Late Cenozoic Ice Age

  1. ^ a b In standard nomenclature the Pleistocene Epoch lasts from 2.58 Ma to 11.7 ka and the Holocene epoch lasts from 11.7 ka to present. However, it is disputed whether these should in fact be treated separately, or whether the "Holocene" is in fact merely a Pleistocene interglacial.[2][3] See below for details.
  2. ^ The Anthropocene is a proposed epoch which seeks to recognize humanity's impact on the natural world. It has various proposed start dates and lasts until the present.

The Late Cenozoic Ice Age,[5][6] or Antarctic Glaciation[7][8] began 33.9 million years ago at the Eocene-Oligocene Boundary and is ongoing.[5] It is Earth's current ice age or icehouse period. Its beginning is marked by the formation of the Antarctic ice sheets.[9] The Late Cenozoic Ice Age gets its name due to the fact that it covers roughly the last half of Cenozoic era so far.

Six million years after the start of the Late Cenozoic Ice Age, the East Antarctic Ice Sheet had formed, and 14 million years ago it had reached its current extent. It has persisted to the current time.[10]

In the last three million years, glaciations have spread to the northern hemisphere. It commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago)[11] During the Pleistocene Epoch (starting 2.58 Ma ago), the Pleistocene Glaciation developed with decreasing mean temperatures and increasing amplitudes between glacials and interglacials. During the glacial periods of the Pleistocene, large areas of northern North America and northern Eurasia have been covered by ice sheets.

All palaeotemps
Neko1(js)
Neko Harbour, Antarctica circa 2000
Late Cenozoic Ice Age
33.9 million years ago to present
Divisions within the current ice age
For divisions prior to 33.9 million years ago, see Geologic Time Scale
Period Epoch Age

P
a
l
e
o
g
e
n
e
Oligocene Epoch
33.9 to 23.03 Ma
(last epoch of the Paleogene Period)
Pyrotherium romeroi and Rhynchippus equinus, Oligocene of South America
Rupelian
33.9 to 27.82 Ma
Chattian
27.82 to 23.03 Ma
N
e
o
g
e
n
e

Miocene
23.03 to 5.333 Ma
Fauna of Miocene North America
Aquitanian
23.03 to 20.44 Ma
Burdigalian
20.44 to 15.97 Ma
Langhian
15.97 to 13.82 Ma
Serravallian
13.82 to 11.63 Ma
Tortonian
11.63 to 7.246 Ma
Messinian
7.246 to 5.333 Ma
Pliocene
5.333 to 2.58 Ma
Fauna of Pliocene North America
Zanclean
5.333 to 3.6 Ma
Piacenzian
3.6 to 2.58 Ma
Q
u
a
t
e
r
n
a
r
y
Pleistocene
2.58 Ma to 11.7 ka[1][a]
Columbian mammoth, Pleistocene North America
Gelasian
2.58 to 1.8 Ma
Calabrian
1.8 Ma to 781 ka[1][4]
Middle Pleistocene ("Chibanian")
("Ionian")
781 to 126 ka[1]
Upper/Late Pleistocene ("Tarantian")
126 to 11.7 ka[1]
Holocene
11.7 ka to present[1][a][b]
Egypt.Giza.Sphinx.02
Greenlandian
11.7 to 8.2 ka[1]
Northgrippian
8.2 to 4.2 ka[1]
Meghalayan
4.2 ka to present[1]

The Late Cenozoic Ice Age falls within the Cenozoic Era which started 66 million years ago. The Cenozoic Era is part of the Phanerozoic Eon which started 541 million years ago.

  1. ^ a b In standard nomenclature the Pleistocene Epoch lasts from 2.58 Ma to 11.7 ka and the Holocene epoch lasts from 11.7 ka to present. However, it is disputed whether these should in fact be treated separately, or whether the "Holocene" is in fact merely a Pleistocene interglacial.[2][3] See below for details.
  2. ^ The Anthropocene is a proposed epoch which seeks to recognize humanity's impact on the natural world. It has various proposed start dates and lasts until the present.

History of Discovery and Naming

German naturalist, Karl Friedrich Schimper coined the term Eiszeit meaning ice age in 1837. For a long time, the term only referred to glacial periods. At some point later, this developed into the concept that they were all part of a much longer ice age.

