1. geology
Geology is the study of Earth in all of its physical, chemical and biological dimensions

2. Accretion of planetesimals
Protosun fuses hydrogen, becomes the Sun, solar pressure clears away planet-building materials
Current solar system
Accretion of planetesimals
Figure 1.9: The currently accepted theory for the origin of our solar system involves (a) a huge nebula condensing under its own gravitational attraction, then (b) contracting, rotating, and (c) flattening into a disk, with the Sun forming in the center and eddies gathering up material to form planets. As the Sun contracted and began to visibly shine, (d) intense solar radiation blew away unaccreted gas and dust until finally (e) the Sun began to burn hydrogen and the planets were formed.
Protoplanetary disk rotates faster, flattens, and protosun develops
Solar nebula collapses and rotates
Fig. 1-9, p. 13

3. Learning Objectives Explain how the Earth systems or spheres interact.
Explain the Earth’s internal and external energy sources
Identify the the Earth’s composition (surface and interior)
Identify the eons, eras, periods, and epochs on the geologic time scale.
Relate geologic time to the evolution of the Earth.

4. THE EARTH: Systems or Spheres
The Earth is a dynamic, ever-changing planet.
Earth is a complex, integrated system.
The Earth has four spheres that are subsystems of the larger Earth system.
Each sphere is connected to the other by processes or cycles.
The internal and external energy sources of the Earth are the driving mechanism for change.

5. Figure 1.2: A series of gears can be used to illustrate how some of Earth’s systems and processes interact. Pistons and driving rods represent energy sources or driving mechanisms, large gears represent important processes or cycles, and small gears represent connecting processes or relationships. Pulleys are used to show relationships to other systems. Although gears are a useful way to represent systems diagrammatically, remember that real Earth systems are far more complex.
Fig. 1-2, p. 4

6. Figure 1.3: The atmosphere, biosphere, hydrosphere, lithosphere, mantle, and core are all subsystems of Earth. The interactions among these subsystems make Earth a dynamic planet, which has evolved and continues to change since its origin 4.6 billion years ago.
Fig. 1-3, p. 5

7. The Different “Spheres”
Atmosphere (atmos means ____)
Hydrosphere (hydro means ____)
Biosphere (bio means ____)
Lithosphere (litho means ____)
Using Figure 1-3, explain the interactions between the different spheres. Using examples, explain four different interactions between any of the four spheres.

8. Table 1-1, p. 5

9. Earth and Energy
Energy is required for the Earth’s spheres to interact.
External Energy Source
The Sun
Internal Sources
Heat leftover from formation
Heat from gravitational contraction
Heat from extraterrestrial impacts
Decay of radioactive elements
Friction from the movement of the plates and convection in the mantle

10. Decay of Radioactive Elements
Unstable element such as Uranium 238 decays to Lead 206
Earth has cooled over time as radioactive elements decay to stable elements.

11. Differentiation
More dense material sinks (molten iron and nickel)
leaving the less dense material (silicates) near the surface
Figure 1.10: (a) Early Earth was probably of uniform composition and density throughout. (b) Heating of the early Earth reached the melting point of iron and nickel, which, being denser than silicate minerals, settled to Earth’s center. At the same time, the lighter silicates flowed upward to form the mantle and the crust. (c) In this way, a differentiated Earth formed, consisting of a dense iron-nickel core, an iron-rich silicate mantle, and a silicate crust with continents and ocean basins.
Gases emitted from the interior during this process are likely the source for the formation of the atmosphere and oceans.
Fig. 1-10, p. 14

12. The Earth’s Layers
Earth layers result from density differences between the layers caused by variations in composition, temperature, and pressure.
Core: metal (Fe and small amount of Ni) [10-13 g/cm3]
Outer liquid core
Inner solid core
Mantle: iron-rich rock (FeMg-Peridotite) [3.3–5.7 g/cm3]
Crust: aluminum and magnesium rich rock
Continental Crust: SiAl (rock) less dense [2.7 g/cm3]
Oceanic Crust: SiMa (rock) more dense [3.0 g/cm3]

13. Components of the Earth’s Crust
Elements (Si and O are most abundant, traces of radioactive elements)
Minerals (naturally occurring, inorganic crystalline solids, gemstones, metals)
Rocks (igneous, sedimentary and metamorphic) Rocks are composed of minerals.
Natural resources/fossil fuels (coal, natural gas and oil)
Soils (weathered rock, air, water and organic material)

14. Lithosphere and Asthenosphere
Lithosphere is the solid, brittle outer layer of the Earth composed of:
Oceanic and continental crust
Top part of the mantle
Asthenosphere is the plastic layer of the mantle directly below the lithosphere over which the lithospheric plates move.
The lithosphere is broken into many pieces called plates.

