Geological timescale


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Aeonothem Arathem system Age
( mya )
P
h
a
n
e
r
o
z
o
i
k
u
m


Duration:

541
Ma
Cenozoic
Cenozoic
Duration: 66 Ma
quaternary 0

2.588
Neogene 2,588

23.03
Paleogene 23.03

66
Mesozoic
Mesozoic
period: 186.2 Ma
chalk 66

145
law 145

201.3
Triad 201.3

251.9
Paleozoic
Paleozoic
period: 288.8 Ma
Perm 251.9

298.9
Carbon 298.9

358.9
Devon 358.9

419.2
Silurian 419.2

443.4
Ordovician 443.4

485.4
Cambrian 485.4

541
P
r
o
t
e
r
o
z
o
i
k
u
m


Duration:

1959
Ma
Neoproterozoic
Jungproterozoikum
Duration: 459 Ma
Ediacarium 541

635
Cryogenium 635

720
Tonium 720

1000
Mesoproterozoic
Mittelproterozoikum
Duration: 600 Ma
Stenium 1000

1200
Ectasium 1200

1400
Calymmium 1400

1600
Paleoproterozoic
Altproterozoikum
Duration: 900 Ma
Statherium 1600

1800
Orosirium 1800

2050
Rhyacium 2050

2300
Siderium 2300

2500
A
r
c
h
a
i
k
u
m


Duration:

1500
Ma
Neo-Archaic
Duration: 300 Ma
2500

2800
Mesoarchean
Duration: 400 Ma
2800

3200
Paleoarchean
Duration: 400 Ma
3200

3600
Eoarchic
Duration: 400 Ma
3600

4000

H
a
d
a
i
k
u
m


Duration:
600
Ma
4000








4600

The geological time scale is a hierarchical division of the earth's history . Both the hierarchy levels and the time periods are named. The older periods of time (“ Precambrian ”) are less subdivided than the younger ones, and their subdivision is based solely on tectonic phases. With the beginning of the Phanerozoic ("age of visible [animal] life") 541 million years ago, the continuous fossil record began, which enabled a more differentiated classification using the methods of biostratigraphy . The boundaries of the time segments are assigned an absolute (numerical) age using the methods of geochronology , mainly radiometric .

Conventionally, the chronological sequence is shown from bottom to top, just as the series of sedimentary rocks can be found within an idealized tectonically undisturbed rock profile.

A version of the geological time scale that is generally accepted in the international geoscientific community is being developed and published by the International Commission on Stratigraphy (ICS). The table on the right shows the stratigraphic units according to the ICS standard in a compact, not to scale representation (the units of the two lowest hierarchical levels are not included). An extensively annotated table is here to find.

Dual nomenclature

The history of the earth spans a gigantic period of time, which is divided into hierarchically structured intervals. In the global standard time scale established by the International Commission for Stratigraphy (ICS), to which all other global scales are oriented, the hierarchical structure follows two concepts that are used in parallel and are relatively similar to one another: geochronology and chronostratigraphy . The geochronological breakdown refers exclusively to the time periods of the earth's history ("geological age", geological time). Chronostratigraphy, on the other hand, refers to the geological tradition , i.e. to the entirety or a certain subset of the rocks that have been handed down from such a period.

The geochronological and chronostratigraphic concepts only differ in terms of nomenclature in the naming of the hierarchical levels.

The names of the geochronological hierarchy levels are:

  • Aeon (English eon , Greek αἰών Aion "eternity")
    • Era (English era , the medieval Latin aera "age")
      • Period (English period , Greek περίοδος períodos "repeating section")
        • Epoch (English epoch , Greek ἐποχή epochḗ "breakpoint")
          • Age (English age )

The scientifically unspecified, general term geological age usually stands for a larger period of geological history. As a rule, it refers to the eras and periods of the geological time scale and thus to intervals of at least two, but mostly between 40 and 250 million years.

The names of the chronostratigraphic hierarchy levels are:

The names of the intervals are identical in both concepts.