The concept that the earth is currently in an ice age that began around 30 million years ago can be dated back to at least 1966.[12]

As a geologic time period, the Late Cenozoic Ice Age was used at least as early as 1973.[13]

The Climate before the Polar Ice Caps

Washingtonia filifera in Palm Canyon
This type of vegetation grew in Antarctica during the Eocene Epoch - Photo taken at Palm Canyon, California, US in 2005

The last greenhouse period began 260 million years ago during the late Permian Period at the end of the Karoo Ice Age. It lasted all through the time of the non-avian dinosaurs during the Mesozoic Era, and ended 33.9 million years ago in the middle of the Cenozoic Era (the current Era). This greenhouse period lasted 226.1 million years.

The hottest part of the last greenhouse earth was the Late Paleocene - Early Eocene Torrid Age. This was a hothouse period that lasted from 65 to 55 million years ago. The hottest part of this torrid age was the Paleocene-Eocene Thermal Maximum, 55.5 million years ago. Average global temperatures were around 30 °C (86 °F),[14] which is about 15 °C (27 °F) warmer than present. This was only the second time that Earth reached this level of warmth since the Precambrian. The other time was during the Cambrian Period, which ran from 541 million years ago to 485.4 million years ago.

During the early Eocene, Australia[15] and South America[16] were connected to Antarctica.

53 million years ago during the Eocene Epoch, summer high temperatures in Antarctica were around 25 °C (77 °F).[15] Temperatures during winter were around 10 °C (50 °F).[15] It did not frost during the winter.[15] The climate was so warm that trees grew in Antarctica.[15] Arecaceae (palm trees) grew on the coastal lowlands, and Fagus (beech trees) and Pinophyta (conifers) grew on the hills just inland from the coast.[15]

Temperatures soon began to decrease as the methane levels in the atmosphere started to decline.[5]

As the global climate became cooler, the planet was seeing a decrease in forests, and an increase in savannas.[14] Animals were evolving to have a larger body size.[14]

Glaciation of the Southern Hemisphere

Antarktyda i Antarktyka
Antarctica from space on 21 September 2005

Australia drifted away from Antarctica forming the Tasmanian Passage, and South America drifted away from Antarctica forming the Drake Passage. This caused the formation of the Antarctic Circumpolar Current, a current of cold water surrounding Antarctica.[10] This current still exists today, and is a major reason for why Antarctica has such an exceptionally cold climate.[15]

The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate.[17][10] At this point CO2 levels had dropped to 750 ppm.[18] This was the beginning of the Late Cenozoic Ice Age. This was when the ice sheets reached the ocean,[19] the defining point.[20]

33 million years ago was the evolution of the thylacinid marsupial (Badjcinus).

The first balanids, cats, eucalypts, and pigs came about 30 million years ago. The brontothere and embrithopod mammals went extinct at this time.

At 29.2 million years ago, there were three ice caps in the high elevations of Antarctica.[10] One ice cap formed in the Dronning Maud Land.[10] Another ice cap formed in the Gamburtsev Mountain Range.[10] Another ice cap formed in the Transantarctic Mountains.[10] At this point, the ice caps weren't very big yet.[10] Most of Antarctica wasn't covered by ice.[10]

By 28.7 million years ago, the Gamburtsev ice cap was now much larger due to the colder climate.[10]

CO2 continued to fall and the climate continued to get colder.[10] At 28.1 million years ago, the Gamburtsev and Transantarctic ice caps merged into a main central ice cap.[10] At this point, ice was now covering a majority of the continent.[10]

28 million years ago was the time period in which the largest land mammal existed, the Paraceratherium.

The Dronning Maud ice cap merged with the main ice cap 27.9 million years ago.[10] This was the formation of the East Antarctic Ice Sheet.[10]

25 million years ago brought about the first deer. It also was the time period in which the largest flying bird existed, the Pelagornis sandersi.

Global refrigeration set in 22 million years ago.[9]

20 million years ago brought about the first bears, giraffes, giant anteaters, and hyenas. There was also an increase in the diversity of birds.

