Types of time scales

TimeAbstract

Geochronometric scales

Conclusions

Albian

Aalenian

Artinskian

Arenigian

Middle Ages

Han Dynasty

Satavahana Dynasty

476 AD – 1453 AD

206 BC – 220 AD

200 BC – 236 AD

~ 105 Ma

~ 180 Ma

~ 260 Ma

~ 480 Ma

Partitioning timeNominal and interval scales

Content Events Time

0

100

200

300

400

500

600

700

Time

0

100

200

300

400

500

600

700

Geon (H.P. Woodward, 1929, Pan -Amer. Geol. 51:15-22)

A unit … “taken to represent eitherthe span of the average geologic period,or the thickness of the averagestratigraphic equivalent, a matterof 60,000,000 years, and 50,000 feet[~15 km] of clastic depositions”

Using 543 Ma for the base of the Cambrian,and 11 geologic periods, an updated

value for Woodward’s geon is ~49.4 my

Complex nomenclature

JIN et al., 1991(Jour. of Stratigraphy 15(4):313-315, 320)

Scheme based onequal time intervals,

but with complex nomenclature

and inconsistent divisions:

Units have 3 divisions for300-my eras in Proterozoic,2 divisions for 400-my eras

in Archean

JIN et al., 1991(Jour. of Stratigraphy 15(4):313-315, 320)

Scheme based onequal time intervals,

but with complex nomenclature

and inconsistent divisions:

Units have 3 divisions for300-my eras in Proterozoic,2 divisions for 400-my eras

in Archean

Geon (geological eon) (Hofmann, 1990)

A specified 100-million-year intervalof geologic time, counted backwardfrom the present.

The geon is named for the leftmostpart of the number representing age.

Ages such as 1851 Ma and 1800 Ma belong to Geon 18;the Cretaceous extinction (065 Ma) belongs to Geon 0

Implications

Period/system boundaries approximategeon boundaries

Era/erathem boundaries lie near middle of geons

Parallel, complementary scales

100-my bins (Geon units)

Grenville Province

Metasediments

Time slice maps

Sediments

-- -- -- Inferred SE extent of Laurentiaat end of Geon 16

-- -- -- Inferred SE extent of Laurentiaat end of Geon 14

Sedimentary sequences

Sediments

Temporal classification of principal tectonic elements adjacent to the Slave craton

Hoffman & Hall, 1993, GSC Open File 2559

Geologic map using geon units

Geon gap map

Planetary histories and correlation

Perspectives

Scale of phenomena(adapted from Carey 1962, J. Geol. Soc. India 3:97-105)

H.J. Hofmann, Dept. of Earth and Planetary Sciences, and Redpath Museum, McGill University, Montreal, QC H3A 2A7 hofmann@eps.mcgill.ca

Eons and geons - a simple planetary time scale

A widely used dictionary defines a time scale as "an arrangement of events used as a measure of the relative or absolute duration or antiquity of a period of history or geologic or cosmic time..." (Gove,1986, p. 2395). Different types of scales exist: in increasing order of information content, these are binary, nominal, ordinal, interval, and ratio scales. The Phanerozoic time scale has divisions based on characteristic fossil content and has nominal and ordinal attributes; its chronostratigraphic units are defined at stratotypes, and they are of relative short duration and most have been calibrated radiometrically. The divisions of the Proterozoic time scale proposed by the International Commission on Stratigraphy (Cowie et al., 1989) are of relatively long duration, and are named after geohistorical content and thus viewed as corresponding to chronostratigraphic units; yet, contrary to rules of stratigraphic nomenclature, they are not based on designated stratotypes, but on arbitrary ages with large round numbers.

