GLG101 Physical Geology Spring 2010 Thomas D. Hoisch http://jan.ucc.nau.edu/~tdh5/glg101_S10.htm

NAU Geology Club Contact: Carmen Winn, clw264@nau.edu

The Science of Geology Geology, people, and the environment Problems and issues addressed by geology include Natural hazards, resources, and environmental issues

The Science of Geology Some historical notes about geology The nature of Earth has been a focus of study for centuries Catastrophism Uniformitarianism and the birth of modern geology

What is Geology? Geology vs. other sciences Physical Geology What do geologists do?

Table 1.1

Figure 1.2

Figure 1.7B

Geologic time Absolute ages: Geologists are now able to determine fairly accurate dates for events in Earth history Relative ages: Relative dating means that dates are placed in their proper sequence or order without knowing their specific age

Geologic time The magnitude of geologic time Involves vast times – millions or billions of years Many processes are very gradual

The nature of scientific inquiry How or why things happen are 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 Paradigm - a theory with broad implications

The nature of scientific inquiry Scientific methods involves Gathering facts through observations Formulation of hypotheses and theories

Science – a definition: “Science is the acceptance of what works and the rejection of what does not” …Jacob Bronowski - mathematician

Earth as a system *Hydrosphere Atmosphere Biosphere **Solid Earth Outer space?

Figure 1.5

Early Earth Evolution Big Bang According to NASA WMAP mission – occurred at 13.7 Ga First stars appears 200 m.y. later

Early evolution of Earth Origin of planet Earth Most researchers believe Earth and 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

Early evolution of Earth Origin of planet Earth Most researchers believe Earth and 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

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)

Early evolution of Earth Formation of Earth’s layered structure: the “Great Catastrophe” 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

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

Earth’s Layered structure Figure 1.16

Figure 1.14A

Figure 1.14B

The face of Earth Earth’s surface Continents Continents: average elevation 0.5 miles Oceans: average depth 2.4 miles Continents Mountain belts Most prominent feature of continents The stable interior Also called a craton – composed of shields and stable platforms

Figure 1.16

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

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

Figure 1.15Left

Figure 1.15Right

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

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

Rocks and the rock cycle The Rock Cycle: One of Earth’s subsystems One rock changes to another and back with time Materials change both on the surface and inside the Earth

The Rock Cycle Figure 1.23

End of Chapter 1