The first bovids, kangaroos, and mastodons came about 15 million years ago. This was the warmest part of the Late Cenozoic Ice Age, with average global temperatures around 18.4 °C (65.1 °F).[21] This is about 3.4 °C (6.2 °F) warmer than the 2013-2017 average. Atmospheric CO2 levels were around 700 ppm.[21] This time period was called the Mid-Miocene Climatic Optimum (MMCO).

By 14 million years ago, the Antarctic ice sheets were similar in size and volume to present times.[5] Glaciers were starting to form in the mountains of the Northern Hemisphere.[5]

The Great American Interchange occurred 9.5 million years ago. This was the migration of different land and freshwater animals between North and South America. During this time, armadillos, glyptodonts, ground sloths, hummingbirds, meridiungulates, opossums, and phorusrhacids migrated from South America to North America. Also, bears, deer, coaties, ferrets, horses, jaguars, otters, saber-toothed cats, skunks, and tapirs migrated from North America to South America.

The first hominin came about 6.5 million years ago. It was the Sahelanthropus.

The australopithecines became diverse six million years ago. The Mediterranean Sea was dry between 6 and 5 million years ago.[5]

Five million years ago brought about the first hippopotami and tree sloths. Elephants, zebras, and other grazing herbivores became more diverse. Lions, members of the genus Canis, and other large carnivores became more diverse. The burrowing rodents, birds, kangaroos, small carnivores, and vultures increase in size. There was a decrease in the number of perissodactyl mammals, and the nimravid carnivores went extinct.

The first mammoths came about 4.8 million years ago.

The evolution of the Australopithecus occurred four million years ago. This was also the time of the largest freshwater turtle, Stupendemys. The first modern elephants, gazelles, giraffes, lions, rhinoceros, and zebras came about at this time.

Between 3.6 and 3.4 million years ago, there was a sudden but brief warming period.[5]

Glaciation of the Northern Hemisphere

Arctic Sea Ice - September 2009 to March 2010 (4497233026)
Arctic sea ice from space on 6 March 2010

The glaciation of the Arctic in the Northern Hemisphere commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago).[11]

The evolution of the Paranthropus occurred 2.7 million years ago.

2.58 million years ago was the official start of the Quaternary glaciation, the current phase of the Late Cenozoic Ice Age. Throughout the Pleistocene, there have been glacial periods (cold periods with extended glaciation) and interglacial periods (warm periods with less glaciation).

The term stadial is another word for glacial period, and interstadial is another word for interglacial period.

The oscillation between glacial and interglacial periods is due to the Milankovitch cycles. These are cycles that have to do with Earth's axial tilt and orbital eccentricity.

Earth is currently tilted at 23.5 degrees. Over a 41,000 year cycle, the tilt oscillates between 22.1 and 24.5 degrees.[22] When the tilt is greater (high obliquity), the seasons are more extreme. During times when the tilt is less (low obliquity), the seasons are less extreme. Less tilt also means that the polar regions receive less light from the sun. This causes a colder global climate as ice sheets start to build up.[22]

The shape of Earth's orbit around the sun affects the Earth's climate. Over a 100,000 year cycle, Earth oscillates between having a circular orbit to having a more elliptical orbit.[22]

From 2.58 million years ago to about 1.73 million ± 50,000 years years ago, the degree of axial tilt was the main cause of glacial and interglacial periods.[22]

2.5 million years ago brought about the evolution of the earliest Smilodon species.

Homo habilis came about two million years ago. This was the first species of the genus Homo. Conifer trees became more diverse in the high latitudes. The ancestor of cattle evolved in India, the Bos primigenus (aurochs).

The extinction of the australopithecines occurred 1.7 million years ago.

The evolution of Homo antecessor occurred 1.2 million years ago. Paranthropus also became extinct.

Around 850,000 ± 50,000 years ago, the degree of orbital eccentricity became the main driver of glacial and interglacial periods rather than the degree of tilt, and this pattern continues to present-day.[22]

800,000 years ago, the short-faced bear (Arctodus simus) became abundant in North America.

The evolution of the Homo heidelbergensis happened 600,000 years ago.

The evolution of Neanderthals occurred 350,000 years ago.

300,000 years ago, Gigantopithicus went extinct.

250,000 years ago in Africa were the first anatomically modern humans.

Last Glacial Period

Snowbound Neanderthals
Neanderthals during the last glacial period.
Northern icesheet hg
Map of the Northern Hemisphere ice during the last glacial maximum.

