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Earth Science November 12, 2005 Dr. Clodfelter The Geologic Time Scale The history of the Earth is broken up into a hierarchical set of divisions for describing geologic time The Geologic Time Scale, cont. Highlights of recent fossil finds from throughout geologic time (from most ancient to most recent) are: • Precambrian Era: the first fossil bacteria, sponges, corals, and algae appear • Cambrian Period: abundant invertebrate fossils such as mollusks, crustaceans The Geologic Time Scale, cont. • Triassic Period: the first fossils of primitive dinosaurs appear • Jurassic Period: the first fossil mammals and birds; first fossil flowering plants appear • Cretaceous Period: large fossil dinosaurs appear Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Precambrian Precambrian Eon 4.5 Billion to 543 Million Years Ago • Nearly 4 thousand million years after the Earth began • The first animals left their traces • Makes up roughly 7/8 of the Earth's history Archaean Era 3.8 to 2.5 Billion Years Ago • The atmosphere was very different from what we breathe today • The Earth's crust cooled enough that rocks and continental plates began to form • Life first appeared on Earth – bacteria microfossils Phanerozoic Eon 543 Million to • Majority of macroscopic organisms, fungal, plant and animals lived • Appearance of animals that evolved external skeletons – like shells – and animals that formed internal skeletons – like vertebrates Paleozoic Era 543 to 248 Million Years Ago • In the beginning, multicelled animals underwent a dramatic "explosion" in diversity • At the end, the largest mass extinction in history wiped out approximately 90% of all marine animal species Paleozoic Era 543 to 248 Million Years Ago Mesozoic Era 248 to 65 Million Years Ago • • • • • Mesozoic means "middle animals” Lasted 70 Million Years Time of transition The world-continent of Pangaea existed The time in which life as it now exists on Earth came together • Important today because of the fossils and oil left behind Mesozoic Era 248 to 65 Million Years Ago Divided into three time periods: – the Triassic (245208 Million Years Ago) – the Jurassic (208146 Million Years Ago) – the Cretaceous (146-65 Million Years Ago) Dinosaurs in the Mesozoic Era Dinosaurs... – Evolved in the Triassic Period – Became more diversified in the Jurassic Period – Became extinct in the late Cretaceous Period – Fossils of some of the last dinosaurs to walk the Earth can be found in Montana The Cretaceous/Tertiary Boundary in Montana Cenozoic Era • The most recent of the three major subdivisions of animal history – The other two are the Paleozoic and the Mesozoic • Spans only about 65 million years • Sometimes called the “Age of Mammals” A Continental Jigsaw Puzzle: Putting the Pieces Together • • • • 1911 German meteorologist Alfred Wegener theorized that about 300 million years ago all the continents we know today were joined together in a single continent • he named it “Pangaea” (pronounced Pan JEE uh) A Continental Jigsaw Puzzle: Putting the Pieces Together, cont. • Wegener suggested that Pangaea split apart and its pieces began to “drift,” or move away from each other • He put together his own evidence, as well as others’, to support his Theory of Continental Drift A Continental Jigsaw Puzzle: Putting the Pieces Together, cont. • At first, Wegener’s ideas were very popular because his evidence seemed quite convincing • Yet a number of observations still remained unexplained – What forces caused the continents to move? • Due to these remaining problems, Wegener’s theory rapidly lost support and continental drift became “just another theory” What are Crustal Plates? • Earth’s crust isn’t one continuous surface like the skin of an orange • It is made up of gigantic pieces, like pieces of a jigsaw puzzle • Each piece is called a crustal plate • Some plates form the floor of the oceans while other carry the continents Crustal Plates • Molten rock around the Earth’s core heats up the mantle above • Currents of molten rock rise up through the mantle like boiling water • As each current hits the underneath of the crustal plates, it starts to spread out • This slowly pushes or tears the crust apart Crustal Plates • The plates are always on the move • There are three basic types of plate boundaries – where they are sliding past each other – where plates are separating – where they are converging (approaching each other) Crustal Plates • Spreading Center - the boundary between separating plates – Usually found in mid-ocean and are marked by rugged mountain chains called mid-ocean ridges • As plates move apart a gap continuously opens between them • Molten rock from the earth’s interior flows into this gap – New crust is continuously formed Plates and Sea Floor Spreading Crustal Plates • When plates collide, the force can fold and thrust upward to form mountains • Or the force can push the ocean floor downward to form a deep valley called a trench • Here, molten rock can break through the seabed to form chains of islands like the Hawaiian Islands The Mariana Trench The San Andreas Fault Crustal