Illustrative example: The statement "The first terrestrial vertebrates lived in the Devonian " refers to geological time and the geochronological concept of the Devonian interval (period). The statement "In Devon Greenland numerous remains of early terrestrial vertebrates have been found" refers to the geological tradition and the chronostratigraphic concept of the Devonian interval (system). In the latter case, the name of the period could also be replaced by the naming of one or more lithostratigraphic units (“In the [Devonian] Britta-Dal formation of Greenland numerous remains of early terrestrial vertebrates were found”) and the stratigraphic indication “Devonian” is more precise using the attributes “upper” or “lower” ( “In the upper Devonian Greenland numerous remains of early terrestrial vertebrates were found” or “In the Upper Devonian Britta-Dal formation of Greenland [...]” ). When using the geochronological concept of an interval, the specification is to be made using the attributes “early” or “late” (“The first land vertebrates lived in the late Devonian”) .

Both concepts are closely linked, because absolute (numerical) age or time information can only be obtained from geologically transmitted material, usually through radiometric dating . A strict separation of geochronology and chronostratigraphy is therefore seldom maintained in practice. The current version of the ICS standard time scale bears the title International Chronostratigraphic Chart , although the table header also contains the names for the geochronological hierarchy levels.

Regional scales

In different regions of the world (North America, Western Europe, Eastern Europe, China, Australia), regional scales are used in addition to the global standard time scale. These differ from each other and from the standard time scale with regard to the naming of some intervals, mostly the middle and lower hierarchical levels, as well as with regard to the absolute (numerical) age of some interval limits. In doing so, they take into account the particularities of geological tradition in the corresponding region. It is therefore a question of "purely" chronostratigraphic tables. Individual sections of these regional scales can in turn differ from one another on a subregional scale.

For example, different names are used for the cold periods of the Pleistocene of North America, the North German Plain, and the Alpine region, and the Permian of Central Europe, called Dyas , begins earlier than the Permian of the global timescale and other regional scales.

Definition of the unit limits

The “golden nail”, which marks the lower limit of the Ediacarium and thus the upper limit of the cryogenium in the reference profile (digestion of a dolomite sequence at Enorama Creek, South Australia). Sampling sites can be seen above and to the left of the marking.

The boundaries of the units or intervals of the Phanerozoic are primarily defined based on the appearance ( first appearance date , FAD) or disappearance ( last appearance date , LAD) of certain animal species in the fossil record (a so-called bioevent ). These are always the remains of marine organisms because, on the one hand, marine sediments, especially shelf sediments, are much more common in geological tradition than continental sediments, and on the other hand, because shelf sediments are on average significantly more fossilized than continental sediments. Only the base, the lower limit, and one unit are defined, and the upper limit is identical to the base of the next unit. In addition to the primary labels the units are additionally defined by secondary markers to locate the unit boundary in sediments that the primary marker facies caused (see FIG. →  depositional environment should allow not included). In addition to fossils, geochemical and / or magnetostratigraphic anomalies also serve as markers. For a large part of the units of the geological time scale in the rank of a level, special outcrops have meanwhile been determined, in whose sedimentary rock layers the correspondingly defined level lower limit is contained with the primary marker and possibly several secondary markers and is visually identified (“golden nail”). This reference profile is called the Global Stratotype Section and Point (GSSP). The lower limit of a higher-ranking unit (series, period, etc.) is determined by the lower limit of the lowest level it contains. The lower limit of the Cretaceous Period is consequently defined by the same criteria that define the lower limit of the Berriasium .

In the course of the 20th century, methods were developed with the help of which it became possible to date certain rocks, usually of igneous origin, absolutely (numerically) radiometrically . The age of a rock dated in this way indirectly gives the absolute minimum or maximum age of the fossil-bearing sedimentary rocks on top or below it, thus also the approximate absolute age of the fossils contained therein, and, through extensive worldwide sampling, finally also the absolute age of those fossils that contain the Define the boundaries of the units of the geological time scale. Accordingly, the absolute ages of these units are known as well as the absolute periods of time over which they extend.

The grouping of the ages / stages to periods / systems and these in turn to eras / aera topics is based on common features of the fossil record in the sedimentary rocks of these units. The boundaries of higher-ranking units therefore often coincide with significant mass extinctions , as a result of which the composition of the fossil fauna changes significantly, especially at higher taxonomic levels . The geological time scale thus also depicts the history of evolution .

