Download - climate change through geological era
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CLIMATE CHANGE THROUGH GEOLOGICAL
ERA
DEEPCHAND VDEPARTMENT OF GEOLOGY
UNIVERSITY OF KERALATRIVANDRUM
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GEOLOGICAL TIME SCALE
• To place all the scattered pages of earth history in their proper
chronological order is by no means an easy task (Holmes,
1965)
• Ordering these scattered and pages, and understanding the
physical, chemical and biological processes that acted on
them since Earth appeared and solidified, requires a detailed
and accurate time scale.
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Fig 1
Geological time scale
Source :http://paleo.cortland.edu/tutorial/Timescale/timescale.htm
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Fig 2 and 3
Geological time with evolution of life
Source: https://www.quora.com/Is-the-geologic-time-scale-useful
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PALEOCLIMATOLOGY
•“Paleoclimatology, the study of climates of the past, is closely
related to geology, to climatology, and to meteorology, and it
touches upon many branches of natural sciences”
•The climatic evidences from fossils and rocks used to
reconstruct the paleoclimates.
•The principles of Physics, Geophysics, Astronomy, and
meteorology also used in paleoclimate reconstruct.
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PIONEERS OF PALEOCLIMATOLOGY
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TO UNDERSTAND THE RANGE AND
EFFECTS OF FUTURE CLIMATE
• We must rely on instrumental records at most a few hundred
years long. longer geologic records that extend back over
millions of years.
• The reconstructed records of paleoclimate provide important
insights into potential rates and magnitudes of change, warm
and cold extremes that lasted for 1000s of years, and large
changes in sea level.
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HOW TO STUDY PALEOCLIMATES
•Study of Earth's climate during the entire history of the Earth.
•Uses geologic and biologic evidence climate proxies
preserved insediments
rocks
tree rings
corals,
ice sheets and other climate archives
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HOW IS PAST CLIMATE RECONSTRUCTED?
•From a variety of geologic and biologic archives that preserve
climate proxies(evidence of past climate and environment)
Archives..
• Terrestrial or aquatic sediments,
• Ice cores from glaciers and ice sheets,
• Tree rings,
• Corals
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HOW IS PAST CLIMATE RECONSTRUCTED?
These archives contain climate proxies, which are physical, chemical, or biological
features that provide information on past climate and environment
• Sea level,
• Air and ocean temperature,
• Atmospheric composition,
• Precipitation
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Fig 5
Different archives and proxies used in climate change studies.
Source : www.USGSpaleoclimateHome.com
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HOW DO WE KNOW THE TIME PERIOD
REPRESENTED BY A PALEOCLIMATE
RECORD?• ages of the archives and proxies
Analytical techniques DATING
Nature of radioactive isotopes (e.g., radiocarbon,
uranium-thorium) present in sample material.
Biostratigraphy
Which uses the fossil assemblages contained within a
sample to estimate its age
Ice core Estimate the amount of time of a sample
material (boulder) deposited by an ice sheet or shoreline
has been exposed on the Earth's surface to cosmic rays.
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Counting tree rings
Counting annual sediment layers deposited ice
and lakes.
Surface exposure dating
• scientists utilize more than one dating method in order
to maximize the accuracy and precision of their
findings
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PALEOCLIMATE STUDIES AND UNDERSTAND
POTENTIAL CONSEQUENCES OF FUTURE
CLIMATE CHANGE?• Every component of the Earth system is affected by climate.
Ecosystems
water availability
carbon cycling
sea level rise
ocean circulation
ocean acidification
All interact with the climate system and respond to changes in climate.
Paleoclimate studies provide an essential perspective for assessing the potential
impacts of future climate on natural systems.
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ARCHIVES• archives consist of geologic (e.g. sediment cores) and biologic (e.g., tree rings)
materials that preserve evidence of past changes in climate.
• climate proxies that can be sampled and analyzed using a variety of physical and
chemical methods
• Paleo climate records are preserved in marine, aquatic, and terrestrial settings from
around the world.
• Sediments
• Ice Cores
• Tree-Rings
• Speleothems
• Corals
• Packrat middens
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PRECAMBRIAN
• Precambrian period was the initial stage of earth history.
• It was the period of cooling of earth crust
• Demarcated by continues rain over many more years of time.
• Intense volcanic activity
• Outgassing
• Carbon dioxide rich environment
• Heat due to the presence of carbon dioxide and its birth it self.
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https://www.google.co.in/search?q=precambrian+climate&source
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CAMBRIAN PERIOD
• Cambrian, Ordovician, Silurian, Devonian, Carboniferous and
Permian periods.
• The sudden and repeated extinction events of trilobites
provides clues about the climate changes in the Cambrian.