For overview and integrative studies of planetary evolution during the longest part of Earth history (the Cryptozoic or Precambrian), a universal calendar system with numerical units of appropriately long duration to encompass major geological developments (basin formation, orogenic belts, etc.) is more suitable. A convenient measure of such a geochronometric scale is a unit of 100 million years (geon). Such a simple, numerical, equal-interval scale, coupled with a corresponding simple nomenclature (Hofmann, 1990, 1992, 1999), is preferable and more efficient in conveying long-term evolutionary trends than a system of complex nomenclature (Cowie et al., 1989; Plumb, 1991, 1992). The geon concept has been applied to document the geotectonic development of some regions, such as northwestern Canada, and the Grenville Province, and various authors have long used 100-m.y. bins in compilations illustrating various aspects of geospheric evolution.

In addition to geon unit maps, the geon concept can also be used in the preparation of geon gap maps, which emphasize the time values of contacts or discontinuities between major rock units, by visually and quantitatively portraying their relative magnitude. Such maps may be useful, for example, in the exploration for unconformity-related ore deposits.

8A universal geon interval scale for numerically specified time periods of long duration (bins of 10 a) affords manifold advantages; in essence, such a scale has the benefits of being:1) numerical, direct, and simple, with intervals of equal duration;2) easy to learn, to remember, and to apply, because the numeral part also provides the nominal and ordinal functions - only 1 word needs to be assimilated, instead of necessitating the learning of a multitude of names whose additional requirement is that relative positions also need to be remembered;3) geopolitically neutral by transcending language barriers and jurisdictional boundaries;4) a logical extension of the calendar system;5) versatile, and facilitating quantitative studies by providing 46 suitable time slices of equal duration in the preparation of certain maps, sections, and graphs tracking the evolution of the geospheres for all of geologic history;6) applicable beyond Earth; and7) helpful in enhancing communication with non-geologists by obviating a series of complex names of units, and by taking advantage of the early-acquired ability to count.

Precambrian chronologic data span most of geologic time and are dominantly numeric, so why not also utilize a numerical classification and a matching ordinal nomenclature? Astronomers already employ light-year and parsec units for large distances, so it is entirely appropriate to adopt a scale for correspondingly long geologic and astronomic time intervals.

References:

Cowie, J.W., Ziegler, W., and Remane, J., 1989, Stratigraphic Commission accelerates progress, 1984 to 1989. Episodes, v. 12 (2), p. 79-83.Gove, P.B. (Editor-in-chief), 1986, Webster’s third new international dictionary of the English language, unabridged. Springfield, MA, Merriam-Webster Inc., 2663 p.Hofmann, H.J., 1990, Precambrian time units and nomenclature - the geon concept: Geology, v. 18, p. 340-341.Hofmann, H.J., 1992, New Precambrian time scale: comments. Episodes, v. 15 (2), p. 122-123.Hofmann, H.J., 1999, Geons and geons. Geology, v. 27, p. 855-856.Plumb, K.A., 1991, New Precambrian time scale. Episodes, v. 14, p. 139-140.Plumb, K.A., 1992, New Precambrian time scale: reply. Episodes, v. 15 (2), p. 124-125.

Concepts of time

•

Period, duration•

Point, occasion, event

• Tempo

• Irreversibility

Some applications

seconds

10

104

5

km

km

103 km

102 km

10 km

1 km

102101

100 m

10 m

1 m106104 108 1010 10141012 1016

geonhour day year Masec min ka Ga

Organisms

Gla

ciers

s

Mounta

in b

lte

Sed. basi

ns

As

robl

ms

t

ee

Use a universal calendar system with numerical units appropriately large to encompass major geological developments (basin formation, orogenic belts,

evolution, etc.). A convenient measure is a unit of 100 million years.

Why use the Geon concept?

Geons for the Precambrian!

It is numerical, direct, and simpleIt is easy to learn, remember, and applyIt is necessary to learn only 1 wordIt transcends language barriersIt is geopolitically neutralIt is a logical extension of the calendar systemIt provides time slices of equal durationIt is versatile and facilitates quantitative studiesIt is applicable beyond EarthIt is helpful in communicating with non-geologists

Precambrian chronologic data are dominantly numeric.