The division of the Precambrian and thus the longest section of the earth's history, with the exception of the Ediacarian, cannot be based on fossils, because there are no fossils or at least no usable fossils in these rocks. Instead, an “artificial” structure is used, which is based on mean values ​​of radiometrically determined age data from tectonic periods of rest. These values, rounded to a full 50 or 100 million years, are called the Global Standard Stratigraphic Age (GSSA).

For the older units of the Precambrian, the geological tradition worsens with age. The exogenous and endogenous processing ("recycling") of the earth's crust (see →  rock cycle ), which has been ongoing for billions of years, has destroyed a large part of these early rocks. The events in the Hadean are almost completely unknown because no rocks, but only a few detritic zircons, including more recent rocks, have come down to us from this period. The Hadean is the only unit of the geological time scale for which no base is defined.

History of the geological scales

The Englishman Adam Sedgwick coined several names of chronostratigraphic units that are still in use today.

As early as the 17th century, it was known from the work of Nicolaus Steno that sedimentary rocks are layered chronologically. But there was no method of determining the periods or points in time at which a layer was deposited. Fossil finds of marine life in the high mountains also made it possible to conclude at an early stage that the earth is not immutable but is subject to profound upheavals. At the time, however, this thought was strange for many contemporaries, because the biblical creation story was still largely decisive for the age of the earth (see, among others, → Ussher-Lightfoot calendar ), although naturalists such as Georges Buffon or James Hutton in the second half of the 18th century deduced from their research that the earth must be much older. How old it actually is, however, was still unknown, and there was also no way of structuring geological time for the time being.

With their systematic work, early paleontologists such as William Buckland and Georges Cuvier finally pave the way for the knowledge that layers with the same fossil content must have formed at the same point in time in the history of the earth. The Englishman William Smith developed a stratigraphic table for his geological map of Great Britain on this basis at the end of the 18th and beginning of the 19th century.

In the course of the 19th century, modern stratigraphy gradually developed: geologists throughout Europe and North America studied, categorized and correlated the rock strata in their countries on the model of William Smith and published maps, stratigraphic tables and treatises with the results of their work. In this way, the geological tradition of different countries and regions could be compared with one another, and the realization quickly matured that layers can also be correlated on a supra-regional scale. For the respective correlatable sequences (intervals), names were established that were originally coined for regional strata, for example by Jean Baptiste Julien d'Omalius d'Halloy the Terrain Cretacé (Anglicized Cretaceous , Germanized chalk ) for certain strata of the Paris basin , the in a similar training with similar fossil content u. a. were already known or subsequently identified in other regions of France, England, the Netherlands, Germany, Poland and Denmark. Adam Sedgwick and John Phillips recognized that these intervals can be summarized into larger units due to similarities in their fossil record and coined the terms Paleozoic , Mesozoic and Cenozoic , which were the generic terms primary and secondary used until then and Tertiary , except for the latter. As early as the middle of the 19th century, there was a stratigraphic nomenclature that corresponded in essential points to that used in all current time scales. There were also numerous attempts in the 19th century to realistically estimate the geological time periods - for example using erosion and sedimentation rates - and the idea that the earth is many millions of years old was increasingly accepted. For example, the famous Charles Lyell estimated the time since the beginning of the Cambrian to be 240 million years in the 10th edition of his Principles of Geology (1867).

The geological time scales have been continuously developed to this day. In particular, the discovery of radioactivity in the 20th century and that radionuclides can be used for the absolute dating of rocks heralded a new phase in the development of time scales. Now the unit limits could be assigned a numerical age and the enormous ranges of geological time since the formation of the earth (English deep time ) could be precisely determined (see illustration of the time periods ).

While essential revisions of the timescale took place for a long time as part of the “normal” scientific discourse (suggestions published in specialist journals that were subsequently either accepted and taken up, ignored or actively criticized and rejected by other authors), they are now among those with international leaders Sub-commissions of the International Commission on Stratigraphy (ICS), a sub-organization of the International Union of Geological Sciences (IUGS) and decided by majority vote. They are then submitted to the appropriately authorized committees of the respective superordinate organization for voting. This is to ensure that the current version of the geological time scale is supported by the majority of leading geoscientists worldwide and thus finds the greatest possible acceptance and broadest possible use in geoscientific research and teaching. A current version of the global timescale is published by the ICS on its website at regular intervals, and every several years a detailed global timescale with extensive commentary appears, which also includes the correlation with regional scales.