The last glacial period began 115,000 years ago and ended 11,700 years ago. This time period saw the great advancement of polar ice sheets into the middle latitudes of the Northern Hemisphere.

Around 75,000 years ago was the eruption of the Toba Supervolcano at present-day Lake Toba, Sumatra, Indonesia. The eruption caused a world-wide volcanic winter that lasted six to ten years. It is possible that it may have even had a cooling effect on the climate that lasted for a thousand years.

There is a bottleneck in the human DNA, and it is believed to be a result of the Toba eruption. It is believed that the six to ten years of cold weather during the volcanic winter destroyed much of the food sources, and greatly reduced the human population.

50,000 years ago, Homo sapiens migrated out of Africa. They began replacing other Hominins in Asia. They also began replacing Neanderthals in Europe. However some of the Homo sapiens and Neanderthals interbred. Currently, persons of European descent are two to four percent Neanderthal. With the exception of this small amount of Neanderthal DNA that exists today, Neanderthals went extinct 30,000 years ago.

The last glacial maximum ran from 26,500 years ago to 20,000 years ago. Although different ice sheets reached maximum extent at somewhat different times, this was the time when ice sheets overall were at maximum extent.

According to Blue Marble 3000 (a video by the Zurich University of Applied Sciences), the average global temperature around 19,000 BCE (about 21,000 years ago) was 9.0 °C (48.2 °F).[23] This is about 6.0 °C (10.8 °F) colder than the 2013-2017 average.

The figures given by the Intergovernmental Panel On Climate Change (IPCC) estimate a slightly lower global temperature than the figures given by the Zurich University of Applied Sciences. However, these figures are not exact figures and are open more to interpretation. According to the IPCC, average global temperatures increased by 5.5 ± 1.5 °C (9.9 ± 2.7 °F) since the last glacial maximum, and the rate of warming was about 10 times slower than that of the 20th Century.[24] It appears that they are defining the present as sometime in the 19th Century for this case, but they do not specify exact years, or give a temperature for the present.

Berkeley Earth puts out a list of average global temperatures by year. If you average all of the years from 1850 to 1899, the average temperature comes out to 13.8 °C (56.9 °F).[25] When subtracting 5.5 ± 1.5 °C (9.9 ± 2.7 °F) from the 1850-1899 average, the average temperature for the last glacial maximum comes out to 8.3 ± 1.5 °C (47.0 ± 2.7 °F). This is about 6.7 ± 1.5 °C (12.1 ± 2.7 °F) colder than the 2013-2017 average. This figure is open to interpretation because the IPCC does not specify 1850-1899 as being the present, or give any exact set of years as being the present. It also does not state whether or not they agree with the figures given by Berkeley Earth.

According to the United States Geographical Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum.[26] The USGS also states that sea level was about 125 m (410 ft) lower than in present times (2012).[26] The volume of ice on Earth was around 17,000,000 mi3 (71,000,000 km3),[27] which is about 2.1 times Earth's current volume of ice.

The extinction of the woolly rhinoceros (Coelodonta antiquitus) occurred 15,000 years ago after the last glacial maximum.

Current Interglacial Period

Anna Ancher - Harvesters - Google Art Project
Agriculture and the rise of civilization came about during the current interglacial period.

The Earth is currently in an interglacial period which began 11,700 years ago. This is traditionally referred to as the Holocene epoch and is currently (as of 2018) recognized as such by the International Commission on Stratigraphy.[1] However, there is debate as to whether it is actually a separate epoch or merely an interglacial period within the Pleistocene epoch.[2][3] This period can also be referred to as the Flandrian interglacial or Flandrian stage.

According to Blue Marble 3000, the average global temperature at the beginning of the current interglacial period was around 12.9 °C (55.2 °F).[23]

Agriculture began 11,500 years ago.

Equidae, giant ground sloths, and short-faced bears became extinct 11,000 years ago.

The Smilodon became extinct 10,000 years ago, as well as the mainland species of the woolly mammoth.

The giant lemur went extinct 8,000 years ago.

