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Topic: Geologic timescale

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	Geologic time scale - Wikipedia, the free encyclopedia
		The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth.
		The table of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geologic Survey.
		Because geologic units occurring at the same time but from different parts of the world can often look different and contain different fossils, there are many examples where the same period of time was historically given different names in different locales.
	www.wikipedia.org /wiki/Geologic_timescale (1711 words)

	Encyclopedia: Paleozoic (Site not responding. Last check: 2007-10-21)
		The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 490 million years BP with the beginning of the Ordovician period.
		The Devonian is a major division of the geologic timescale that extends from the end of the Silurian period (360 million years ago (mya)) to the beginning of the Mississippian subperiod of the Carboniferous (408.
		Geologically, the Paleozoic starts shortly after the breakup of a supercontinent called Rodinia and at the end of a global ice age.
	www.nationmaster.com /encyclopedia/Paleozoic (1947 words)

	geologic timescale. The Columbia Encyclopedia, Sixth Edition. 2001-05
		Of the numerous timescales, the most common is based on geologic time units, which divide time into eras, periods, and epochs.
		Each division is based on a specific set of geological or paleontological conditions that make it different from the other divisions, such as varying rock type or fossils within the strata.
		Each geologic time chart varies, depending on the latest findings dating rocks and fossils of that particular age, or on the country where the chart originated.
	www.bartleby.com /65/ge/geolog-ts.html (201 words)

	Geologic timescale - Encyclopedia.WorldSearch (Site not responding. Last check: 2007-10-21)
		The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy.
		When used in formal writing, specific geological and historical periods and events are capitalized.
		This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where we would most like to have them.
	encyclopedia.worldsearch.com /geologic_time.htm (456 words)

	Geologic Timescale (Site not responding. Last check: 2007-10-21)
		Geologic Time USGS on-line publication about the relative and radiometric geologic time scales, age of the earth, index fossils, and related topics.
		Bedrock Geologic Map of Rhode Island A reproduction of the state geological survey's map, with a summary description of the state's geologic history.
		Carbon-Dioxide Sequestration in Geologic Media Texas Bureau of Economic Geology describes its research initiatives on the potential to sequester carbon in saline geologic formations and abandoned oil/gas reservoirs.
	www.serebella.com /encyclopedia/article-Geologic_Timescale.html (233 words)

	Geological Time Scale
		The numerically calibrated geologic time scale has been continuously refined since approximately the 1930s (e.g., Holmes, 1937), although the amount of change with each revision has become smaller over the decades (see fig.
		The overall duration and relative length of these large geologic intervals is unlikely to change much, but the precise numbers may "wiggle" a bit as a result of new data.
		Geologic time is finely subdivided through most of the Phanerozoic (see Harland et al.
	www.talkorigins.org /faqs/timescale.html (669 words)

	History of Geologic Time Scale
		This was the idea that natural geologic processes were uniform in frequency and magnitude throughout time, an idea known as the "principle of uniformitarianism".
		For the next major contribution to the geologic time scale we turn to William Smith, a surveyor, canal builder, and amateur geologist from England.
		When first proposed as a division of geologic time, the beginning of the Phanerozoic (approximately 543 million years ago) was thought to coincide with the beginning of life.
	www.ucmp.berkeley.edu /exhibit/histgeoscale.html (789 words)

	"Understanding the Geologic Timescale"
		Theory: The geologic time scale is a work in process that began in the late 1600’s with the work of a Danish monk, Nicholas Steno.
		The geologic time scale is not a dead set of facts and figures, it is an engaging work in progress where new discoveries are made now that affect our understanding of the world we live in.
		Purpose: The purpose of this unit is to understand the how the geologic time scale was developed, investigate the 11 periods of time and comprehend the vast expanse of time of the Earth’s existence.
	hyper.vcsun.org /HyperNews/nherr/thread.pl/csp_lesson_plans_2001/26.html (2484 words)

	The Geologic Timescale (Site not responding. Last check: 2007-10-21)
		The Phanerozoic eon is further subdivided into three eras: the Paleozoic, Mesozoic, and Cenozoic.
		These subdivisions were devised on the basis of fossil and geologic evidence of global change.
		By moving your mouse over each era you can see the divisions into the different periods and clicking on the timescale will bring you to a text on some of the major events that took place.
	www.mnh.si.edu /anthro/humanorigins/faq/gt/gt_scale.html (250 words)