• All of the continents were close to the equator and the
trilobites were adapted to warm waters.
• It has been suggested that the extinction of the trilobites was
associated with a cooling of the ocean waters.
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• This hypothesis is supported by the fact that it was only the deeper dwelling trilobites that survived the extinctions.
• cooling idea to explain the extinction is evidence that suggest that atmospheric CO2 was much higher in the early Paleozoic Era.
• This evidence is in the form of various mineral types whose presence is a sensitive indicator of atmospheric CO2 levels.
• Aragonite is a form of calcite, And very susceptible to dissolution if atmospheric CO2 is high..
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• Perhaps there were short periods of decreased pCO2 that
coincided with the cooling and extinctions
This diagram suggests that although that atmospheric CO2 was lower in the early part of the Cambrian it
may have been increasing by the end of the Cambrian
Source: https://earth.usc.edu/~stott/Catalina/Paleozoic.html
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Fig
Trilobite fossils
Source :
https://earth.usc.edu/~stott/Catalina/Paleozoic.html
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ORDOVICIAN PERIOD
• During the Ordovician Life expanded in diversity tremendously
• There were extensive reef complexes in the tropics.
• So the early Ordovician was thought to be quite warm.
• But the end of Ordovician Period there was a devastating mass extinction of organisms
• This extinction was one of the greatest mass extinction ever recorded in Earth History with over 100 families going extinct.
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• Suggesting two reasons. one is the continental drift and other
one is cooling of earth.
• The greatest extinctions occurred in the tropical oceans.
• If the oceans cooled because of the development of a large
ice sheet over the south polar region. the organisms adapted
to warmer tropical conditions would have few option to
migrate. This tends to support the idea that cooling lead to the
extinctions.
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Rich amount of reefs in Ordovician
source
https://earth.usc.edu/~stott/Catalina/Ordovician.html
North Africa is located over the pole in
the late Ordovician. Glacial deposits of
late Ordovician age were discovered in
Saharan Desert region. The picture
shows the depression in the rocks left
when a glacial boulder dropped on the
soft sediment and left a depression
which has been preserved for all these
millions of years.
Source
:https://earth.usc.edu/~stott/Catalina/Or
dovician.html
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SILURIAN PERIOD
• expansion of life following the mass extinction at the end of
the Ordovician.
• Silurian Period the first land plants appeared. Marine
organisms once again expanded in diversity following the
extinction of so many families in the late Ordovician.
• The Silurian was probably relatively warm even though pCO2
may have been lower
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Diversification of life during Silurian
Source
https://earth.usc.edu/~stott/Catalina/Ordovician.
html
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DEVONIAN PERIOD
• Devonian period is represented by the presence of large
amount of fishes.
• The first fossil evidence of insects and terrestrial trees comes
from Devonian age rocks.
• Devonian is thought to have been quite warm. Evidence of
this comes from the extensive amount of tropical-like reefs.
• The climate is also thought to have been quite dry. Evidence
of this comes from extensive evaporate (salt deposits) that
have been found dispersed much more broadly than any time
in the earlier Paleozoic.
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Today, for example, evaporates are
restricted to the mid latitude belt where
dry sinking air from the Hadley cells
make these regions dry. During the
Devonian these evaporate deposits were
found well beyond 30degree north and
south
sourcehttps://earth.usc.edu/~stott/Catalin
a/Ordovician.html
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• a mass extinction also reported from Devonian also.
• Mostly affected by tropical reefs
• This is mainly believed to happened due to the development
of glacial conditions once again over the south polar
regions and the cooling of the oceans which resulted from
this glaciations.
• The glacial deposits have been found in northern South
America which was located over the pole in the late Devonian
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CARBONIFEROUS PERIOD
expansion of life on land in
the carboniferous, including
early reptiles and in
particular, extensive land
plants in swamps.
Also note that the expansion
of these life forms occurred
following another major
extinction even in the middle
carboniferous.
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• Repeated glaciations and de-glaciations raised and lowered
sea level causing expansion declines of swamps throughout
the Carboniferous Period.
• The expansion of swampy wetlands with their rich plant life
extracted vast amounts of CO2 from the atmosphere.
• Amount of carbon that was extracted from the atmosphere to
form coal deposits in the Carboniferous Period.
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• There were very strong temperature contrasts between the
warm tropics and the cold polar regions.
• This would have produce vigorous atmospheric circulation.
• This is expected if the atmospheric circulation to the middle
latitudes was produce strong high pressure, dry conditions
where the Hadley cell descends around 30oN and South.
• The other important aspect to the development of evaporates
is the large land mass. The larger land mass would have been
much dryer on its interior since it was a long distance from the
ocean.
