1. Understanding Earth: A Dynamic and Evolving Planet
Chapter 1
Understanding Earth:
A Dynamic and Evolving Planet

2. Introduction Atmosphere Biosphere Hydrosphere Lithosphere Mantle Core
Geology is a complex, integrated system of related parts, components, or sub-systems.
These interact in an organized fashion, affecting one another in various ways. The principal subsystems of the earth are the:
Atmosphere
Biosphere
Hydrosphere
Lithosphere
Mantle
Core
Figure 1.1, p. 5

3. Fig. 1-1, p. 5 Atmosphere Evaporation, condensation,
and precipitation transfer
water between atmosphere
and hydrosphere, influencing
weather and climate and
distribution of water.
Plant, animal, and human
activity affect composition of
atmospheric gases.
Atmospheric temperature and
precipitation help to determine
distribution of Earth’s biota.
Atmospheric gases and
precipitation contribute to
weathering of rocks.
Plants absorb and transpire water.
Water is used by people for domestic,
agricultural, and industrial uses.
Water helps determine abundance,
diversity, and distribution of
organisms.
Hydrosphere
Biosphere
Plate movement affects size,
shape, and distribution of
ocean basins. Running water
and glaciers erode rock and
sculpt landscapes.
Organisms break down rock
into soil. People alter the
landscape. Plate movement
affects evolution and
distribution of Earth’s biota.
Heat reflected from land surface affects
temperature of atmosphere. Distribution
of mountains affects weather patterns.
Figure 1.1: Subsystems of Earth.
The atmosphere, hydrosphere, biosphere, lithosphere, mantle, and core are all subsystems of Earth. This simplified diagram shows how these subsystems interact, with some examples of how materials and energy are cycled throughout the Earth system. The interactions between these subsystems make Earth a dynamic planet that has evolved and changed since its origin 4.6 billion years ago.
Convection cells within mantle contribute to movement of plates (lithosphere) and recycling of lithospheric material.
Plate
Mantle
Supplies heat
for convection
in mantle
Core
Fig. 1-1, p. 5

4. What is Geology?
Geology is the study of the Earth, other planets and their moons.
Physical geology is concerned with the materials and processes which compose and operate on the surface of, and within, Earth.
Historical geology is concerned with the origin and evolution of Earth's continents, oceans, atmosphere, and life.

5. What is geology? Geologists are employed in diverse occupations.
Principle occupations include:
Mineral and energy resource exploration
Solving environmental problems
Predicting natural disasters

6. Geology and the Formulation of Theories
What is a theory?
Derived from the scientific method, which involves:
gathering and analyzing facts
formulating hypotheses to explain the phenomenon
testing the hypotheses
and finally proposing a theory.
Science makes no claim about the existence or nonexistence of the supernatural.

7. Geology and the Formulation of Theories
In science, a theory is NOT a hunch or guess, but a reliable explanation supported by a large amount of evidence.
In geology, plate tectonics is an important theory.

8. Geology and the Formulation of Theories
What is a theory?
The hypotheses is a tentative explanation.
A scientific theory is a testable explanation for some natural phenomenon, that is supported by a large body of evidence.

9. How Does Geology Relate to the Human Experience?
Geology pervades our everyday lives and is a part of many aspects of human experience, including the arts and literature.
The range of environmental problems, resources, military tactics, and other issues of concern to society require a basic understanding of geology.
Figure 1.2, p. 6

10. How does geology affect our daily lives?
Natural Disasters
Economics and Politics
Our Role as Decision Makers
Consumers and Citizens
Sustainable Development
Figure 1.3, p. 7

11. Other minerals and metals
9203 kg
Clays
348 kg
Zinc
311,034 l
Petroleum
774,000 kg
Stone, sand,
and gravel
14,359 kg
Salt
159,880 m3
Natural gas
33,771 kg
Cement
>30,615 kg
Other minerals and metals
14,694 kg
Iron ore
410 kg
Lead
Figure 1.3: Lifetime Mineral Usage.
According to the Mineral Information Institute in Golden, Colorado, the average American born in 2006 has a life expectancy of 77.8 years and will need 1,672,393 kg of minerals, metals, and fuels to sustain his or her standard of living over a lifetime. That is an average of 21,496 kg of mineral and energy resources per year for every man, woman, and child in the United States.
2438 kg
Bauxite
(Aluminum)
260,530 kg
Coal
8301 kg
Phosphate rock
44 g
Gold
629 kg
Copper
Stepped Art
Fig. 1-3, p. 7

12. Global Geologic and Environmental Issues Facing Humankind
Most scientists would argue that overpopulation is the greatest problem facing the world today.
7 billion in 2011, perhaps 9 billion by 2045.
Increasingly large numbers of people must be fed, housed, and clothed, with a minimal impact on the environment.

