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Unit V: Earth's History

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Unit V: Earth's History Rock Outcrop on Rte. 12 Depauville Unit V: Earth’s History Review Book pp.97-112. Original photo taken by Mr. O on 8/11/10. Objective #1 • Describe processes that formed the atmosphere and oceans of early Earth. Objective #2 •Explain the difference between relative and absolute age. • Evidence suggests that the atmosphere and oceans of the early Earth began to form from gases emitted by volcanic eruptions from the Earth’s interior through a process called outgassing. • Outgassing was thought to add the gases water vapor (H2O), carbon dioxide (CO2) and nitrogen (N2). Image taken from http://www.globalchange.umich.edu/gctext/Inquiries/Inquiries_by_Unit/Unit_8_files/image011.jpg on 8/9/10. Image taken from http://www.fossilmuseum.net/Tree_of_Life/Stromatolites.htm on 8/11/10. • The Earth’s hot surface was cooled by precipitation that fell over millions of years and formed the oceans. • Sedimentary rocks of marine origin dating back approximately 4 billion years provide evidence for the presence of an early ocean. • What percent of today’s atmosphere is oxygen? • 21% (ESRT p.1) •If outgassing/volcanic eruptions did not add oxygen to the atmosphere and oceans, how do scientists think it got there? •Photosynthesis from algae and simple Image taken from producers in the ocean. http://www.scitizen.com/cacheDirectory/HTMLcontributions/img/algae20 100408.jpg on 8/11/10. Image taken from McGuire, Thomas. Earth Science: The Physical Setting. New York: Amsco, 2005. Relative Age • Concerned with sequence of events that have occurred, comparing the ages of objects. • Relative age is not concerned with actual age. • Example: Rock Layers along Rte. 12 Image taken from http://academic.brooklyn.cuny.edu/geology/leves Clayton near Spicer’s Bay on/core/topics/time/graphics/bracketing.gif on 8/11/10. Original photo taken by Mr. O on 8/11/10. Absolute Age • Actual age • The most accurate method of determining the absolute age of geologic events and rock is by radioactive dating. Image taken from http://en.wikipedia.org/wiki/Radiometric_dating on 8/11/10. Objective #3 • In a section of rock, determine order of geologic events by using chronology of layers, intrusions/extrusions, faults, folds, joints, unconformities and internal characteristics. Principle of Superposition • Idea that the oldest rock layers in a series of horizontal sedimentary rock are found at the bottom. Image taken from http://www.astrofoto.ca/stuartheggie/Grand_Canyon/Grand_Canyon_23.jpg on 8/11/10. • What type of geologic events cause the principle of superposition to not remain true? • Faulting • Folding • Overturning of rocks Image taken from http://geomaps.wr.usgs.gov/socal/geology/inland_empire/images/san_andreas_fault.jpg on 8/11/10. Image taken from http://www.nps.gov/history/history/online_books/geology/publications/state/tx/1968-7/images/fig26.jpg on 8/11/10. Image taken from Image taken from http://www.gangiteach.com/practice%20tests/geohist6.gif on http://www.indiana.edu/~geol105/images/gaia_chapter_5/dike&sill.jpg on 8/11/10. 8/11/10. • The rock layers through which igneous intrusions or extrusions cut are older than the intrusions or extrusions themselves, since the rock layers must be formed prior to the intrusion of magma or extrusion of lava. Contact Metamorphism • Process of rock changing due to contact (being touched) with hot magma or lava. Image taken from http://www.nvcc.edu/home/cbentley/geoblog/2009_10_01_archive.html on 8/11/10. Contact metamorphism is younger than the rock layers that were metamorphosed. • Faults – Cracks in rock along which movement has occurred. • Joints Image taken from http://www.geology.wisc.edu/courses/g112/Images/salv_faults.jpgon 8/11/10. – Immovable cracks • Folds – Bends in the rock strata. Image taken from http://farm3.static.flickr.com/2327/2212321452_7dec0280d0.jpg on 8/11/10. Folding and faulting associated with the San Andreas fault, along highway 14 near • Faults, joints Palmdale, California. and folds are younger than the rocks in which they appear. Image taken from http://strike-slip.geol.ucsb.edu/KESSEL/palmdaleroadcut.html on 8/11/10. •These distortions in rock occur due to changes in temperature and pressure. Image taken from http://www.gangiteach.com/practice%20tests/geohist4.gif on 8/11/10. Practice Diagram #1 Image taken from Practice Diagram #2 Image taken from • Fragments that occur inside a rock are older than the rocks in which they are found, since they were already around before the rock was made. Image taken from http://www.answersincreation.org/curri Image taken from culum/geology/images/conglomerate.j http://www.babble.com/CS/blogs/strollerderby/2009/06/chocolate_chip_cookie.jpg pg on 8/11/10. on 8/11/10. Quartz vein in quartzite(metamorphosed sandstone) rock in Killarney, Ontario ESRTp.7 Image taken from http://www.flickr.com/photos/31856336@N03/galleries/72157623975198 336/ on 7/19/10. • However, cracks and veins are younger than the rocks in which they occur. • Veins- – Mineral deposit that have filled a rock crack or permeable zone • Sedimentary rocks are younger than the sediments and the cements that formed them. Image taken from http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/Inform ationCirculars/IC1987-05/Pages/key.aspx on 8/11/10. Unconformity • A “gap” in the geologic rock record due to erosion or nondeposition. • An unconformity indicates that a portion of the rock record is missing. Image taken from http://lams.slcusd.org/pages/teachers/saxby/wordpress/wp-content/uploads/2010/03/syncline_unconformity.jpg on 8/11/10. #1___________________________________________ #2___________________________________________ #3___________________________________________ #4___________________________________________ Image taken from http://stevekluge.com/geoscience/images/unconformity1.jpg on 8/11/10. PreCambrian-Cambrian Unconformity (Rte. 12 Alex Bay near Schemerhorn Landing) Original photo from Mr.O taken on 8/11/10. Close up of Unconformity near Schemerhorn Objective #4 • Explain how rocks and geologic events in one place can be matched to another by using correlation of rock layers, fossils and volcanic ash. Objective #5 Identify two characteristics of a good index fossil. The determination of the relative age of rock in geologic history can be accomplished through the use of correlation techniques. Correlation • Process of determining that rock layers or geologic events in two separate areas are the same. Correlation involves observing similarity and continuity of rock layers in different locations, comparing fossil evidence and using volcanic time markers. Images taken from http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/froshlec8.html on 8/12/10. Outcrop at Aqua Zoo in Alex Bay • Outcrop- • Bedrock exposed at earth’s surface. • Scientists can make observations about an area and the landscape by “walking the outcrop”. Original Photo taken by Mr. O on 8/11/10. Rock Outcrops Rte.12 Depauville • An example is matching up sedimentary rock strata on opposite sides of a valley. • Rocks can be matched on the basis of similarities in appearance, color and composition. Original photo taken by Mr. O 8/11/10. Correlation of Rock Layers between Three National Parks Image taken from http://www.fas.org/irp/imint/docs/rst/Sect2/correlation.jpg on 8/12/10. Fossils Remains or traces of once living organisms found in sedimentary rock. Amphibian tracks from Oklahoma about 300 million years old that show it was raining at time of preservation Image taken from http://www.flickr.com/photos/31856336@N03/galleries/72157623975198336/#photo_236128744 on 8/11/10. B A Outcrop @ 6th Hole C-Way Golf Course 8/11/10. on O Mr. by taken photo Original • Fossils found in rocks at lower levels are considered to be older than fossils found in rocks at higher levels. • Presence of marine fossils indicates that the rock was formed in the sea and can be inferred that the area was submerged at some time during geologic history. Original photo taken by Mr. O on 8/27/10. Index or Guide Fossils • Fossil characteristics of a certain geologic time used to correlate rock layers. Image taken from http://www.geology.ohio-state.edu/~vonfrese/gs100/lect29/xfig29_04.jpg on 8/12/10. • Index fossils are used because of widespread horizontal distribution (geographical) in sedimentary rocks and their relatively short period of existence on Earth (narrow vertical distribution). ESRT p.8&9 Image taken from http://www.cartage.org.lb /en/themes/Sciences/Ear thscience/Geology/About Geology/GeologicTime/I ndexFossils/fossils.gif on 8/12/10. Volcanic Time Markers • A volcanic eruption is relatively short in duration when compared to the many years necessary to form sedimentary rock or build up the Earth’s surface. • When a volcano erupts, a layer of volcanic ash is rapidly deposited over a large area. Image taken fromhttp://regentsearth.com/Graphics/Thumbs.htm on 8/12/10. Volcanic Ash Image taken from http://geology.com/articles/volcanic- Image taken from ash/volcanic-ash-column.jpg on http://www.livescience.com/imageoftheday/siod_080509.html on 8/12/10. 8/12/10. • Fine particles of igneous rock ejected during a volcanic eruption. • Since volcanic ash is quickly deposited over a large area, it serves as an excellent time marker. Objective #6 • Using pages 8 & 9 of ESRT, interpret geologic history and tell important events in each Era, Period and Epoch. C. GEOLOGIC TIME SCALE • Geologists have subdivided geologic time into units called eons. • Eons are subdivided into eras. Eras are split into periods and periods are broken into epochs. Image taken from http://www.cerritos.edu/esci/tutor/On-Line_lecture_notes/Earth_History/Unit_7_Time_Scale.htm on 8/12/10. • The eons, eras, periods and epochs of geologic history are found in the ESRT on page 8&9. • The three eons are Phanerozoic, Proterozoic, Archean. ESRT p8&9 I. Geologic Eras • The four eras are Cenozoic, Mesozoic, Paleozoic, Precambrian. Interactive Geologic Timeline Precambrian or Pre-Paleozoic Era • about 85% of total geologic time of Earth’s history • very little fossil evidence from this era since the living organisms were small, simple and soft bodied like algae and bacteria.
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