| Quaternary Period | ||
|---|---|---|
| Holocene (Recent) | began 10,000 yrs ago (0.01 Ma) | |
| Pleistocene | began 1.8 Ma | |
| Tertiary Period | ||
| Pliocene | began 5 Ma | Neogene |
| Miocene | began 24 Ma | |
| Oligocene | began 37 Ma | Paleogene |
| Eocene | began 58 Ma | |
| Paleocene | began 65 Ma | |
Pleist = most |
Pleion = more
Meion = less
Oligos = few
Eos = dawn
Paleo = ancient |
|
|
| Leaf of Acer sp. (maple) Fernbank Museum of Natural History, Atlanta, GA Temporary exhibit on Chinese Dinosaurs |
|
| Unidentified flower Fernbank Museum of Natural History, Atlanta, GA Temporary exhibit on Chinese Dinosaurs |
Ratio of Oxygen 18 to Oxygen 16
measure ratios in foram shells
Lighter isotopes (O-16) accumulate in glacial ICE. Why?
During evaporation, lighter isotopes are concentrated in the water vapor in the air. This moves through the hydrologic cycle and later falls as rain or SNOW. The snow accumulates to form glaciers.
As a result, O-16 becomes trapped in glacial ice, and excess O-18 is left in the oceans, (did not evaporate).
Hence, as temperatures drop, air becomes drier, evaporation increases, and the percentage of O-18 in seawater (and in foram shells) INCREASES.
Foram shells rich in O-18 = COLD & DRY.
Foram shells richer in O-16 = WARM & WET.
Results?
Ice age is characterized by many glacial expansions separated by warmer interglacial intervals.
Names of the glacial and interglacial stages in North America:
Wisconsinan glacial stage (maximum 10,000 to 35,000 years ago; ended 10,000 to 15,000 years ago)
Sangamon interglacial or glacial minimum (about 125,000 years ago)
Illinoian glacial stage (about 500,000 years ago)
Yarmouth interglacial
Kansan glacial stage (about 1.4 million to 900,000 years ago)
Aftonian interglacial
Nebraskan glacial stage (about 2 million years ago)
The climatic cyclicity of the Ice Ages has not ended!
Click here to see US relief map from Johns Hopkins University Applied Physics Lab.
Click here for Ice Age exhibit from Illinois State Museum. Includes a video of retreating glaciers and fossil photographs.
Rivers flowed across what is now the continental shelf
(continental
shelf was above sea level during glaciations);
land bridges
across Bering Sea, between Australia and Indonesia;
led to
migrations.
A large continental mass became
centered over a pole.
Polar areas were cut off from warming by
tropical waters.
Same situation existed during Ordovician and
Permian glaciations.
Changes in distance and angular relationships between Earth and Sun due to periodic fluctuations in Earth's orbit.
92,500 year cycles approximate periodicity of oxygen isotope cycles in foraminifera shells from deep sea cores. (see Levin p. 539- 540)
Many smaller-scale cycles also occur:
41,000 year cycles of changing inclination of the Earth's axis
22,000-year cycles (precession of equinoxes due to wobble of Earth's axis)
ASTRONOMICAL CONTROL OF GLACIAL CYCLES.
 |
Sydney, Australia |
Mammals were initially small and generalized.
Rapid explosive adaptive radiation of mammals in Early Cenozoic.
Within only about 12 million years, mammals as diverse as bats (small, flying) and whales (large, swimming) had appeared, descended from the ancestral shrew-like (rat-like) mammalian ancestors.
Increase in variety of mammals in Eocene.
Number of families doubled.
Early
members of elephant family appeared.
Evolution of the horse from size of a small dog at end of Paleocene (Hyracotherium or Eohippus - the "dawn horse").
Mammals increased in size.
Oligocene: Rhino-like Titanotheres.
Largest land mammal of all time (Indrichotherium)
Mammoths and mastodons -
Mammoths are taller than mastodons, with high skullls. Also have more complex molars with ridges for grinding. Mammoths appeared in Africa 5 million years ago, migrated to the Northern Hemisphere, and became extinct about 10,000 years ago. Mastodons appeared 20 million years ago, and probably gave rise to the mammoths. Mammoths gave rise to modern elephants.
| Wooly mammoth. 16 ft tall. Largest ever found. 34,000 years old. From a coal mine in China. Note that the tusks on the skeleton are replicas. The actual fossil tusks are too heavy to mount and are displayed on the floor beside the mammoth. Fernbank Museum of Natural History, Atlanta, GA.
|
| Mastodont with calf - Diorama Lived in the northeastern US about 12,000 years ago New York State Museum, Albany, NY |
Click here to view picture of mastodon, Mammut americanum.
Click here to see mastodon in its habitat in the Midwest U.S. 16,000 years ago. Both pictures are from a mural by R. G. Larson in the Illinois State Museum.
| Wooly rhino. Remains have been found in ice and oil-saturated soil, which preserved the hair of these Ice Age Mammals. Fernbank Museum of Natural History
|
| Wooly rhinos in matrix as found. Fernbank Museum of Natural History, Atlanta, GA
|
| Cast of Platybelodon, commonly known as "Shovel Tusker". Height at shoulder =2.8 m. Early middle Miocene (15 million years old). From northwestern China. Inhabited swampy areas. Browsing herbivore. Fernbank Museum of Natural History Atlanta, GA.
|
| Diatryma, The Eocene's Big Bird Smithsonian Institution, Museum of Natural History, Washington, D.C. |
Tremendous adaptive radiations in these groups.
Decline of odd-toed ungulates (horses, tapirs, rhinos)
Expansion of even-toed ungulates (cloven hoof) (deer, cows, sheep, goats, pigs, bison, camels, etc.)
Diversification of herbivores led to rise in new carnivores.
Homo erectus was a tool maker.
|
| Smithsonian Institution, Museum of Natural History, Washington, DC |
 |
| Smithsonian Institution, Museum of Natural History, Washington, DC |
Return to Geology 102 Home Page
Return to Georgia Geoscience On-line
This page created by Pamela J. W. Gore
DeKalb College, Clarkston, GA
Page created on November 14, 1995
Modified November 25, 1996
Last modified November 12, 1997
