Evolution of Life and Earth (Historical Geology)

Physical vs. Historical Geology ► Physical Geology- Origin, classification, and composition of Earth materials and internal and surficial processes ► Historical Geology- Earth evolution, changes in lands and seas, mountain building and destruction, fossil succession through time, and history of the solar system

Scientific Method  Questions  Collection of Data  Development of Hypothesis  Testing of Hypothesis

The beginning ► The Big Bang  Most scientist believe that the universe was created in a single event known as the Big Bang ► This occurred ~15 billion years ago  Some studies suggest 22 bya  Our Solar System started to form about 5 bya

Our Solar System ► Solar Nebula Hypothesis  Cold, Rarified cloud of gas and dust particles  Dust cloud starts counterclockwise rotation around proto-sun  Eddies in dust cloud begin planetary development: cold homogeneous accretion

Final Phase of Formation ► Eventually, gravitational collapse at core of rotating disc forms the Sun  Solar wind drives out lighter elements  Leaving heavy elements in inner solar system and lighter elements in outer system

Earth ► Formative Interval  Hadean Eon: bya ► Accretion and Differentiation  Heating, partial melting and solid diffusion  Ni and Fe migration to core  Mantle separation forming lighter crust

Differentiation ► Source of Internal heat  Accretionary heat  Heat caused during bombardment  Radioactive decay ► Development of Magnetic Field  Caused by movement of liquid core

Crustal Develoment ► Crust formed by cooling magma ocean ► Komatitites formed early in Earth’s crust ► Continental Crust and Water present as early as 4.4 bya

Evolution of the Atmosphere and Hydrosphere ► Primitive atmosphere before 3.8bya

The Oceans ► Origin of Oceans (After 4.4bya)  Tied to the onset of the Hydrologic cycle  Salinity due to chemical weathering

Standard Geologic Time Scale ► Divisions of Time  Eons (largest): Hadean, Archean, Proterozoic, and Phanerozoic  Eras- units within eons: Eras within the Phanerozoic are the Paleozoic, the Mesozoic, and the Cenozoic.  Periods, Epochs and Ages: decreasing order subdivisions of geologic time

Understanding Earth’s Changes ► Catastrophism - Earth surface changes through large scale events ► Uniformitarianism  James Hutton ► Dynamic/Cyclic Concept of Earth History ► Used principle of actualism (uniformitarianism) ► Wrote first great Geology text ( Theory of the Earth)