Around 3,200 BCE (5,200 years ago) the first writing system was invented.[28] It was the cuneiform script used in Mesopotamia (present day Iraq).[28]

The last mammoths at Wrangel Island off the coast of Siberia went extinct around 3,700 years ago.[29]

According to Berkeley Earth's list of average global temperatures by year, the average global temperature for the 1850-1899 period was 13.8 °C (56.9 °F).[25] Because greenhouse gases have increased rapidly since the 19th century, the average global temperature was 15.0 °C (58.9 °F) for the 2013-2017 period.[25]

Being in an interglacial, there is less ice than there was during the last glacial period. However, the last glacial period was just one part of the ice age that still continues today. Even though Earth is in an interglacial, there is still more ice than times outside of ice ages. There are also currently ice sheets in the Northern Hemisphere, which means that there is more ice on Earth than there was during the first 31 million years of the Late Cenozoic Ice Age. During that time, only the Antarctic ice sheets existed. Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice according to the USGS.[26] The total volume of ice presently on Earth is about 33,000,000 km3 (8,000,000 mi3) (as of 2004).[30] The current sea level (as of 2009) is 70 m (230 ft) lower than it would be without the ice sheets of Antarctica and Greenland.[17]

See also

External links

  • Blue Marble 3000, an animation by Zurich University of Applied Sciences showing global ice sheets from 19,000 BCE to 3000 CE

References

  1. ^ a b c d e f g h i "2018 Geologic Time Scale". International Commission on Stratigraphy.
  2. ^ a b de Blij, Harm (2012-08-17). "Holocene Humanity". Why Geography Matters: More Than Ever. Oxford University Press. ISBN 9780199977253.
  3. ^ a b "Neogene HSU NHM". Humboldt State University.
  4. ^ "Calabrian Stage". Encyclopedia Britannica.
  5. ^ a b c d e f g University of Houston-Clear Lake - Disasters Class Notes - Chapter 12: Climate Change sce.uhcl.edu/Pitts/disastersclassnotes/chapter_12_Climate_Change.doc
  6. ^ National Academy of Sciences - The National Academies Press - Continental Glaciation through Geologic Times https://www.nap.edu/read/11798/chapter/8#80
  7. ^ Kvasov, D.D.; Verbitsky, M.Ya. (2017). "Causes of Antarctic Glaciation in the Cenozoic". Quaternary Research. 15: 1–17. doi:10.1016/0033-5894(81)90110-1.
  8. ^ Goldner, A.; Herold, N.; Huber, M. (2014). "Antarctic glaciation caused ocean circulation changes at the Eocene–Oligocene transition". Nature. 511 (7511): 574–577. doi:10.1038/nature13597. PMID 25079555.
  9. ^ a b "Continental Glaciation through Geologic Times". Climate in Earth History: Studies in Geophysics: 80. 1982. |chapter= ignored (help)
  10. ^ a b c d e f g h i j k l m n o Deconto, Robert M.; Pollard, David (2003). "Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric CO2". Nature. 421 (6920): 245–249. doi:10.1038/nature01290. PMID 12529638.
  11. ^ a b Bartoli, G; Sarnthein, M; Weinelt, M; Erlenkeuser, H; Garbe-Schönberg, D; Lea, D.W (2005). "Final closure of Panama and the onset of northern hemisphere glaciation". Earth and Planetary Science Letters. 237 (1–2): 33–44. doi:10.1016/j.epsl.2005.06.020.
  12. ^ The Stanford Daily - Stanford, California, United States - Man's Relation To Nature Topic Of Eiseley's Lecture - 1966 October 20.
  13. ^ Hughes, T. (1973). "Is the west Antarctic Ice Sheet disintegrating?". Journal of Geophysical Research. 78 (33): 7884–7910. doi:10.1029/JC078i033p07884.
  14. ^ a b c "The Eocene Epoch". University of California - Museum of Paleontology.
  15. ^ a b c d e f g "Ancient Climate Change Meant Antarctica Was Once Covered with Palm Trees". Smithsonian Magazine.
  16. ^ Houle, Alain (1999). "The origin of platyrrhines: An evaluation of the Antarctic scenario and the floating island model". American Journal of Physical Anthropology. 109 (4): 541–559. doi:10.1002/(SICI)1096-8644(199908)109:4<541::AID-AJPA9>3.0.CO;2-N.
  17. ^ a b Liu, Z.; Pagani, M.; Zinniker, D.; Deconto, R.; Huber, M.; Brinkhuis, H.; Shah, S. R.; Leckie, R. M.; Pearson, A. (2009). "Global Cooling During the Eocene-Oligocene Climate Transition" (PDF). Science. 323 (5918): 1187–1190. doi:10.1126/science.1166368. PMID 19251622. Lay summaryUniversity of Massachusetts (February 26, 2009).
  18. ^ "11". IsotopeGeochemistry - Unconventional Isotopes And Approaches (PDF). Cornell University. 2013.
  19. ^ "The Late Eocene Earth — Hothouse, Icehouse, and Impacts" (PDF). Geologic Society Of America.
  20. ^ "A human-induced hothouse climate?" (PDF). UMass Lowell.
  21. ^ a b "Simulation of the Middle Miocene Climate Optimum". University of Michigan.
  22. ^ a b c d e "Is An Ice Age Coming?". PBS Space Time. PBS Digital Studios. 2016-05-25.
  23. ^ a b "Blue Marble 3000 (animation)". YouTube. Zurich University of Applied Sciences. 2011-03-08.
  24. ^ "Climate Change 2007: Working Group I: The Physical Science Basis - Executive Summary". Intergovernmental Panel On Climate Change.
  25. ^ a b c "Land and Ocean Summary". Berkeley Earth.
  26. ^ a b c "Glacier and Landscape Change in Response to Changing Climate - Glaciers and Sea Level". United States Geological Survey.
  27. ^ HowStuffWorks - Evidence of the Ice Age https://history.howstuffworks.com/historical-events/ice-age1.htm
  28. ^ a b Schmandt-Besserat, Denise (2014-01-25). "The Evolution of Writing". University of Texas.
  29. ^ "How to Clone a Mammoth: The Science of De-Extinction" (PDF). Princeton University Press.
  30. ^ University of Kansas - Center for Remote Sensing of Ice Sheets http://nia.ecsu.edu/cerser/2004/041018ku/ku.htm
Azolla event

