* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The History of the Earth
Survey
Document related concepts
Geomorphology wikipedia , lookup
Post-glacial rebound wikipedia , lookup
Spherical Earth wikipedia , lookup
Composition of Mars wikipedia , lookup
History of geomagnetism wikipedia , lookup
Anoxic event wikipedia , lookup
Tectonic–climatic interaction wikipedia , lookup
Geochemistry wikipedia , lookup
History of Earth wikipedia , lookup
Algoman orogeny wikipedia , lookup
History of geology wikipedia , lookup
Age of the Earth wikipedia , lookup
Large igneous province wikipedia , lookup
Transcript
The History of the Earth Geologic time • Planet Earth is approximately 4.5 X 109 years old (4.5 billion years or 4,500 million years) –Rocks of the crust provide clues to Earth’s past • By analyzing these clues we can infer events from the past • Principle of Uniformitarianism –Major assumption in geology –Events in the past occurred the same way that they are occurring today. Examples Include: • Weathering/erosion • Deposition • Volcanism • Plate tectonics James Hutton (1726-1797) • First to interpret sequence of events in an unconformity • Published “Theory of the Earth” in 1785 • He was the one who recognized the uniform natural laws that govern geologic processes “uniformitarianism” Geologic Time • Geologists have divided Earth’s history into time units based on the the fossil record Geologic Time • A study of the fossil record shows –A great variety of plants, animals, and simpler life forms have lived on Earth in the past –That life forms have evolved through time –Most life forms of the geologic past have become extinct A Brief History of the Earth • Eon – largest segment of geologic time –Era • Period –Epoch – smallest segment of geologic time Let’s compress Earth’s 4.5 billion year history into 1 year • January 1 – origin of earth • Feb. 26 – earliest earth rocks formed • March 23 – first of simple life forms as simple bacteria in the sea and photosynthesis • July 22 – oxygen begins to accumulate in atmosphere • Sept. 1 – first green algae and organisms w/ a nucleus • November 17 – the proliferation of life; beginning of • November 21 – the first fish; the first vertebrate • November 27 – the first life on land, plants • December 2 – amphibians move to land • December 13 – the first mammals • December 14 – 26 – age of dinos December 31st at 11:49 p.m. • Humans emerge • Within last minute – all recorded human history • 2 seconds before midnight – Declaration of Independence • 1 second before midnight – start of Industrial Revolution Geologic Time Activity: May 11, 2017 • Get into groups of 2 • Obtain a worksheet from the front of the classroom and follow instructions on creating your own geologic timeline • Markers, colored pencils, scissors, receipt paper, are all available for you to utilize RELATIVE TIME VS. ABSOLUTE TIME PLACES EVENTS IN A IDENTIFIES THE SEQUENCE BUT DOES ACTUAL DATES OF NOT IDENTIFY THEIR GEOLOGIC EVENTS ACTUAL DATE OF OCCURRENCE EXAMPLE A LIST IN THE EXACT TIMES AT CHRONOLOGICAL WHICH YOU DID THESE ORDER OF WHAT YOU THINGS HAVE DONE TODAY UP UNTIL THIS TIME • Law of Superposition in undisturbed sedimentary rocks, the oldest rock layers are at the bottom and the youngest are at the top Grand Canyon Law of Superposition • Rock layers are older than folds found in them – Layers were there before they were folded Principle of Original Horizontality • Sediments are deposited in flat layers (horizontal) • Most sedimentary rocks occur in the form of layers called beds or strata • These layers are the result of sediment deposition during a natural event such as a storm or flood Law of Cross-Cutting Relationships • An igneous intrusion is younger than the rock it has intruded into The fault is younger than the rock it cuts Igneous Intrusion – Cross Cutting Principle of Inclusions The inclusions are older than the rocks which contain them https://www.youtube.com/watch?v=bD5RylDR3 CU Unconformity • When a new rock layer is formed atop an eroded surface • https://www.youtube.com/watch?v=lMfPSdrrj ZI Place the following events in order starting with the oldest Principle of Faunal Succession • Fossils occur in a consistent vertical order in sedimentary rocks all over the world • This principle doesn’t depend on any preexisting ideas of evolution • Geologists interpret fossil succession to be the result of evolution – the natural appearance/disappearance of species through time Absolute Dating • Radiometric Dating • Naturally-occurring radioactive materials break down into other materials at known rates. This is known as radioactive decay. • Radioactive parent elements decay to stable daughter elements. • Many radioactive elements can be used as geologic clocks. Each radioactive element decays at its own nearly constant rate. Once this rate is known, geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements. – How does carbon-14 dating