	Palaeos Timescale: The Geological Time-Scale (Site not responding. Last check: 2007-10-21)
		Scientists divide the Earth into a number of periods - the "Geological time-scale", according to the rock types and sort of fossils found in each one.
		The Geological time-scale can also be used to define the major stages in the history of life on Earth.
		Most recently, in the blink of an eye geologically speaking, this era saw the rise of Man (Homo erectus, Neanderthal and Cro Magnon) and use of stone tools and fire, the extinction of Megafauna, and civilization and human activities that have transformed the globe, but at a cost of great environmental destruction.
	www.palaeos.com /Timescale (960 words)

	Lunar geologic timescale (Site not responding. Last check: 2007-10-21)
		The lunar geologic timescale divides the history of Earth 's Moon into six generally recognized geologic period s:
		Pre-Nectarian Epoch: -4550 MY to -3920 MY The values for these dates remain in some dispute, as the divisions are based on the dates when various significant lunar geological events occurred and it is difficult to pinpoint them exactly.
		geologic lunar lunar eclipse lunar legend lunar month lunar cycles lunar phase lunar cycle lunar calendar lunar game lunar phase calenda lunar lander simulator lunar excursion module
	www.serebella.com /encyclopedia/article-Lunar_geologic_timescale.html (338 words)

	Age Of The Earth
		The older of the two dating methods, the geologic timescale, is actually a circular argument and is therefore considered by many scholars to be weak.
		Nevertheless, the geologic timescale was thought to have been redeemed and refined with the advent of radiometric dating.
		The geologic column is the older of the two dating methods employed by scientists to determine the age of the earth.
	www.allaboutcreation.org /age-of-the-earth-n.htm (543 words)

	CVO Menu - The Geologic Time Scale
		An era of geologic time from the beginning of the Tertiary period to the present.
		An era of geologic time, from the end of the Precambrian to the beginning of the Mesozoic.
		This includes about 90% of all geologic time and spans the time from the beginning of the earth, about 4.5 billion years ago, to 544 million years ago.
	vulcan.wr.usgs.gov /Glossary/geo_time_scale.html (670 words)

	Palaeos Geochronology: Glossary of Geological Timescale Terms (Site not responding. Last check: 2007-10-21)
		The crust of ocean basins was assumed to be relatively immobile.
		geologic column The arrangement of rock units in the proper chronological order from youngest to oldest.
		Precambrian An informal term to include all geologic time from the beginning of the Earth to the beginning of the Cambrian period 570 million years ago.
	www.palaeos.com /Geochronology/gcglossary.html (1790 words)

	Geologic timescale -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-21)
		The geologic timescale is used by (A specialist in geology) geologists and other scientists to describe the timing and relationships between events that have occured during the (A record or narrative description of past events) history of the (The 3rd planet from the sun; the planet on which we live) Earth.
		The (The 3rd planet from the sun; the planet on which we live) Earth is thought by geologists to be about 4570 million years old.
		This is largely due to uncertainties in (Click link for more info and facts about radiometric dating) radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful.
	www.absoluteastronomy.com /encyclopedia/G/Ge/Geologic_timescale.htm (2369 words)

	Geologic Time
		By the middle to late nineteenth century most of the periods and epochs of the geologic timescale were defined.
		The rock systems described in the field could be thought of in terms of geologic time as geologic periods.
		However, there was no clear idea as to how much time the geologic timescale represented, especially for the older rocks that the Cambrian system lay on.
	www.columbia.edu /~vjd1/geol_time.htm (1475 words)

	Lecture 7 (Site not responding. Last check: 2007-10-21)
		century), the geologic timescale was strictly a scheme of relative ages.
		The modern Geologic Timescale is based upon a combination of radiometric and relative ages.
		Because the earth is very geologically active, no rocks have been preserved unchanged since its formation.
	www.unc.edu /gform-links/courses/2000fall/geol018-001/Lecture7.html (404 words)

