Geological Eons, Eras, Periods and Epochs, and How Fossils Are Used

Chart of major geological eons, eras, periods, epochs and events. How fossils are used by scientists to determine its relationship with other specimens, with objective to un-ravel evolutionary patterns and origins.

Index fossils are sometimes used by Geologists to determine stratigraphic data about Earth's surface. This is true in the case of spores and pollen grains, the reproductive materials found in plants. By doing so provides the palyntologist means to determine relative age and position of rock, containing the spores. When studying drill cores, this kind of information can be useful to miners searching for fossil fuels.

Palynologists have used index fossils for practical applications, including understanding relationship between major groups of plants, specifically, gymnosperms and angiosperms.
A good index fossil is considered to be one that is easily identifiable, with wide horizontal distribution, and vertical range of approximately one million years. Traditionally, due to scarcity and difficulty in identification, plant megafossils were rarely used as index fossils. Though possessing wide geographical distribution in various sedimentary rocks, the vertical range spans millions of years. Assemblages of megafossils used as indices (or, indexes), accompanied by palynological information, scientists have been able to characterize restrictive stratigraphic units in rock units containing megafossils.

EON

ERA

PERIOD

EPOCH

Characteristic organisms and major geological events

Duration in millions of years

Began (m.y.a.)

Phanerozoic Eon

C
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N
O
Z
O
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C

E
R
A

QUARTERNARY PERIOD

Quarternary

HOLOCENE EPOCH

Last 5,000 years

0-10,000 years ago

PLEISTO-
CENE EPOCH

2.5 million years

10,000 to 1.6 million years ago

TERTIARY PERIOD

Late Tertiary
Late Tertiary
Middle Tertiary
Middle Tertiary
Early Tertiary
Early Tertiary
K T Times
KT Times

PLIOCENE EPOCH

4.5 million years

2.5-7 million years ago

MIOCENE EPOCH

19 million years

7-26 million years ago

OLIGOCENE EPOCH

12 million years

26-38 million years ago

EOCENE EPOCH

16 million years duration

38-54 million years ago

PALEOCENE EPOCH

11 million years duration

54-65 million years ago

M
E
S
O
Z
O
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C

E
R
A

CRETACEOUS PERIOD

Later Cretaceous
Later Cretaceous
Early Cretaceous
Early Cretaceous

UPPER
Maastrichtian
Campanian
Santonian
Coniacian
Turonian
Cenomanian

76 million years duration

65-141 million years ago

LOWER
Albian
Aptian
Barremian
Hauterivian
Valanginian
Berriasian

JURASSIC PERIOD

Jurassic

UPPER
Tithonian
Kimmeridgian
Oxfordian

54 million years duration

141-195 million years ago

MIDDLE
Callovian
Bathonian
Bajocian
Aalenian

LOWER
Toarcian
Pliensbachian
Sinemurian
Hettangian

TRIASSIC PERIOD

Triassic

UPPER
Rhaetian
Norian
Carnian

30 million years duration

208-245 million years ago

MIDDLE
Ladinian
Anisian

LOWER (Scythian)
Olenekian
Induan

P
A
L
E
O
Z
O
I
C

E
R
A

PERMIAN PERIOD

Permian

UPPER
Lopingian
- Changhsingian
- Wuchiapingian


MIDDLE
Guadalupian
- Capitanian
- Wordian
- Roadian

55 million years duration

245-280 million years ago

LOWER
Cisuralian
- Kungurian
- Artinskian
- Sakmarian
- Asselian

C
A
R
B
O
N
I
F
E
R
O
U
S

PENNSYLVANIAN

UPPER
Kasimovian | Gzhelian

45 million years duration

280-325 million years ago

MIDDLE
Moscovian

LOWER
Bashkirian

MISSISSIPPIAN

Carboniferous
Carboniferous

UPPER
Serpukhovian
MIDDLE
Vis?an

20 million years duration

286-360 million years ago

LOWER
Tournaisian

DEVONIAN PERIOD

Devonian

UPPER
Fammenian | Fransnian

50 million years duration

360-408 million years ago

MIDDLE
Givetian | Eifelian

LOWER
Praghian | Lockhovian

SILURIAN PERIOD

Ordovician

UPPER
Pridolian | Ludlovian

40 million years duration

408-438 million years ago

LOWER
Wenlockian | Llandoverian

ORDOVICIAN PERIOD

Ordovician

UPPER
Ashgillian | Caradocian


MIDDLE
Llandeilian | Llanvirnian

65 million years duration

438-505 million years ago

LOWER
Arenigian | Tremadocian

CAMBRIAN PERIOD

Late Cambrian
Late Cambrian
Early Cambrian
Early Cambrian

UPPER
Furongian

70 million years duration

505-540 million years ago

MIDDLE
* table below

LOWER
* table below

Pre Cambrian

P
R
O
T
E
R
O
Z
O
I
C

E
R
A

VENDIAN PERIOD

vendian

--

540-650 million years ago

PRE-VENDIAN PERIOD

650-2,500 million years ago

ARCHAEAN
3.8 to 2.5 billion years ago
The atmosphere of Earth was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other toxic gases. During this time, the Earth's crust cooled enough that rocks and continental plates began to form. Early in the Archaean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. All life during the more than one billion years of the Archaean was bacterial, stromatolites, colonies of photosynthetic bacteria which have been found as fossils in Early Archaean rocks of South Africa and Western Australia. Stromatolites increased in abundance throughout the Archaean, but began to decline during the Proterozoic.

