What is geology? * Physical geology- examines earth materials and seeks to understand that many processes that operate on our planet * Historical geology- seeks an understanding of the origin
Brief history of geology * Catastrophism- (17th & 18th century)- earth shaped by sudden, huge disasters from unknown causes no longer in operation * Uniformitarianism- the physical, chemical, and biologic laws that operate today have operated through the geologic past.
The geologic record * Process comparison: slow versus rapid (grand canyon vs.
Geologic time * Relative dating: events are places in their proper sequence or order without knowing their specific age * Law of superposition: in a sequence of sedimentary rocks or lava rocks, the youngest layer is on top and the oldest layer is on the bottom. * Principle of fossil succession: fossil organisms succeed one another in a definite and determined order, and therefore any time period can be recognized by its fossil content * Radiometric dating: gives actual dates based on known rates of decay for radioactive isotopes
Geologic time scale * Eons, eras, periods, epochs * Years added after divisions * Precambrian 88% time
Scientific inquiry: the scientific method * 1. Start with observations * Hypothesis: a testable explanation, can be many to explain same phenomenon * Experiments to test hypothesis * Accept, modify, reject the hypothesis * Theory: well-tested hypothesis, widely-accepted view that the scientific community agrees best explains the observations
Earths spheres * Hydrosphere: all salt water and fresh water (above and below ground) * Atmosphere: thin envelop of gas around the earth, protects from heat and UV radiation * Biosphere: all life on earth * Geosphere: the solid earth, 6400 km from surface to center
Earth as a system * Components (spheres) interact in the Earth system * Closed system: movement of energy but no movement of matter in/our of system * Open system:
Early evolution of Earth * Nebular theory: bodies in the solar system evolved form enormous, rotating cloud (solar nebula) * 5 Ga: nebula contracts (gravity), rotates faster flat, disc with protosun
Earths internal structure:
The crust * 1. Oceanic: * 7 km, 5 mi * Basalt * Relatively homogenous * 2. Continental: * 35-40 km, 25 mi (to >70 km, 40 mi) * Many rock types * Average composition in granitic (granodioritic)
The mantle * 82% volume, solid, to 2900 km (1800 mi) * Change chemical composition (+Mg, +Fe) * Peridotite- dominant rock type in upper mantle * Upper mantle to 660 km ) 410 mi * Lithosphere: rigid outers shell, uppermost
