EARTH’S COMPONENTS & CHARACTERISTICS UNIT 9 Environmental Geology APES

GEOLOGIC TIME SCALE Organizes Earth’s 4.6 billion years of history into subgroups Subgroups: Eons Eras Periods Epochs 4 Major Eons…

1. Hadean Eon Oldest amount of time 4.6-3.8 billion years ago No rocks from this eon found on Earth Evidence from meteorites & moon rocks

2. Archean Eon 3.8-2.5 billion years ago Oldest rocks on Earth from this eon.

3. Proterozoic Eon 2.5 billion – 543 million years ago. First life forms appeared

4. Phanerozoic Eon 543 million years- present Paleozoic Era Diverse land plants, amphibians, reptiles, insects Mass extinction due to glaciation (global cooling)- killed 90% of species Mesozoic Era 248-66 million years Age of Reptiles Mass extinction due to climate change- 10-15% extinct Cenozoic Era 65 million years to present Age of Mammals

STRUCTURE OF THE EARTH Planetary differentiation- as more dense materials sank to center of earth, less dense material rose to surface

Layers of Earth Core- center, mostly iron Inner core- 1220 km thick, T & P cause iron to solidify Outer core- 3480 km thick, liquid iron, creates magnetic field Mantle- 70% of earth’s interior, made of O, Si, Mg Asthenospere- closest to core, gelatinous, where magma is formed Upper mantle- cooler, more solid, brittle Crust- outermost layer Crust + upper mantle make up lithosphere

Plate Tectonics Tectonic plates- made of… Uppermost mantle Crust- 2 types: Oceanic- thin (5-10 km), dense, rich in Fe, Mg, Si, below sea level Continental- thick (20-70 km), less dense, rich in Ca, Na, K, Al Constantly moving about 1-10 cm/year 15 major plates- We are on North American Plate

Plate Boundaries Where 2 plates meet 3 types of plate boundaries

1. Transform Boundaries Plates slide past each other at transform faults Movement is horizontal (strike-slip fault) To the left- sinistral To the right- dextral Mostly smooth movement If stuck, pressure builds, causes earthquakes

2. Convergent Boundaries 2 plates move toward each other 3 types:

a. OCEANIC - CONTINENTAL Oceanic plate is forced under continental plate Called subduction Creates deep-sea trench Creates volcanic mountains along continental plate. EX: Peru-Chile Trench and Andes Mountains of South America

b. OCEANIC - OCEANIC Oceanic plate is forced under another oceanic plate Called subduction Crust melts into mantle Creates deep-sea trench Creates arc of volcanic islands that parallel trench EX: Mariana Trench & Mariana Islands Aleutian Trench & Aleutian Islands

c.CONTINENTAL - CONTINENTAL Two continental plates collide Mountain ranges are created EX: Himalayas- Indian plate forced under Eurasian plate

3. Divergent Boundaries 2 plates move apart Creates rifts Magma comes to surface & cools, creating crust Usually in oceans, but can occur in continents (Africa’s Rift Valley) Creates mid-ocean ridges EX: Mid-Atlantic Ridge created when N.American plate pulls away from Eurasian plate.

CAUSES OF PLATE MOVEMENT Convection currents Hot mantle rises Cools down Cooled-down mantle sinks Creates currents that move plates.

THEORY OF CONTINENTAL DRIFT Alfred Wegner was first to propose theory of continental drift He said: All continents joined in large land mass called Pangea (Greek for “all land”) Pangea began breaking up 200 million years ago. Continents ended up where they are now Continents are still moving

Evidence of Continental Drift Fossils- similar plants & animals on widely separated continents Rock Formations- similar rock types & stratification between 2 continents Climate- Antarctica has coal deposits, indicating it had swamps, thus warmer weather= closer to equator

Geologic Hazards associated with Continental Drift Earthquakes Volcanoes Landslides Floods

Earthquakes Epicenter- point where first movement occurs Damage depends on soil underneath Modern contractors build weak spots, pads/floats to absorb vibration Underwater earthquakes cause tsunamis Destroy coastal ecosystems Saltwater infiltrates soil sewage/industrial waste infect freshwater supplies

Volcanoes Good Bad Created land (fertile soil), atmosphere, oceans Release sulfur, combines with H20 to form sulfuric acid; interferes with solar radiation, cools climate (Mt. Pinatubo- Philippines) Dust/Ash- can change climate by blocking sunlight (1815- Mt. Tambora in Indonesia, snowed in July in parts of New England, “year without a summer”) Clouds of hot, toxic gases Mudslides

Landslides Mass wasting/movement Usually slow & subtle, can happen all at once Construction, forest clearing, agriculture, building on steep slopes increase frequency & damage

Flooding Excess water that overflows stream banks Contaminates everything- very costly Pavement/buildings- speeds rate of runoff, soil has no chance to absorb Floodplains- fertile, attract people/agriculture, affected most by flooding READ chapter 16 on Natural Disasters!!