work? • The half-life is so short (5730 years) that this method can only be used on materials less than 70,000 years old. Archaeological dating uses this method. • Also useful for dating the Pleistocene Epoch (Ice Ages). The Standard Geologic Time Scale • The geologic time scale has been determined bit-by-bit over the years through relative dating, correlation, examination of fossils, and radiometric dating. • Geochronologic units or time units • Eon = Largest division of time scale. In order from oldest to youngest, the eons are: – Hadean Eon (early Earth still molten - hot as hades - no rock record) - beginning about 4.6 billion years ago – Archean Eon - "ancient or archaic" - oldest rocks on Earth – Proterozoic Eon - "beginning life" (2.5 billion to 544 million years ago) – Phanerozoic Eon - "visible life" (544 million years ago to present) • The Archean and Proterozoic are collectively referred to as the Precambrian (meaning "before the Cambrian Period"). • Era = A major division of geologic time, divisible into geologic periods. The Phanerozoic Eon is divided into three eras. From oldest to youngest, the eras are: – Paleozoic Era- "ancient life" (trilobites) – Mesozoic Era - "middle life" (dinosaurs) – Cenozoic Era - "recent life" (diverse mammals) • Eras are divided into periods. Periods can be divided into epochs. - Epochs can be divided into ages. • Earthquakes are vibrations of Earth produced by the rapid release of energy from rocks that rupture because they have been subjected to stresses beyond their limit. • This energy, which takes the form of waves, radiates in all directions from the earthquake's source, called the focus. The movements that produce most earthquakes occur along large fractures, called faults, that are associated with plate boundaries. • Two main groups of seismic waves are generated during an earthquake: • (1) surface waves, which travel along the outer layer of Earth • (2) body waves, which travel through Earth's interior. Body waves are further divided into primary, or P, waves, which push (compress) and pull (expand) rocks in the direction the wave is traveling, and secondary, or S, waves, which shake the particles in rock at right angles to their direction of travel. P waves can travel through solids, liquids, and gases. Fluids (gases and liquids) will not transmit S waves. In any solid material, P waves travel about 1.7 times faster than do S waves. • http://ocean.si.edu/oceanvideos/demonstrating-earthquakes-seismicwaves • https://www.youtube.com/watch?v=3lie1Myu XfQ • The location on Earth’s surface directly above the focus of an earthquake is the epicenter • An epicenter is determined using the difference in velocities of P and S waves • There is a close correlation between earthquake epicenters and plate boundaries • The principal earthquake epicenter zones are along the outer margin of the Pacific Ocean, known as the circum-Pacific belt and through the world’s oceans along the oceanic ridge system • Seismologists use 2 fundamentally different measures to describe the size of an earthquake – intensity and magnitude • Intensity – measure of the degree of ground shaking at a given locale based on the amount of damage • The modified mercalli intensity scale uses damage to buildings in California to estimate the intensity of ground shaking for a local earthquake • Magnitude – calculated from seismic records. Estimates the amount of energy released at the source of an earthquake • Using the Richter Scale, the magnitude of an earthquake is estimated by measuring the amplitude of the largest seismic wave recorded • Logarithmic scale expresses magnitude (10fold increase in ground shaking corresponds to an increase of 1 on the richter scale) 4 Major Zones of Earth’s Interior • 1. Crust – very thin outer layer • 2. Mantle – rocky layer below crust (2885 km thick) • 3. Outer core – characteristics of a mobile liquid (2270 km thick) • 4. Inner core – solid metallic sphere with a radius of 1216 km • Continental crust – made mostly of granitic rocks • Oceanic crust – basaltic composition • Mantle – made up of ultramafic rocks such as peridotite • Core – iron and nickel • Lithosphere – crust and uppermost mantle which form Earth’s cool rigid outer shell • Asthenosphere – beneath lithosphere; a soft relatively weak layer • Among the most basic geologic structures associated with rock deformation are folds – These are flat-lying sedimentary and volcanic rocks bent into a series of wavelike undulations – Anticlines – formed by upfolding or arching of rock layers – Synclines – downfolds – Most folds are a result of horizontal compressional stresses Anticlines • Folds in which the oldest rock lies in the center or core and synclines have the youngest rock in its center core Faults • Faults are fractures in the crust along which appreciable displacement has occurred • Dip-slip faults – faults in which the movement is primarily vertical – Normal – Reverse Normal Fault • Dip-slip fault • The block above the fault has moved downward relative to the block below • Occurs in response to extension – usually in the Western U.S. Basin and Range Province and along oceanic ridge systems Thrust Faults • Low-angle reverse faults • Upper block above the fault plane moves up and over the lower block • Common in areas of compression such as regions where one plate is subducted under another (Japan) Strike-Slip Faults • Exhibit mainly horizontal displacement parallel to the fault surface Plate Tectonics • Continental Drift Theory – In the early 1900s Alfred Wegener set forth his continental drift hypothesis • A supercontinent called Pangaea began breaking apart into smaller continents about 200 mya and then the smaller continental fragments “drifted” to their present positions • To support the claim that the now-separate continents were once joined, Wegener and others used the fit of S. America and Africa, the distribution of ancient climates, fossil evidence, and rock structures • One of the main objections to the continental drift theory was the inability of its supporters to provide an acceptable mechanism for the movement of continents Plate Tectonics • Far more encompassing than continental drift • Says that Earth’s rigid outer shell (lithosphere) consists of 7 large and numerous smaller segments called plates that are in motion relative to each other • Most of Earth’s seismic activity, volcanism, and mountain building occur along the dynamic margins of these plates • A major departure of the plate tectonics theory from the continental drift hypothesis is that large plates contain both continental and oceanic crust and the entire plate moves – In contrast, in continental drift, Wegener proposed that the sturdier continents “drifted” by breaking through the oceanic crust, much like ice breakers cut through ice Boundaries • Divergent plate boundaries occur where plates move apart, resulting in upwelling of material from the mantle to create a new seafloor – Most occur along the axis of the oceanic ridge system and are associated with seafloor spreading, which occurs as rates between about 2 and 15 cm per year https://pubs.usgs.gov/gip/dynamic/topomap.html • New divergent boundaries may form within a continent (for example the East African rift valleys) where they may fragment a landmass and develop a new ocean basin • http://pubs.usgs.gov/gip/dynamic/East_Africa .html Convergent Plate Boundaries • Occur where plates move together, resulting in the subduction of oceanic lithosphere into the mantle along a deep oceanic trench – Convergence between an oceanic and continental block results in subduction of the oceanic slab and the formation of a continental volcanic arc such as the Andes of South America http://www.geographicguide.net/earth/pictures/an des.jpg Oceanic-Oceanic Convergence • Results in an arc-shaped chain of volcanic islands called a volcanic island arc • http://www.johnpratt.com/items/docs/Ids/m eridian/2005/images/aleutian.jpg • http://www.earthweek.com/2008/ew081128/ ew081128xLARGE.jpg • When 2 plates carrying continental crust converge, both plates are too buoyant to be subducted. The result is a “collision” resulting in the formation of a mountain belt such as the Himalayas • http://www.eduspace.esa.int/casestudy/imag es/subhim_meris_t2.jpg Transform Plate Boundaries • Occur where plates grind past each other without the production or destruction of lithosphere – Most transform faults join 2 segments of an oceanic ridge. Others connect spreading centers to subduction zones and thus facilitate the transport of oceanic crust created at a ridge crest to its site of destruction, at a deep ocean trench. Others, like the San Andreas Fault, cut through continental crust – http://www.geo.cornell.edu/geology/classes/geol 326/images/sanandreas.gif Plate Tectonics Support: • 1. Paleomagnetism – direction/intensity of Earth’s magnetism in the geologic past • 2. Global distribution of earthquakes and their close association with plate boundaries • 3. Ages of sediments from the floors of deep ocean basins • 4. Existence of island groups that formed over hot spots and provide a frame of reference for tracing the direction of plate motion • http://www.worldofstock.com/slides/SES1016 .jpg Mantle Convection • Slab-pull – cold, dense oceanic lithosphere is subducted and pulls the trailing lithosphere along • Ridge-push – gravity sets the elevated slabs astride oceanic ridges in motion. Hot buoyant plumes are considered the upward flowing arms of mantle convection Ridge-Push • One model suggests that mantle convection occurs in 2 layers separated at a depth of 660km • Another model proposes whole-mantle convection that stirs the entire 2900-km thick rocky mantle • Another suggests that the bottom third of the mantle gradually bulges upward in some areas and sinks in others w/o appreciable mixing Volcanoes