13. Global Geologic and Environmental Issues Facing Humankind
Problems associated with overpopulation
Increased risks from earthquakes, tsunami, floods and volcanoes
More pollution
Wildlife threatened
Shortages of resources
Poverty

14. Global Geologic and Environmental Issues Facing Humankind
Greenhouse effect: Retention of heat in the atmosphere.
Humanity has been adding to the greenhouse.
This results in an increase in the temperature of Earth’s surface and atmosphere, thus producing global warming.
Figure 1.4, p. 8

15. Greenhouse Effect
a) Short-wavelength radiation from the Sun that is not reflected back into space penetrates the atmosphere and warms Earth’s surface.
b) Earth’s surface radiates heat in the form of long–wavelength radiation back into the atmosphere, where some of it escapes into space. The rest is absorbed by greenhouse gases and water vapor and reradiated back toward Earth.
c) Increased concentrations of greenhouse gases trap more heat near Earth’s surface, causing a general increase in surface and atmospheric
temperatures, which leads to global warming.
Figure 1.4: The Greenhouse Effect and Global Warming.
Stepped Art
Fig. 1-4, p. 8

16. Origin of the Universe Did it begin with a Big Bang?
In the Big Bang theory, the universe began approximately 14 billion years ago.
An extremely dense, hot body of matter expanded and cooled

17. Origin of the Universe How do we know? Evidence for the Big Bang:
the universe is expanding from a central point.
The entire universe has a pervasive and constant background radiation, thought to be the faint afterglow of the Big Bang.
Fig. 1.7, p. 10

18. Origin of the Universe
Evidence for the Big Bang: Expansion of the Universe
Objects farther from the Earth are moving faster away from us.
Confirmed with the Doppler Effect.
Fig. 1.6, p. 10

19. Our Solar System Sun: a star
8 planets (Pluto no longer considered a planet)
Numerous moons, asteroids and comets
About 4.6 billion years old
Figure 1.8, p. 11

20. Our Solar System: Its Origin and Evolution
Formed from a rotating cloud (nebula) of matter about 4.6 billion years ago.
The cloud condensed, collapsed from gravity and flattened into a rotating disk.
The Sun, planets, and moons formed within this disk.
Figure 1.9, p. 12

21. Earth: Its Place in Our Solar System
Earth condensed as a solid body from the solar nebula about 4.6 billion years ago.
Soon after internal heat differentiated the Earth into a layered planet.
Fig. 1.10, p. 13

22. Why Earth is a Dynamic and Evolving Planet
Earth has continuously changed during its 4.6 billion year existence as a result of interactions between its various subsystems and cycles.

23. Why Earth is a Dynamic and Evolving Planet
As the earth differentiated, 3 concentric layers formed.
Crust
Mantle
Core.
Fig. 1.11, p. 13

24. Why Earth is a Dynamic and Evolving Planet
The Core
The core consists of
a small, solid inner region
a larger, liquid, outer portion
Composed of iron and a small amount of nickel.
Fig. 1.11, p. 13

25. Why Earth is a Dynamic and Evolving Planet
The Mantle
The mantle surrounds the core and is divided into:
a solid lower mantle
a partially molten asthenosphere that overall behaves plastically and flows slowly
a solid upper mantle.
Composed primarily of peridotite, an igneous rock made of olivine.
Fig. 1-11, p. 13

26. Why Earth is a Dynamic and Evolving Planet
The Crust
The outermost layer, the crust,
is divided into:
thick continental crust
thin oceanic crust
Fig. 1.11, p. 13

27. Why Earth is a Dynamic and Evolving Planet
The Asthenosphere
Surrounds the lower mantle
Behaves plastically and slowly flows
Partial melting in the asthenosphere generates magma (molten rock) that rises to the earth’s surface.
Fig. 1.11, p. 13

28. Why Earth is a Dynamic and Evolving Planet
The Lithosphere
The crust and upper mantle make up the lithosphere which forms the solid outer layers of the Earth.
Fig. 1.11, p. 13