One of the more recent changes in the chronostratigraphic nomenclature concerns the abolition of the term " tertiary " for the older and largest part of the Cenozoic era of the global time scale in favor of a two-way division of this period into paleogene and neogene . Another change, which was preceded by a controversial debate about the retention of the name "Quaternary", is the accompanying shift of the Neogene / Quaternary or Neogene / Pleistocene boundary by almost 800,000 years down, from 1.8 to 2.59 mya with the incorporation of the Gelasium into the Pleistocene. A proposed, but not yet adopted revision concerns the reorganization of the Precambrian, in which the unit boundaries, as is common for the Phanerozoic, are defined by GSSPs instead of GSSAs (see definition of unit boundaries). Some scientists, especially representatives of the "Global Change research community", ie those researchers who are directly concerned with the anthropogenically influenced change in the Earth system, suggest a new unit as the youngest member of the time scale, the Anthropocene . However, there is no agreement about its beginning and for the vast majority of geologists, a unit lasting only a few hundred years would have no practical use.

Scale ruler and cutouts

The Phanerozoic is structured as the "Age of Fossils " and due to the generally better geological tradition compared to the Precambrian. In general: the younger a part of the geological tradition, the finer it is structured or the shorter the duration of the chronostratigraphic units that contain it. Therefore, the scale in some representations changes within the geological time scale, mostly twice: once at the Precambrian-Cambrian boundary and once at the Cretaceous-Paleogene boundary (formerly: Cretaceous-Tertiary boundary).

Entire age Enlargement of the Phanerozoic Enlargement Cenozoic


Also for a better presentation of the units of the lowest ranks and possible sub-units, individual sections, usually the periods / systems, are shown in separate tables.

Paleobotanical timescale

The division of the paleobotanical time scale is not based, like that of the geological time scale, on the evolution of marine invertebrates, but on the evolution of the plant world, especially terrestrial plants. It also contains only one hierarchy level, which corresponds to the eras / aera topics of the geological time scale. The names of these "eras" are analogous to those on the geological time scale, but do not end with -zoikum , but -phytikum . Instead of the Paleozoic, a distinction is made between two “eras”: Eophytic (Cambrian and Ordovician) and Paleophytic (Silurian to Permian). Because the evolution of terrestrial plants does not correlate with the evolution of marine invertebrates, the limits of the paleobotanical "eras" only roughly coincide with those of the geological time scale. Thus the neophytic (= cenophytic) began 95 million years ago, with the onset of the dominance of the covering species in the fossil record, while the “neozoic” (= cenozoic) began 65 million years ago with the disappearance of ammonites and belemnites from the fossil record.

Illustration of the time periods

The geological ages span enormous periods of time that can hardly be measured. This can lead to misunderstandings, for example the opinion that there was not enough time for the entire evolution . The following comparisons are used to illustrate the time periods.

Comparison geological age - one day

The table below lists geological events in chronological order in the middle column, which have a key position in the biological and cultural evolution of man. The left column shows the time actually elapsed since the formation of the earth and the right column shows the same periods of time, but scaled down to the duration of a single day (24 hours). In this case, modern humans ( Homo sapiens ) would only appear around 4 seconds before the end of the day.

The time span covered by the geological time scale, scaled down to the duration of one day: The Precambrian does not end until 9:10 p.m.
actually elapsed time
to date [million Years]

geological
event
(origin of / of ...)
scaled down
to a day
remaining time
until the end of the day
Time
0.01 (Holocene) Agriculture and animal husbandry 0.2 s 23: 59: 59.8
0.19 (late Pleistocene) homo sapiens 3.6 s 23: 59: 56.4
2 (early Pleistocene) Homo habilis 38 p 23:59:22
7 (late Miocene) " Pre-humans " 2 min 15 s 23:57:45
20 (early Miocene) Great apes 6 min 23:54
40 (Eocene) Monkeys 12 min 23:48
60 (Paleocene) Primates 18 min 23:42
200 (formerly Jura) mammal 1 h 5 min 22:55
315 (late carbon) Amniotes 1 h 40 min 22:20
360 (late Devonian) Terrestrial vertebrates 1 h 55 min 22:05
425 (Silurian) Bony fish 2 h 15 min 21:45
470 (Ordovician) Vertebrates 2 h 30 min 21:30
600 (Ediacarium) Bilateria 3 h 10 min 20:50
1500 (Mesoproterozoic) Eukaryotes 7 h 17:00
2400 (Neo-Archean) photosynthesis 13 h 11:00
3800 (Eoarchean) Unicellular organisms 20 h 04:00
4570 (Hadaikum) earth 24 hours 00:00