The Azolla event is a scenario hypothesized to have occurred in the middle Eocene epoch, around 49 million years ago, when blooms of the freshwater fern Azolla are thought to have happened in the Arctic Ocean. As they sank to the stagnant sea floor, they were incorporated into the sediment; the resulting draw-down of carbon dioxide has been speculated to have helped transform the planet from a "greenhouse Earth" state, hot enough for turtles and palm trees to prosper at the poles, to the current icehouse Earth known as the Late Cenozoic Ice Age.

Carbonate–silicate cycle

The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by metamorphism and volcanism. Carbon dioxide is removed from the atmosphere during burial of weathered minerals and returned to the atmosphere through volcanism. On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.However the rate of weathering is sensitive to factors that modulate how much land is exposed. These factors include sea level, topography, lithology, and vegetation changes. Furthermore, these geomorphic and chemical changes have worked in tandem with solar forcing, whether due to orbital changes or stellar evolution, to determine the global surface temperature. Additionally, the carbonate-silicate cycle has been considered a possible solution to the Faint young Sun paradox.

Cat gap

The cat gap is a period in the fossil record of approximately 25 to 18.5 million years ago in which there are few fossils of cats or cat-like species found in North America. The cause of the "cat gap" is disputed, but may have been caused by changes in the climate (global cooling), changes in the habitat and environmental ecosystem, the increasingly hypercarnivorous trend of the cats (especially the nimravids), volcanic activity, evolutionary changes in dental morphology of the Canidae species present in North America, or a periodicity of extinctions called van der Hammen cycles.

Cenozoic

The Cenozoic Era ( see-nə-ZOH-ik, -⁠noh-, SEN-ə-, SEN-oh-) meaning "new life", is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and extending from 66 million years ago to the present day. It is generally believed to have started on the day of the Cretaceous–Paleogene extinction event when an asteroid hit the earth.The Cenozoic is also known as the Age of Mammals, because the extinction of many groups allowed mammals to greatly diversify so that large mammals dominated the Earth. The continents also moved into their current positions during this era.

Early in the Cenozoic, following the K-Pg extinction event, most of the fauna was relatively small, and included small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. A group of avians known as the "terror birds" grew larger than the average human and were formidable predators. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's mammals.

