CLIMATE CHANGE THROUGH GEOLOGICAL

ERA

DEEPCHAND VDEPARTMENT OF GEOLOGY

UNIVERSITY OF KERALATRIVANDRUM

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.

Fig 1

Geological time scale

Source :http://paleo.cortland.edu/tutorial/Timescale/timescale.htm

Fig 2 and 3

Geological time with evolution of life

Source: https://www.quora.com/Is-the-geologic-time-scale-useful

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.

PIONEERS OF PALEOCLIMATOLOGY

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.

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

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

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

Fig 5

Different archives and proxies used in climate change studies.

Source : www.USGSpaleoclimateHome.com

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.

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

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.

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

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.

https://www.google.co.in/search?q=precambrian+climate&source

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.

• 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..

• 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

Fig

Trilobite fossils

Source :

https://earth.usc.edu/~stott/Catalina/Paleozoic.html

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.

• 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.

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

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

Diversification of life during Silurian

Source

https://earth.usc.edu/~stott/Catalina/Ordovician.

html

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.

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

• 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

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.

• 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.

• 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.

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".

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.

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).

• 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.

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

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.

Artist's impression of the Antarctic landscape during the Cretaceous

Source

http://www.bgs.ac.uk/discoveringGeology/climateChange/general/pastClimatesExamples.html

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.

• 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/

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.

• 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.

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

REFERENCE

• www.USGSpaleoclimateHome.com

• https://earth.usc.edu

• “Climate change through past”