Earth s s Geologic History

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Brianne Warren
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1 The Earth s s Geologic History and The Earth s s Interior Earth s s Geologic History Geologic timescale Divides Earth s s history into relative time periods Relative dating based on: (apply for entire universe) Principle of superposition (rock layers) Principle of cross-cutting cutting relationships (A A rock or fault is younger than any rock (or fault) through which it cuts.) Igneous intrusions, faults Fossils Provide information on geologic timescale Three basic ways fossils can be preserved: Original preservation preserved preserved actual organism Mineralization rocklike rocklike copy of the original Fossil impression impression in soft sediments Index fossils lived lived short time on Earth Radiometric Dating Antoine Henri Becquerel Discovered that uranium atoms undergo radioactive decay Form a new element --- lead Occurs at a specific rate called half-life life Use: Uranium 238 half half-life life 4.5 billion years Potassium 40 half half-life life 1.3 billion years Uranium 235 half half-life life 700 Carbon 14 half half-lifelife 5,730 years Used because all things living contained carbon Use The Geologic Timescale Used to represent history of Earth Largest period is called the eon Three eons make up Earth s s history: Archean Proterozoic Phanerozoic 1

The Archean Eon Began approximately 4.5 billion years Violent time in Earth s s history Bombardment by meteorites and asteroids Evidenced by surface of the Moon pubs.usgs.

5 billion years The Proterozoic Eon Archean Middle Early Oldest microfossils Geochemical evidence of oldest biological fixing carbon Oldest known rocks Time of origin of

5 billion years Period before 570 Included Archean and Proterozoic eons Known as Precambrian time Proterozoic ended 570 Entered the eon in which we live Called the

2 The Archean Eon Began approximately 4.5 billion years Violent time in Earth s s history Bombardment by meteorites and asteroids Evidenced by surface of the Moon pubs.usgs.gov updatecenter.britannica.com First life-forms forms Stromatolites colonies of single-celled cyanobacteria Late 3.0 to 2.5 billion years The Proterozoic Eon Archean Middle Early Oldest microfossils Geochemical evidence of oldest biological fixing carbon Oldest known rocks Time of origin of Earth 3.4 to 3.0 billion years 3.4 to 4.6 billion years 4.6 billion years Stromatolites Archean eon ended 2.5 billion years Period before 570 Included Archean and Proterozoic eons Known as Precambrian time Proterozoic ended 570 Entered the eon in which we live Called the Phanerozoic eon Proterozoic Late Middle Early Oldest multicellular life First appearance of sexually reproducing organisms 1.0 billion to to 1.0 billion years 2.5 to 1.7 billion years Edicaran fauna Soft-bodied organisms 2

The Phanerozoic Eon The Paleozoic Era Phanerozoic eon composed of three time periods: Called eras Based on the occurrence of mass extinctions Each era subdivided into specific periods Paleozoic

3 The Phanerozoic Eon The Paleozoic Era Phanerozoic eon composed of three time periods: Called eras Based on the occurrence of mass extinctions Each era subdivided into specific periods Paleozoic consists of six periods Six periods: Early began 570 Cambrian lasted 65 Ordovician lasted 67 Silurian lasted lasted 30 Devonian lasted 45 Carboniferous lasted 73 Permian lasted 45 The Phanerozoic Eon Permian 245 to 290 Extinction of many kinds of marine animals, including trilobite First mammal-like like reptiles Paleozoic Silurian Ordovician Cambrian 408 to to 505 Earliest insects Earliest land plants and animals Peak development of Eurypterids Earliest fish Algal reefs Burgess shale fauna Earliest chordates, diverse 505 to 570 trilobites Earliest trilobites Earliest marine animals with shells Invertebrates dominant mollusks become abundant Diverse coral and echinoderms Graptolites abundant Paleozoic Carbonifero us Devonian 290 to to 408 Earliest reptiles Extensive coal-forming forests Earliest amphibians, ammonoids, sharks Extinction of armored fish, other fish abundant 3

The Mesozoic Era Began approximately 245 Three periods: Triassic Period lasted 37 Jurassic Period lasted 62 Cretaceous Period lasted 81 Extinction of dinosaurs 65 www.windows.ucar.

