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Topic: Geologic time scale


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In the News (Wed 23 Apr 14)

  
  Geological Time Scale
Think of relative time as physical subdivisions of the rock found in the Earth's stratigraphy, and absolute time as the measurements taken upon those to determine the actual time which has expired.
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.
The time scale is depicted in its traditional form with oldest at the bottom and youngest at the top -- the present day is at the zero mark.
www.talkorigins.org /faqs/timescale.html   (669 words)

  
  The Geologic Time Scale
An era of geologic time from the beginning of the Tertiary period to the present.
An era of geologic time between the Paleozoic and the Cenozoic.
An era of geologic time, from the end of the Precambrian to the beginning of the Mesozoic.
scienceviews.com /dinosaurs/geologictime.html   (726 words)

  
  Geologic time scale - Wikipedia, the free encyclopedia
The geological time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the History of Earth.
Different spans of time on the time scale are usually delimited by major geological or paleontological events, such as mass extinctions.
Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering, erosion, sedimentation, and lithification.
en.wikipedia.org /wiki/Geologic_time_scale   (2023 words)

  
 CalendarHome.com - Geologic time scale - Calendar 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.
Different spans of time on the time scale are usually delimited by major geologic or paleontologic events, such as mass extinctions.
encyclopedia.calendarhome.com /Geologic_timescale.htm   (1813 words)

  
 Geologic Time Scale
The time scale at left is both a reference and a key to the display cases at the museum ­ click on a geologic period to go to that case.
This geologic time scale is based upon data from Harland et al., (1990) and Gradstein and Ogg, (1996).
The time scale is depicted in its traditional form with oldest at the bottom, and youngest at the top ­ the present day is at the zero mark.
www.humboldt.edu /~natmus/lifeThroughTime/Timeline/TimeScale.html   (419 words)

  
 Radiometric Dating and the Geological Time Scale
One of the earliest (1759) relative time scales based upon this observation was the subdivision of the Earth's stratigraphy (and therefore its history), into the "Primary", "Secondary", "Tertiary", and later (1854) "Quaternary" strata based mainly on characteristic rock types in Europe.
Various attempts were made as far back as the 1700s to scientifically estimate the age of the Earth, and, later, to use this to calibrate the relative time scale to numeric values (refer to "Changing views of the history of the Earth" by Richard Harter and Chris Stassen).
Every time a rock is picked up it is a test of the predictions made by the current understanding of the geological time scale.
www.talkorigins.org /faqs/dating.html   (5229 words)

  
 LAB 6 GEOLOGIC TIME and the FOSSIL RECORD
Through the early years of the 1800s, these local observations were elaborated upon and gradually applied on a global scale, and by the last half of that century a relative time scale had been constructed that could be applied to most parts of the world.
The importance of this first real geologic map was the fact that it portrayed the various rock units that Smith recognized in a logical fashion and included a description of the rocks and fossils present in each unit.
At the time, the entire thickness of the rock record was not known, the significance of post-depositional compaction was not taken into account, and it was poorly understood that the rocks themselves represent only a fraction of the time; a considerable amount of time is represented by bedding planes between the layers of rock.
www-rohan.sdsu.edu /~rhmiller/geologictime/GeologicTime.htm   (8037 words)

  
 History of Geologic Time Scale
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.
The time before the Phanerozoic is usually referred to as the Precambrian, and exactly what qualifies as an "eon" or "era" varies somewhat depending on whom you talk to.
www.ucmp.berkeley.edu /exhibit/histgeoscale.html   (789 words)

  
 Geologic Time: Radiometric Time Scale
Interweaving the relative time scale with the atomic time scale poses certain problems because only certain types of rocks, chiefly the igneous variety, can be dated directly by radiometric methods; but these rocks do not ordinarily contain fossils.
Most sedimentary rocks such as sandstone, limestone, and shale are related to the radiometric time scale by bracketing them within time zones that are determined by dating appropriately selected igneous rocks, as shown by a hypothetical example.
Many points on the time scale are being revised, however, as the behavior of isotopes in the Earth's crust is more clearly understood.
pubs.usgs.gov /gip/geotime/radiometric.html   (1295 words)

  
 Geologic ages of earth history - encyclopedia article - Citizendium
Geological ages, in common use, refer to periods of marked change in the processes and events in the entire history of the earth.
The geologic time is most commonly measured with methods based on the radioactive decay of long-lived unstable isotopes present in the earth's crust, and is expressed in Ma (i.e., millions of years ago).
The identification, description and quantification of geologic time involves, in addition to geochronometry, the fields of stratigraphy (the sub-discipline of geology studying the relationships of strata in time and space), biostratigraphy (the use of fossils for ordering and correlating strata in relative time), and geochronology (the study of geological time itself).
en.citizendium.org /wiki/Geologic_time_scale   (3131 words)

  
 Geologic time scale
The geological time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of Earth.
Different spans of time on the time scale are usually delimited by major geological or paleontological events, such as mass extinctions.
Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering, erosion, sedimentation, and lithification.
www.medbib.com /Geologic_time_scale   (3470 words)