29. Why Earth is a Dynamic and Evolving Planet
Plate Tectonic Theory
The lithosphere is composed of rigid plates that diverge, converge, or slide sideways past one another as they move over the asthenosphere
Fig. 1.12, p. 16

30. Convection cell Outer core Inner core
Mid-oceanic ridge
Trench
Ocean
Subduction
Oceanic
lithosphere
Continental
lithosphere
Hot
Cold
Convection
cell
Upwelling
Figure 1.11: Movement of Earth’s Plates.
Earth’s plates are thought to move partially as a result of underlying mantle convection cells in which warm material from deep within Earth rises toward the surface, cools, and then upon losing heat, descends back into the interior as shown in this diagrammatic cross section.
Outer
core
Mantle
Inner
core
Stepped Art
Fig. 1-12, p. 16

31. Why Earth is a Dynamic and Evolving Planet
Plate Tectonic Theory: The Plates
Fig. 1.13, p. 16

32. Why Earth is a Dynamic and Evolving Planet
Plate Tectonic Theory: Boundaries between Plates
Volcanoes and earthquakes occur at the boundaries between the plates.
Fig. 1.14, p. 17

33. Why Earth is a Dynamic and Evolving Planet
Plate Tectonics and Earth Systems
Plate tectonic theory is a unifying explanation for many geologic features and events, helping us understand the composition and internal processes of Earth on a global scale.
Add Table 1.3, p.20

34. The Rock Cycle Igneous Sedimentary Metamorphic
A rock is a solid aggregate of one or more minerals, as well as non-crystalline matter such as natural glass or organic material like coal.
Three major groups of rocks:
Igneous
Sedimentary
Metamorphic
Fig. 1.15, p. 18

35. Intrusive Igneous Rock Extrusive Igneous Rock
The Rock Cycle
Igneous Rocks form from the crystallization of cooling magma or the consolidation of volcanic ejecta.
Intrusive igneous rock crystallizes beneath the Earth’s surface.
Extrusive igneous rock crystallizes and cools at the earth’s surface. At times it cools so fast that it forms a glass or ash.
Granite
Intrusive Igneous Rock
Basalt
Extrusive Igneous Rock
Fig a-b, p. 19

36. Forms from river gravels Precipitation from seawater
The Rock Cycle
Sedimentary Rocks typically layered deposits formed from:
rock/mineral fragments
precipitation of minerals from solution
the compaction of plant and animal remains.
Conglomerate
Forms from river gravels
Limestone
Precipitation from seawater
Fig c-d, p. 19

37. The Rock Cycle
Metamorphic Rocks form from alteration of other rocks, usually by:
Heat
Pressure
Chemically active fluids
Gneiss
Quartzite
Fig e-f, p. 19

38. The Rock Cycle
The rock cycle illustrates the interactions between Earth’s internal and external processes and how the three rock groups are interrelated.
Fig. 1.15, p. 18

39. The Rock Cycle How are the rock cycle and plate tectonics related?
Plate movement is the driving mechanism of the rock cycle. Plate interaction determines, to some extent, which of the three rock groups will form.
Fig. 1.17, p. 20

40. Organic Evolution and the History of Life
The theory of organic evolution states:
that all living things are related
have descended with modification from organisms living in the past.
Charles Darwin proposed that the mechanism of natural selection results in survival to reproductive age of organisms best suited to their environment.
Fossils, the remains of once-living organisms provide evidence for evolution and a history of life before humans.

41. Organic Evolution and Plate Tectonics
Together the theories of plate tectonics and organic evolution have changed the way we view our planet.

42. Geologic Time
An appreciation of the immensity of geologic time is central to understanding the evolution of the Earth and its life.
Earth goes through cycles of much longer duration than the human perspective of time
The geologic time scale is the calendar that geologists use to date past events in Earth’s history.
Fig. 1.18, p. 22

43. Geologic Time
Fig. 1.18, p. 22

44. Geologic Time and Uniformitarianism
Uniformitarianism forms a cornerstone of geology. It is a fundamental tenet of geology.
This principle states that the laws of nature have remained unchanged through time and thus, that the processes observed today have also operated in the past, though possibly at different rates.
Therefore, to understand and interpret geologic events from evidence preserved in rocks, geologists must first understand present-day processes in rocks.

45. How does the study of geology benefit us?
Understanding how the Earth’s subsystems work will help ensure the survival of the human species.
It will help us to understand how our actions affect the delicate balance between these systems.

46. End of Chapter 1