Decline of brachiopods Diverse bony fishes Earliest birds Abundant dinosaurs and ammonoids Modern coral groups appear Earliest dinosaurs and mammals with abundant cycads and conifers The Cenozoic Era

4 The Mesozoic Era Began approximately 245 Three periods: Triassic Period lasted 37 Jurassic Period lasted 62 Cretaceous Period lasted 81 Extinction of dinosaurs 65 Mesozoic Cretaceous Jurassic Triassic 438 to to to 635 Extinction of dinosaurs and ammonoids Earliest placental mammals Climax of dinosaurs and ammonoids Earliest flowering plants Decline of brachiopods Diverse bony fishes Earliest birds Abundant dinosaurs and ammonoids Modern coral groups appear Earliest dinosaurs and mammals with abundant cycads and conifers The Cenozoic Era Mammals emerged as dominant life-form form Began 65 Divided into: Tertiary period appearance of grasses Lasted 63 Divided into periods called epochs Quaternary large large-scale glaciation facstaff.gpc.edu Quaterinary Present to 2 Humans, mastodons, mammoths The Earth s s Interior A Model Developed using seismic waves Cenozoic Tertiary: Neogene Paleogene 2 to 65 million years Large carnivores Abundant grazing mammals Earliest grasses Large running mammals Many modern groups of mammals Deepest drilling is 9 miles Deepest mine is slightly over 2 miles Model is constructed by inference -- can t t travel there! Earth is so large can t t be studied by direct observation! 4

Three major layers Core -- Mantle -- Crust Earth s s Interior 1 - The Core Outer liquid portion Inner solid portion Composition believed to be

extremely hot = 8,000 F Used seismic waves to reveal composition Impossible to observe directly because it is so hot and has extremely high

thick -- extremely high pressures Heat moves upward through mantle Forms convection cells Extreme heat comes from: Radioactive decay Friction

mantle called the asthenosphere Flows like thick syrup Top layer - 100 to 200 kilometers below surface.

5 Three major layers Core -- Mantle -- Crust Earth s s Interior 1 - The Core Outer liquid portion Inner solid portion Composition believed to be iron and nickel 2900 kilometers thick 83% of the Earth's volume It is solid 1,800 miles to outer core 1,300 miles to inner core Core is extremely hot = 8,000 F Used seismic waves to reveal composition Impossible to observe directly because it is so hot and has extremely high pressure 2 - The Mantle Most of Earth s volume Composed of a hot solid material Silicon, oxygen, iron, aluminum, and magnesium 1,800 miles thick -- extremely high pressures Heat moves upward through mantle Forms convection cells Extreme heat comes from: Radioactive decay Friction Residual heat All are left over from Earth s s formation Earth s s crust floats on top of upper mantle (Like a cracker floating on soup) Upper mantle called the asthenosphere Flows like thick syrup Top layer to 200 kilometers below surface. Physical properties are different from the rest of the upper mantle -- rocks in this upper portion of the mantle are more rigid and brittle because of cooler temperatures and lower pressures. 5

3 - Crust Seven elements make up 99% of crust

iron, calcium, magnesium, sodium form remainder

Oceanic crust made of basalt Lithosphere Solid

6 3 - Crust Seven elements make up 99% of crust Oxygen and silicon = 72% of the crust Aluminum, iron, calcium, magnesium, sodium form remainder Outer portion composed of solid rock Thickness from 40 miles to 3 miles 40 miles under mountains 3 miles under parts of the ocean Oceanic crust made of basalt Lithosphere Solid outer crust of Earth Rock and hot plastic-like like upper mantle 6

EARTH S HISTORY. What is Geology? logy: science. Geology is the scientific study of the Earth, including its:

EARTH S HISTORY. What is Geology? logy: science. Geology is the scientific study of the Earth, including its: EARTH S HISTORY 1 What is Geology? Geo: earth logy: science Geology is the scientific study of the Earth, including its: composition, structure, and physical properties. 2 1 Geologists study: the origin