Then, why not utilize chronometric divisions with a corresponding numeric nomenclature?

Astronomers use light-year and parsec for large distances; it thus is appropriate to have a name for long time intervals

Clocks

Universal time (UT): Earth’s rotation with respect to Sun solar (synodic) day = 24h = 86,400s

Ephemeris time: Motion with respect to distant star sidereal day = 23h 56.1m = 86,164s

Atomic time:133 emission frequency of Cs 9,192,631,770/s

21

18

6

www.eps.mcgill.ca/~hofmann/geonscale.html

Terminal Proteroz. (Vendian/ Ediac.)

Cryogenian

Tonian

Stenian

Ectasian

Calymmian

Statherian

Orosirian

Rhyacian

Siderian

CENOZOIC

MESOZOIC

PALEOZOIC

NEOPROTEROZOIC

MESOPROTEROZOIC

PALEOPROTEROZOIC

NEOARCHEAN

PHANERO-ZOIC

PROTEROZOIC

ARCHEAN

CR

YP

TO

ZO

IC

(PR

EC

AM

BR

IAN

)

TIMEmill ions of years

HADEAN

EON ERA

Oldest invertebrates

Oldest dated terrestrial rocks

Oldest dated terrestrial minerals

Oldest microfossils, stromatolites

Oldest carbonate platforms

Oldest cyanobacterial biomarkers

Glaciations

Martian dubiofossils (ALH84001)

Oldest macrofossilsSudbury astrobleme

(Grypania)

4000

3000

2000

2500

1600

1000

~543

250

65

Ma

MESOARCHEAN

PALEOARCHEAN

EOARCHEAN

3600

2800

3200

Dinosaur extinction, oldest primates

Permian extinctionOldest repti les

Oldest birds, mammals, angiosperms

Cambrian explosion

Oldest chemofossils

Origin of Earth; oldest meteorites

Selected benchmarks

Oldest red algae

Oldest eucaryotic biomarkers

Oldest f ishes

Oldest amphibians

Oldest green algae

0 CretaceousJurassicTriassicPermianCarboniferousDevonianSilurianOrdovicianCambrian

NeogenePaleogene

Period,System

1000

GEON

(after Hofmann, 1990, 1992; 2000 - Geolog, v. 29, pt. 1, p. 18 )

Geologic scale - geon scale

Preston E. Cloud, Jr.1912-1991

Opinion

Rivers, 1997, Prec. Res. 86:117-154

17

26

10

Condie, 1997, Plate Tectonics and Crustal Evolution

Geon map units(after Hofmann, 1990, 1992)

Phanerozoic

Proterozoic

Archean

GEON

Geon map units and gaps

GEON HIATUS

Phanerozoic

Proterozoic

Archean

Phanerozoic

Proterozoic

Archean

40 00

30 00

20 00

0123456789

101112131415161718192021222324

2625

27282930313233343536373839404142434445

0

10 00

GEONMa Time-rock

1

34

11-10

12

161718

20-19

29-26

5

39

HJH 03

Geon Scale

TIMEmill ions

of years

Ga

LUNAR TIME SCALE MARTIAN TIME SCALE

HJH 03

Selected events Selected eventsPeriod,System GEON

ALH84001dubiofossils

ALH84001impact

ALH84001pyroxenite

4.1

3.9

3.2

1.1

Copernican

Eratosthenian

Late

Late

Early

Early

Early

Late

Middle

Middle

Imbrian

Nectarian

Pre-Nectarian

Copernicus

Tycho

? Eratosthenes

Major basins(CrisiumSerenitatisTranquilitatisetc.)

Imbrium Basin

Imbrium Lavas

Orientale Basin

(Murray et al., 1981) (Cattermole, 1992)

Hesperian

Amazonian

Noachian

4000

3000

2000

1000

0123456789

101112131415161718192021222324

2625

27282930313233343536373839404142434445

0

Time + rocks

SCALES

binary

nominal

ordinal

interval

ratio

EXAMPLE

limit

stratigraphic unit

stratigraphic succession

geochronometry

absolute zero

evolution

event

-10 -5 0

Carbonif. Cret.