See also

literature

  • Felix M. Gradstein, James G. Ogg, Alan G. Smith (Eds.): A Geologic Time Scale 2004. Cambridge University Press, Cambridge (UK) 2004, ISBN 0-521-78673-8 .
  • Felix M. Gradstein, James G. Ogg, Mark Schmitz, Gabi Ogg (Eds.): The Geologic Time Scale 2012. Elsevier BV, 2012, ISBN 978-0-444-59425-9 .
  • Michael A. Murphy, Amos Salvador (Red.): International Stratigraphic Guide - An abridged version. Episodes. Vol. 22, No. 4, 1999, pp. 255-271 ( online ), pp. 266 ff.

Web links

References and comments

  1. for example the Geologic Time Scale of the Geological Society of America
  2. Lemma Erdzeitalter in the digital dictionary of the German language
  3. Lemma Erdzeitalter in the spectrum-compact dictionary of biology
  4. Note: In fact, the concept of geological time is derived from that of geological tradition. In the German-speaking world, for example, terms such as carbon formation , triad formation , etc. were common when referring to sequences of rocks of a certain relative age. In the meantime, the term formation is more narrowly defined and is no longer used in chronostratigraphy.
  5. International Chronostratigraphic Chart , official website of the ICS (www.stratigraphy.org)
  6. Note: The best known geochemical marker is probably the iridium anomaly at the Cretaceous-Tertiary boundary.
  7. List of all previously defined GSSPs on the ICS website (English) with numerical age, location data, type of stratigraphic marker (s), etc .; a data sheet with further details is linked in the leftmost column
  8. ^ A b M. J. Van Kranendonk, Wladyslaw Altermann, Brian L. Beard, Paul F. Hoffman, Clark M. Johnson, James F. Kasting, Victor A. Melezhik, Allen P. Nutman, Dominic Papineau, Franco Pirajno: A Chronostratigraphic Division of the Precambrian - Possibilities and Challenges. In: Felix M. Gradstein, James G. Ogg, Mark Schmitz, Gabi Ogg (eds.): The Geologic Time Scale 2012. Volume 1, Elsevier BV, 2012, pp. 299–392, doi : 10.1016 / B978-0- 444-59425-9.00016-0 , p. 300
  9. ^ Felix M. Gradstein, James G. Ogg: The Chronostratigraphic Scale. In: Felix M. Gradstein, James G. Ogg, Mark Schmitz, Gabi Ogg (eds.): The Geologic Time Scale 2012. Volume 1, Elsevier BV, 2012, pp. 31–42, doi : 10.1016 / B978-0- 444-59425-9.00002-0 , p. 34
  10. a b Joe D. Burchfield: The age of the Earth and the invention of geological time. In: DJ Blundell, AC Scott (Ed.): Lyell: the Past is the Key to the Present. Geological Society. London, Special Publications. Vol. 143, 1998, pp. 137–143, doi : 10.1144 / GSL.SP.1998.143.01.12 ( Open Access )
  11. ^ Douglas Palmer: Earth Time: Exploring the Deep Past from Victorian England to the Grand Canyon. Wiley, Chichester (England) 2005, ISBN 0-470-02221-3
  12. from an overview of numerous estimates made in the 19th century, given in Charles D. Walcott: Geologic Time, as Indicated by the Sedimentary Rocks of North America. The Journal of Geology. Vol. 1, No. 7, 1893, pp. 639-676 ( JSTOR 30054500 , Open Access )
  13. ^ Subcommission on Quaternary Stratigraphy: Working Group on the "Anthropocene".
This version was added to the list of articles worth reading on July 12, 2005 .