Sediments are derived from weathering of preexisting rocks

57. Rocks and the rock cycle
Basic rock types
Sedimentary rocks
Examples include sandstone and limestone
Metamorphic rocks
Formed by “changing” preexisting igneous, sedimentary or other metamorphic rocks
Driving forces are increased heat and pressure
Examples include gneiss and marble

58. Rocks and the rock cycle
The Rock Cycle: One of Earth’s subsystems
The loop that involves the processes by which one rock changes to another
Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth

59. The
rock
cycle
Figure 1.21