Tertiary Quat.

pre- post-

0

Time

SCALES ASPECTS

binary

nominal

ordinal

interval

ratio

instant, event

age, quality

chronologic

duration, arbitrary zero

absolute zero (no -ve)

evolution, change

-10 -5 0

0

present

1 2 3 4

past future

infancy old age

Cambrian

TPS (Ediacaran)

Silurian

Ordovician

Carboniferous

Devonian

Triassic

Permian

L. Cretaceous

Jurassic

Neogene, Paleogene

U. Cretaceous

Cambrian

TPS (Ediacaran)

Silurian

Ordovician

Carboniferous

Devonian

Triassic

Permian

L. Cretaceous

Jurassic

Neogene, Paleogene,

U. Cretaceous

Comparing Phanerozoic system and geon boundaries

Period

0

1

2

3

4

5

Geon

0

1

2

3

4

5

GeonAge*

1.1

5.7

0

10

10

10

* Ma

1.1

5.7

0

10

10

10

Ma

* after Okulitch 1995, GSC Open File 3040

98.9 Ma

205.7 Ma

300 Ma

410 Ma

510 Ma

590 Ma

0 Ma

0123456789

101112131415161718192021222324

2625

27282930313233343536373839404142434445

Complex nomenclature

GOLDICH, 1968(Can. J. Earth Sci. 5:715-724)

Scheme based onequal time intervals,

but with complexalphanumeric nomenclature:

Greek letter units ascendingwith increasing age;

numbered units decreasingwith increasing age

GOLDICH, 1968(Can. J. Earth Sci. 5:715-724)

Scheme based onequal time intervals,

but with complexalphanumeric nomenclature:

Greek letter units ascendingwith increasing age;

numbered units decreasingwith increasing age

4321

Comparisons

100 a = 1 a = 1 year101 a = 1 decade102 a = 1 century103 a = 1 ka = 1 milennium106 a = 1 Ma = 1 megennium108 a = 1 geon109 a = 1 Ga = 1 gigennium

Numerical nomenclature

Units of 108 years previously considered

100 my, Ma - current geological literature(i nien) - Chinese geological literature

megacentury - A.F. Trendall, 1966becquerel - P.F. Hoffman, unpublishedgeocentury - P.E. Cloud, 1988geon - H.J. Hofmann, 1990

PRIMITIVE POZOIC

ROT

PROZOCI PO IC

HY ZO IC

EOZO

ARCHAEOZOIC

HURONI NAALGONKIAN

AGNOZ I

TO O C

GE

OG

EN

ICP

RIS

CO

AN

CRYPTOZOIC

COLLOZOIC

AZOIC

EAR Y PR CAMBRIAN

L E

MIDDLE PRECAMBRIAN LATE PRECAMBRIAN

PROTEROZOIC

EOMORPHIC

EPEIROPHYTIC

SIC

THALAS OPHYT

HA

DE

AN

EOBIOTICPROGONIC

PROGONOZOIC

LIPOZOIC

ARCEAH

N

RIPHEAN VENDIAN APHEBIAN HELIKIAN HADRYNIAN

PROTERYTI

OPHC

KEEWATIN

Terminology jungleth(after Hofmann, 1972, Int. Geol. Cong., 24 Sess., Proc. Sect. 1, p. 20-30)

HJH 00

Geon 5

Geons18-16

Geons11-10

Geon 3

Geon 2

Graphic representation of record

fit time to rock sequence

Thickness

Spatial section

fit rocks into time scale

Time

Time section

fit rocks into time scale

Time

Time section

Concepts

Rocks + gapsgaps

A B C D E F G H I J K L M N O P Q R S

Chronostrat.record

Sections

incomplete, discontinuousregionalregional

continuous, uniformuniversaluniversal

TimeTime

bins

Age distribution of continental crust