  
 Geologic Time
The immensity of geologic time is very difficult to appreciate from our human perspective, but appreciation is necessary to understand the history of the Earth.
Geologic time was originally subdivided based on the relative positions of sedimentary rocks.
The Geologic Column is the chronologic arrangement of rock units from oldest at the bottom to youngest at the top.
www.geo.ua.edu /intro03/time.html   (1599 words)

  
 Geologic Time Scale — plone.org   (Site not responding. Last check: )
Geologic Time Scale is a graphics generating product that uses the Report Lab toolkit for graphics file creation and custom methods to emit SVG code.
For an example of a phylogenetic diagram on a time scale, see this one: palaeo.gly.bris.ac.uk/Palaeofiles/Triassic/ammon.htm that includes abundance range bars also.
It is common to show phylogenetic lineages as "bubble" plots for changing abundance or diversity through time, with the "bubbles" being smooth-sided shapes showing the abundance history of the lineage.
plone.org /products/geologictimescale   (1363 words)

  
 Geologic Time Scale
The modern geologic time scale shown in Figure A1 was nearly complete by the end of the 19th century and was based on stratigraphic and fossil studies in northern Europe and the United States.
Originally, geologic time scale divisions were based on the natural breaks in the stratigraphic column.
The longest divisions of geologic time are the eras.
southwest.library.arizona.edu /azso/back.1_div.1.html   (1090 words)

  
 The Geologic Time Scale
The study of the Earth from the beginning of time to the present has been the task of geologists who attempt to unravel the events that have shaped our planet as it is today.
An era of geologic time from the beginning of the Tertiary period to the present.
An era of geologic time between the Paleozoic and the Cenozoic.
www.scienceviews.com /dinosaurs/geologictime.html   (717 words)

  
 Palaeos Timescale: Detailed Geological Timescale
The Geological Time-Scale is hierarchical, consisting of (from smallest to largest units) ages, epochs, periods, eras and eons.
The Geological time-scale is usually represented as a vertical table to be read from the bottom up; the oldest eras and periods at the bottom, the youngest at the top.
Geologic Ages of Earth History - Jeff Poling - a detailed and up to date chart showing every era, period, epoch and age of the geological time scale, together with time when began and during in millions of years.
www.palaeos.com /Timescale/timescale.html   (546 words)

  
 Geologic Time
The "best" age for the Earth is based on the time required for the lead isotopes in four very old lead ores (galena) to have evolved from the composition of lead at the time the Solar System formed, as recorded in the Canyon Diablo iron meteorite.
The probability of a parent atom decaying in a fixed period of time is always the same for all atoms of that type regardless of temperature, pressure, or chemical conditions.
The time required for one-half of any original number of parent atoms to decay is the half-life, which is related to the decay constant by a simple mathematical formula.
www.desertusa.com /mag03/Jan/time.html   (1360 words)

  
 DRAM, FGS, Geologic Time Scale
Geologists use a geologic time scale to describe the 4.5 billion years that have passed since the earth formed.
The geologic time scale is constructed with the present time at the top, and progressively older time divisions as you read down the scale.
A hierarchy of time period categories is used to characterize geologic time.
www.dep.state.fl.us /geology/geologictopics/rocks/time_scale.htm   (313 words)

  
 Geologic Time Scale - Geological Time Line - Geology.com
This is because geologic time is divided using significant events in the history of the Earth.
Eons are the largest intervals of geologic time and are hundreds of millions of years in duration.
Finer subdivisions of time are possible and the periods of the Cenozoic are frequently subdivided into epochs.
geology.com /time.htm   (428 words)

  
 Deep Time
Particularly that the geologic time scale was first conceived through an understanding of the relative age of fossils.
Each section of the geologic column was given a name corresponding to localities with complete geologic sections or to characteristics of the period.
The numerical geologic time scale is in a constant state of flux as geochronologists (geologists who date rocks) find (or bracket) more precise ages for the fossiliferous rocks used to construct the original geologic column.
serc.carleton.edu /quantskills/methods/quantlit/DeepTime.html   (2277 words)

  
 Geologic Time Scale
A graphic demonstration of the enormous extent of geologic time compared to recent time.
The time scale is a combination of actual numbers (for the eons and such) and approximate dates from a time scale (for events, such as "early horses"), both from:
Many events cannot be pinpointed (the geologic record is not perfect or complete), and in any case, most of the "dividing lines" are probably gradual changes, occurring over many thousands or even millions of years.
www.nthelp.com /eer/HOAtimetp.html   (279 words)

  
 Geologic Time: The Geological Time Scale
Geologists used relative time for a couple of centuries to arrange geologic events in the correct sequence (see Relative Time).
Those species that were able to adapt to the changes survived to thrive in the Mesozoic era that followed whereas others breathed for the last time and their remains became part of the fossil record.
time intervals represent numerical time and were determined after the relative order of the geologic time scale was established.
www.mhhe.com /earthsci/geology/mcconnell/gti/time.htm   (1463 words)

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