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diagram shows the effect sea level variations had on the
development of repeated cycles of coal and limestone sediments
during the Permian. During a transgression (sea level rise) the ocean
invades the land and floods the regions before covered by rivers,
streams and terrestrial sediments (coal). During a regression (Sea
level falling) the ocean recedes leaving the land exposed and rivers
flow once again over these exposed areas to form "Wetlands".
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Again cooling of the planet may be responsible for the devastating
extinction. We know that that the poles were cold and the perhaps this
era was the first time that glaciers formed over the north pole.
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MESOZOIC
• Mesozoic Era was very warm.
• No evidence of Glacial conditions
• Vertebrate fossils are found much farther north and south than
do reefs in the Mesozoic. But it is not clear if this is an
indication of seasonal migration or they were able to inhabit
colder northern climates.
• Tree Ring evidence from northern latitude sites seems to
support the idea of rather high seasonality (large temperature
contrasts between seasons).
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• Ferns have also been found at rather high latitudes from Mesozoic age rocks
• Ferns are an important clue to climate in the Mesozoic.
• Ferns that live today cannot tolerate freezing temperatures.
• In the Mesozoic Ferns are found at rather high latitudes
• But, Ferns in the Mesozoic may have been adapted differently to temperature than
modern Ferns.
• early and middle parts of the Mesozoic were quite dry over large portions of the
continents. We know this because of the extent of evaporite deposits.
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large peak in Evaporate deposits in the Triassic
and Jurassic Periods
Source
https://earth.usc.edu/~stott/Catalina/Mesozoic.html
Ferns imprinted on rock layers of Mesozoic
Source
https://earth.usc.edu/~stott/Catalina/Mesozoi
c.html
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CRETACEOUS
• One of the warmest periods in the Earth’s history was the
Cretaceous, from 140 to 65 million years ago.
• The Earth was then several degrees warmer than today and
is described as having a ‘greenhouse’ climate.
• The poles were warm and at times there may have been no
ice on them at all.
• There is even evidence of temperate forests growing in the
Arctic and Antarctic.
• As ‘greenhouse’ temperatures were reached, the world’s ice
melted, which caused significant sea level rise.
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Artist's impression of the Antarctic landscape during the Cretaceous
Source
http://www.bgs.ac.uk/discoveringGeology/climateChange/general/pastClimatesExamples.html
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TERTIARY
• Tertiary is divided in to palegene and neogene periods. And Paleogene again sub divided into Paleocene, Eocene and Oligocene epochs.
• The boundary between Eocene and Paleocene is marked by a period of Thermal maximum
• It was a rapid peak in the Earth’s temperature, a sudden global warming that resulted in the Paleocene-Eocene Thermal Maximum (PETM).
• It may be due to sudden release of greenhouse gases into the atmosphere.
• The sea temperature rose between 5–8 degrees celsius in just a few thousand years.
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• This sudden change in climate is associated with an extinction
event of marine species and changes in the circulation of both
the atmosphere and the oceans.
• The rapid rise in temperature, linked with an increase in
atmospheric greenhouse gases can be compared to our
climate today and for this reason it is of great interest to
researchers.
Fig no
Graph showing variation in polar ocean equivalent
temperature with respect to time in million years.
PETM shows high value
Source https://news.mongabay.com/2006/08/past-
climate-change-caused-dramatic-shift-in-humidity-
precipitation-levels-temperature-and-ocean-water-
salinity/
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QUATERNARY
• The Quaternary (the past 2.6 million years) has seen great
changes in the climate.
• Ice sheets to advance from the poles into usually temperate
places on the globe.
• Evidence shows that although there has been a progressive
long-term trend of global cooling during the Quaternary, there
have also been several different ice ages, or glaciations.
• Ice has advanced and retreated repeatedly, beginning at the
start of the Quaternary and continuing to the present day.
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• These repeated glacial episodes have resulted in significant
fluctuations in sea level and caused plants and animals to
migrate to more comfortable climates.
• Some that could not adapt or migrate became extinct.
• At the end of the Pleistocene (the earlier part of the
Quaternary, from 2 600 000 to 12 000 years ago) there was a
major extinction of large mammals, and animals like the
woolly mammoth became extinct worldwide.
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Fig no
Mammoth lived during quaternary ice age period
Fig no
mammoths are common in the fossil record. they are not fully fossilized but preserved as bones
Source : http://www.bgs.ac.uk/discoveringGeology/climateChange/general/pastClimatesExamples.html
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REFERENCE
• www.USGSpaleoclimateHome.com
• https://earth.usc.edu
• “Climate change through past”