2,500-3800 million years ago

HADEAN
4.5 to 3.8 billion years ago
Hadean time is not a geological period as such. During Hadean time, the Solar System was forming. Sometime during the first 800 million or so years of its history, the surface of the Earth changed from liquid to solid. Once solid rock formed on the Earth, its geological history began. This most likely happened prior to 3.8 billion years, but hard evidence for this is lacking. Erosion and plate tectonics has probably destroyed all of the solid rocks that were older than 3.8 billion years.

3,800-4,600 million years ago

CAMBRIAN SUBDIVISIONS
Cambrian is divided into three epochs ? the Early Cambrian (Lower Cambrian, Caerfai or Waucoban), Middle Cambrian (St Davids or Albertian) and Furongian (a.k.a. Late/Upper Cambrian, Merioneth or Croixan). Each of the epochs are divided into two faunal stages. Only one, Paibian has been recognized by the International Commission on Stratigraphy. Others are still unnamed. However, the Cambrian is divided into several regional faunal stages.
Source: Answers.com - Cambrian Subdivisions

  Chinese North American Russian-Kazakhian Australian Regional
Furongian   Ibexian Ayusokkanian Idamean Dolgellian
  Sunwaptan Sakian Mindyallan Festiniogian
  Steptoan Aksayan Payntonian Maentwrogian
  Marjuman Batyrbayan    
Middle Cambrian Maozhangian Mayan Boomerangian  
Zuzhuangian Delamaran Amgan Undillian  
Zhungxian     Florian  
      Templetonian  
  Dyeran   Ordian  
Early Cambrian Longwangmioan Toyonian Lenian
Changlangpuan Montezuman Botomian    
Qungzusian   Atdabanian    
Meishuchuan   Tommotian    
    Nemakit-Daldynian    

Extant organisms in their structure and distribution, reflect the composition of their environments. We assume extinct organisms also adapted to their environment in the same way. If this assumption is true, then it is possible to determine seasonal variations using growth rings from petrified wood, including paleo-environmental availability of water and temperature changes. Fossilized wood which reflects lack of growth rings, indicate a continuous supply of water and uniform temperature, just as thickened cuticles and sunken stomata of fossilized leaves indicate a lack of water, while roots and spongy stem tissue suggest a swampy or aquatic paleo-environment. With such information extracted from morphology and anatomy of fossil plants, provides in part, the basis for paleoecology and paleoclimatology. Further studies are taken into consideration, such as those on sedimentary materials which naturally occur with the fossils and, how the fossil became preserved, all play into better understanding the paleoenvironment. Specialists caution however, conclusions should never be based entirely upon extant organisms and how they interact with present environments. What we observe occuring today, is not necessarily the key to the past. (Paleobotany and the Evolution of Plants, Stewart and Rothwell, 1993; DiMichele & Wing, 1987.)

Paleofloristics, which specializes in assemblages of fossil plants, provides insight into Earth's restricted and widescale climate. On the worldwide scale, such studies have provided scientists with insight into plate tectonics and continental drift. These studies can also provide further insight into plant distribution, population, migration and significant changes in early environments. Studies on succession of plants in the geological column have became popular among paleoecologists, and also useful in studies on extant organisms and plant successions in natural history.

Successional changes in organisms throughout natural history are the basis of studies related to the evolution of life. Most paleontologists focus more on relative stratigraphic positioning of fossils, than absolute ages. It remains more important to most in the field, to determine how a fossil relates to other specimen with objective to un-ravel evolutionary patterns and origins.

REFERENCES
Bringing Fossils to Life, An Introduction to Paleobiology, McGraw Hill Publishers, Donald R. Prothero

PaleobotanyPaleobotany and the Evolution of Plants, by Cambridge University Press; 2 edition, Wilson N. Stewart, Gar W. Rothwell

Prehistoric WorldAtlas of the Prehistoric World, by Discovery Channel Books, Douglas Palmer

Kingfisher Illustrated Dinosaur Encyclopedia, Kingfisher Publishers, David Burnie

FURTHER SUGGESTED READING
Adrienne Mayor's books
1) The First Fossil Hunters (Princeton 2000) explains how ancient Greek and Roman discoveries of mysterious petrifed bones of extinct dinosaurs and mastodons led to myths about griffins, giants, and monsters. Watch for "Ancient Monster Hunters" on the History Channel.
2) Fossil Legends of the First Americans (Princeton 2005) gathers exciting Native American discoveries and myths about fossils, from tiny shells to enormous dinosaur bones, with stories from more than 45 different tribes, beginning with the Aztecs & Incas.

Stephen Meyer's article, "Are Dinosaurs Mentioned in the Bible?"

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