Plate Activity Crustal plate activity can… • Cause earthquakes, volcanic activity, and tsunamis • Earthquakes are signs of the great stresses and which affect the Earth’s crust • Over a million earthquakes occur every year • Tsunamis are giant tidal waves and can travel at 500 mph! • Dinosaur Fossil bones have been found in many different parts of the world – Further supports Wegener’s single continent theory • The dinosaurs disappeared suddenly – Different theories as to why – Most widely accepted is the Big Bang Theory • Scientists theorize that a meteor hit the Earth at nearly the speed of light (186,000 miles per second!) • Caused a total black out of the sun • This meteor is believed to have caused the Gulf of Mexico Gulf of Mexico • The Earth weighs about 6000 million million million tons • Two-thirds of the earth is covered by water • It would take more than 250 days to walk around the equator • Every year, North America and Europe separate by 3/4ths of an inch • Scientists predict that life on Earth will only last 50 million more years Earth = Onion • Crust – outermost layer, solid rock, but very thin like skin • Mantle – denser and heavier than the crust, inner part of the mantle is described as “plastic” because it is semi-liquid rock • Core – outer part is made of molten liquid rock that is very dense and heavy, “core” of the core becomes solid and even more dense • Forms when rocks deep under the Earth’s crust melt • Heat from friction as the rocks rub together can also form magma • In places where the Earth’s crust is weak, magma wells up on the surface as volcanoes or lava flows • As it cools, it becomes solid forming new rock • Igneous Rock – formed form cooled magma • Sedimentary Rock – formed by the combining together of broken bits of other rocks or sediments • Metamorphic Rock – changed by extreme pressure or heat • Contain complex chemicals called minerals • Kinds of Minerals + Size of Crystals = how the rock was Formed • Small crystals = rapid cooling • Large crystals = more lengthy cooling Ring of Fire Mount St. Helen Krakatoa, Indonesia • Volcanic eruption was heard 3,000 miles away • Caused great tidal wave that killed perhaps 36,000 people • Crystals from the magma are smaller because they cooled quickly Crater Lake, Oregon • The caldera has filled creating one of the deepest lakes • It may erupt again • Made by the action of water and wind as they laid down like layers of a cake • Pressure increases and they are warmed by the heat from deep in the Earth • Sediment becomes a solid mass of rock Arbuckle Mountains Sandstone Limestone Decaying Plant Material Peat Coal • Sea Creature dies and sinks to the sea bed • The soft body slowly decays creating oil with a layer of gas sitting on top • Skeleton is covered in layers of mud which gradually become solid rock • Sea bed rises above sea level • Erosion moves rock covering fossils so they are now exposed on land • Radio-active carbon found in all living things • Begins to break down after an animal or plant dies • By measuring the amount of Carbon – 14 in a fossil, scientists can tell how old it is • This is called Carbon Dating • Layer of air surrounding the Earth • Consists of different kinds and amounts of gases – Nitrogen, Oxygen, Carbon Dioxide • Protects the Earth’s surface – Filters out harmful radiation from the sun – Insulates Earth and stops the sun’s heat from escaping back into space Three Main Layers 1) Ionosphere • • • Extends about 50 miles above the surface Rarified air Temperature gradually rises as you move away from the Earth 2) Stratosphere • Extends about 30 miles above the Earth’s surface • Contains very little air or water vapor • Colder than Ionosphere, but warmer than the Troposphere 3) • • • • Troposphere Bottom layer About 10 miles thick Contains nearly all the atmosphere’s air, water vapor, and clouds Temperature gradually drops until is reaches the stratosphere • Warm air… – Lighter and less dense than cold air – Rises up into the atmosphere – Produces low pressure • Cold air… – Presses down heavily on the Earth’s surface – Produces high pressure Cirrus – Thin, curly, and wispy shapes – Formed in the upper Troposphere – Contain ice crystals Cumulus – Heaped clusters like loose cotton balls – Have flat bases and dome shaped tops – Sometimes build up into thunder clouds Stratus – Formed when Cumulus clouds group together to form a continuous layer – Grayer in color than Cumulus – Bottom of the Stratus layer is in the lower Troposphere A Meteorologist Measures… • • • • • • • Air pressure Temperature Humidity Winds speeds and directions Precipitation (rain, hail, snow, sleet, fog) Cloud types and their heights Visibility – Name used in Asia – Like a tornado and hurricane combined – Rapidly rotating tunnel of air – Moves over land – Can be 300 miles in diameter – Winds speed at more than 125 mph • Similar to cyclones, but much smaller • Sometimes only a mile or so across The name given to a cyclone which develops in the western Atlantic Ocean Infancy Youth Maturity Old Age Alps Rocky Mountains Arbuckle Mountains Cumberland Mountains Yellowstone River Colorado River Rio Grande Red River