The Earth's climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum.

Greenhouse and icehouse Earth

Throughout the history of the Earth, the planet's climate has been fluctuating between two dominant climate states: the greenhouse Earth and the icehouse Earth. These two climate states last for millions of years and should not be confused with glacial and interglacial periods, which occur only during an icehouse period and tend to last less than 1 million years. There are five known great glaciations in Earth's climate history; the main factors involved in changes of the paleoclimate are believed to be the concentration of atmospheric carbon dioxide, changes in the Earth's orbit, long-term changes in the solar constant, and oceanic and orogenic changes due to tectonic plate dynamics. Greenhouse and icehouse periods have profoundly shaped the evolution of life on Earth.

Ice age

An ice age is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and greenhouse periods, during which there are no glaciers on the planet. Earth is currently in the Quaternary glaciation, known in popular terminology as the Ice Age. Individual pulses of cold climate within an ice age are termed "glacial periods" (or, alternatively, "glacials", "glaciations", "glacial stages", "stadials", "stades", or colloquially, "ice ages"), and intermittent warm periods within an ice age are called "interglacials" or "interstadials", with both climatic pulses part of the Quaternary or other periods in Earth's history.In the terminology of glaciology, ice age implies the presence of extensive ice sheets in both northern and southern hemispheres. By this definition, we are in an interglacial period—the Holocene. The amount of heat trapping gases emitted into Earth's oceans and atmosphere are predicted to prevent the next glacial period, which otherwise would begin in around 50,000 years, and likely more glacial cycles.

Last Glacial Period

The Last Glacial Period (LGP) occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. This most recent glacial period is part of a larger pattern of glacial and interglacial periods known as the Quaternary glaciation extending from c. 2,588,000 years ago to present. The definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid-Cenozoic (Eocene–Oligocene extinction event). The term Late Cenozoic Ice Age is used to include this early phase.During this last glacial period there were alternating episodes of glacier advance and retreat. Within the last glacial period the Last Glacial Maximum was approximately 22,000 years ago. While the general pattern of global cooling and glacier advance was similar, local differences in the development of glacier advance and retreat make it difficult to compare the details from continent to continent (see picture of ice core data below for differences). Approximately 13,000 years ago, the Late Glacial Maximum began. The end of the Younger Dryas about 11,700 years ago marked the beginning of the Holocene geological epoch, which includes the Holocene glacial retreat.

From the point of view of human archaeology, the last glacial period falls in the Paleolithic and early Mesolithic periods. When the glaciation event started, Homo sapiens were confined to lower latitudes and used tools comparable to those used by Neanderthals in western and central Eurasia and by Denisovans and Homo erectus in Asia. Near the end of the event, Homo sapiens migrated into Eurasia and Australia. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived the last glacial period in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover.

Penultimate Glacial Period

The Penultimate Glacial Period (PGP) is the glacial period that occurred before the Last Glacial Period. It began ~194,000 years ago, and ended 135,000 years ago with the beginning of the Eemian interglacial. It roughly coincides with Marine Isotope Stage 6 (see Marine Isotope Stage) and the Illinoian Stage. The penultimate glacial period is one of a series of glacial and interglacial periods of the Quaternary Ice Age/Quaternary Glaciation. The Quaternary Ice Age began 2.58 million years ago and is ongoing. It began with the formation of the Arctic Ice Cap. The Quaternary Ice Age is part of an even longer ice age called the Late Cenozoic Ice Age. It began 33.9 million years ago and is also ongoing. It began with the formation of the Antarctic Ice Cap.Just like the Last Glacial Period, the penultimate glacial period has no name. The word penultimate means second to last.

The penultimate glacial period was at least the second glacial period that Neanderthals, Denisovans, and Homo sapiens experienced.

Penultimate Glacial Period was more severe than the Last Glacial Period.

Rocky Prairie

Rocky Prairie is a prairie that is about 90 kilometers (56 miles) southwest of Seattle, Washington, United States, and about 15 kilometers (10 miles) south of Washington's capital city of Olympia. It sits very close to the Millersylvania State Park, the community of Maytown, and the city of Tenino.