	Geologic Time
		The Geologic Timescale was initially built from many observations of rock sequences from many parts of the world; no single locality contains the entire geologic time sequence, and correlation of geologic units across different localities allowed geologists to construct a composite timescale.
		The guiding principle followed by many geologists in the 1800's was that current rates of geologic processes were more likely than not to be similar to those in the past - this principle is called uniformitarianism, and was proposed by geologist James Hutton.
		Geologists immediately started determining the ages of volcanic rock layers that were interbedded with the fossil-containing sedimentary rocks that were used to determine the first geologic timescale, adding absolute ages to the geologic eras and periods.
	www.geology.wisc.edu /homepages/g100s2/public_html/geologic_time.htm (686 words)

	Mesozoic (Site not responding. Last check: 2007-10-21)
		The Mesozoic is one of three geologic timescalegeologic eras of Phanerozoic eon (geology)eon.
		The Mesozoic includes three Geologic Periods; from oldest to youngest, the Triassic, Jurassic and Cretaceous.
		Geologically, the Mesozoic starts with almost all the Earth's land collected into a supercontinent called Pangaea.
	www.infothis.com /find/Mesozoic (452 words)

	Geologic Timescale Encyclopedia Article, Definition, History, Biography (Site not responding. Last check: 2007-10-21)
		Looking For geologic timescale - Find geologic timescale and more at Lycos Search.
		Find geologic timescale - Your relevant result is a click away!
		The Earth is thought by geologists to be about 4570 million years old.
	www.alienartifacts.com /encyclopedia/Geologic_timescale (1850 words)

	Search Encyclopedia.com
		Mesozoic era Mesozoic eramĕzand180;ezō´Ĭk [Gr.,=middle life], major division of geologic time (see Geologic Timescale, table) from 65 to 225 million years ago.
		Jurassic period Jurassic periodjerăs´Ĭk [from the Jura Mts.], second period of the Mesozoic era of geologic time, lasting from 213 to 144 million years ago.
		At the start of the Jurassic most of the continents were joined together until the Atlantic began to form and the Americas split off from Africa.
	www.encyclopedia.com /search.asp?target=dinosaur&rc=10&fh=33&fr=11 (513 words)

	The New Timescale
		Almost all of the dates on my 1994 Pan Terra geologic chart are wrong by a few million years.
		In 1987, the period was estimated to have ended 131 million years ago, based on the amount of potassium that had been converted into argon in a mineral called glauconite.
		But it was later discovered that argon seeps out of glauconite, making the mineral seem younger than it actually is. The new timescale used potassium-argon dating of basalt to put the end of the Jurassic at 145.5 million years ago.
	www.ridgecrest.ca.us /~do_while/sage/v8i9n.htm (426 words)

	Selected Geology, Links for Palaeobotanists
		As the basis of the BGS Geological Timechart they have chosen the timescale of Gradstein and Ogg (1996) for the Phanerozoic and that of Cowie and Bassett (1989) for the Proterozoic (Precambrian).
		ICS (within the International Union of Geological Sciences) is the only organisation concerned with stratigraphy on a global scale.
		This multi-year project summarized the history and status of boundary definitions of all geologic stages, compiled integrated stratigraphy (biologic, chemical, sea-level, magnetic, etc.) for each period, and assembled a numerical age scale from an array of astronomical tuning and radiometric ages.
	www.uni-wuerzburg.de /mineralogie/palbot/geology/geology.html (961 words)

	Geologic Time Scale (Site not responding. Last check: 2007-10-21)
		efore modern radiometric dating techniques made it is possible to determine rock ages empirically, the geologic record was divided into relative time units based on correlation of the rock formations, mostly by the index fossils they contained.
		This was the basis for the modern Geologic Time Scale, a concoction of names like Cretaceous, Jurassic, and Ordovician, assigned by early European geologists.
		This is accomplished by measuring the amounts of certain radioactive isotopes contained in the rocks (usually limited to igneous rocks), in relation to the amount of corresponding decay isotopes (daughter products) that are present.
	www.clearlight.com /~mhieb/WVFossils/GeolTimeScale.html (147 words)

	Geologic Timescale, 1989 Book from Books.co.uk
		This book is the planned successor to A Geologic Time Scale by W. Harland, A. Cox, P. Llewellyn, C. Pickton, A. Smith and R. Walters published in 1982.
		The state of the art 1989 is thus presented; but the data assembled provide a source of reference which will serve for some years.
		The work develops and assesses a new calibration of the geologic time scale employing a new database.
	www.books.co.uk /geologic_timescale_1989/0521383617.html (167 words)

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