15. Figure 1.11: A cross section of Earth, illustrating the core, mantle, and crust. The enlarged portion shows the relationship between the lithosphere (composed of the continental crust, oceanic crust, and solid upper mantle) and the underlying asthenosphere and lower mantle.
Fig. 1-11, p. 15

16. 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.

17. 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.

18. Geologic Time Scale Ages in millions of years Today’s Geologic Date:
Recent Epoch
Quaternary Period
Cenozoic Era
Phanerozoic Eon
Figure 1.18: The geologic time scale. Numbers to the right of the columns are ages in millions of years before the present.
The Earth is currently experiencing an interglacial episode
Fig. 17-1, p. 394

19. CHAPTER SUMMARY
We can view Earth as a system of interconnected components that interact and affect one another. The principal subsystems of Earth are the atmosphere, hydrosphere, biosphere, lithosphere, mantle, and core. Earth is considered a dynamic planet that is continuously changing because of the interactions among its various subsystems and cycles.
Geology, the study of Earth, is divided into two broad areas: Physical geology is the study of Earth materials as well as the processes that operate within and on Earth’s surface; historical geology examines the origin and evolution of Earth, its continents, oceans, atmosphere, and life.
Geology is part of the human experience. We can find references to it in the arts, music, and literature. A basic understanding of geology is also important for dealing with the many environmental problems and issues facing society.
Geologists engage in a variety of occupations, the main one being exploration for mineral and energy resources. They are also becoming increasingly involved in environmental issues and making shortand long-range predictions of the potential dangers from such natural disasters as volcanic eruptions and earthquakes.

20. CHAPTER SUMMARY
About 4.6 billion years ago, the solar system formed from a rotating cloud of interstellar matter. Eventually, as this cloud condensed, it collapsed under the influence of gravity and flattened into a rotating disk. Within this rotating disk, the Sun, planets, and moons formed from the turbulent eddies of nebular gases and solids.
Earth is differentiated into layers. The outermost layer is the crust, which is divided into continental and oceanic portions. Below the crust is the solid portion of the upper mantle. The crust and solid part of the upper mantle, or lithosphere, overlie the asthenosphere, a zone that slowly flows. The asthenosphere is underlain by the solid lower mantle. Earth’s core consists of an outer liquid portion and an inner solid portion.
The scientific method is an orderly, logical approach that involves gathering and analyzing facts about a particular phenomenon, formulating hypotheses to explain the phenomenon, testing the hypotheses, and finally proposing a theory. A theory is a testable explanation for some natural phenomenon that has a large body of supporting evidence.
The lithosphere is broken into a series of plates that diverge, converge, and slide sideways past one another.

21. CHAPTER SUMMARY
Plate tectonic theory provides a unifying explanation for many geologic features and events. The interaction between plates is responsible for volcanic eruptions, earthquakes, the formation of mountain ranges and ocean basins, and the recycling of rock material.
The rock cycle illustrates the interactions among internal and external Earth processes and shows how the three rock groups are interrelated.
Igneous, sedimentary, and metamorphic rocks are the three major groups of rocks. Igneous rocks result from the crystallization of magma or the consolidation of volcanic ejecta. Sedimentary rocks are formed mostly by the consolidation of rock fragments, precipitation of mineral matter from solution, or compaction of plant or animal remains. Metamorphic rocks are produced from other rocks, generally beneath Earth’s surface, by heat, pressure, and chemically active fluids.
Time sets geology apart from the other sciences, except astronomy, and an appreciation of the immensity of geologic time is central to understanding Earth’s evolution. The geologic time scale is the calendar geologists use to date past events.
The principle of uniformitarianism is basic to the interpretation of Earth history. This principle holds that the laws of nature have been constant through time and that the same processes that operate today have operated throughout the past, though at different rates.