Old Highway 99 runs through Rocky Prairie. The part of the prairie west of the highway is called West Rocky Prairie. Both the west and east sides of the prairie have various plant and animal species. Many of the plant species are flowering plants. Both sides also have areas of Mima mounds (not to be confused with the Mima mounds at Mima Mounds Natural Area Preserve about 10.5 kilometers or 6.5 miles to the west).

Rocky Prairie is divided into several different properties. The two land owners west of Old Highway 99 are the Washington State Department of Fish and Wildlife and the Port of Tacoma. A major land owner east of Old Highway 99 is the Washington State Department of Natural Resources. There is also another property on the east side owned by Thurston County which has a gravel pit located on it. Some of the prairie on the east side is private property, and has pastures and houses on it.

In West Rocky Prairie, the property that belongs to the Washington State Department of Fish and Wildlife is called the West Rocky Prairie Wildlife Area. The size of the property is 810 acres (328 hectares). Part of the property is wooded, and part of it is in the prairie. The West Rocky Prairie Unit has over 300 acres (120 hectares) of woods, 360 acres (145 hectares) of wetlands, 40 acres (15 hectares) of Quercus garryana (Garry oak trees), and 300 acres (120 hectares) of Mima mounds.

Tasmanian Passage

Tasmanian Passage, also Tasmanian Gateway or Tasmanian Seaway, is the name of ocean waters

Australia and Antarctica.

It was formed from the separation of the two continental plates of Australia and Antarctica about 30 to 40 million years ago. The Tasman Passage connects the Indian Ocean with the Pacific Ocean south of Australia. The term comes from geology. The distance between the two continents is currently about 2,300 kilometers (1,400 miles).

Through the opening of the Drake Passage and the Tasmanian Passage, the Antarctic circumpolar current was able to form in the course of the Oligocene, replacing the circumpacial equatorial flow conditions of the Cretaceous. The emergence of the circumpolar current led to a thermal isolation of the Antarctic, since the exchange with equatorial warm waters was greatly reduced. As a result, the ice sheets of Antarctica formed and the Earth entered the Late Cenozoic Ice Age (the current ice age).

Timeline of glaciation

There have been five or six major ice ages in the history of Earth over the past 3 billion years.

The Late Cenozoic Ice Age began 34 million years ago, its latest phase being the Quaternary glaciation, in progress since 2.58 million years ago.

Within ice ages, there exist periods of more severe glacial conditions and more temperate referred to as glacial periods and interglacial periods, respectively. The Earth is currently in such an interglacial period of the Quaternary glaciation, with the last glacial period of the Quaternary having ended approximately 11,700 years ago, the current interglacial being known as the Holocene epoch.

Based on climate proxies, paleoclimatologists study the different climate states originating from glaciation.

Vashon Glaciation

The Vashon Glaciation, Vashon Stadial or Vashon Stade is a local term for the most recent period of very cold climate in which during its peak, glaciers covered the entire Puget Sound and Strait of Juan de Fuca as well as present day Seattle, Tacoma, Olympia and other surrounding areas in the western part of present-day Washington (state) of the United States of America. This occurred during a cold period around the world known as the last glacial period. This was the most recent cold period of the Pleistocene Ice Age. The Pleistocene Glaciation is the ice age that the planet is currently in and has been in for the last 2.58 million years. It is the time period in which the arctic ice sheets have existed. The Pleistocene Ice Age is part of an even longer ice age called the Late Cenozoic Ice Age, which began 33.9 million years ago and is ongoing. It is the time period in which the Antarctic ice cap has existed.

The Vashon Glaciation lasted from about 19,000 – 16,000 BP (Before Present – present defined as January 1, 1950 for this scale). The Cordilleran Ice Sheet was an ice sheet that covered present-day southern Alaska and parts of western Canada. During the Vashon Glaciation, the Cordilleran Ice Sheet advanced into the Puget Sound region out of present-day British Columbia.

The Cordilleran, Laurentide, Innuitian, and the currently existing Greenland Ice Sheet all made up the North American ice sheet complex, which covered present day Canada and much of the northern U.S. This cold glaciated time for North America was called the Wisconsin glaciation. The Fraser Glaciation began when the Cordilleran Ice Sheet advanced from the mountains of British Columbia.

Quaternary /
Late Cenozoic
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Cryogenian
Paleoproterozoic
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