CLIMATE CHANGE THROUGH GEOLOGICAL ERA DEEPCHAND V DEPARTMENT OF GEOLOGY UNIVERSITY OF KERALA TRIVANDRUM 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 in  sediments 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.. 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 • Perhaps there were short periods of decreased pCO2 that coincided with the cooling and extinctions 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. 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 Rich amount of reefs in Ordovician source https://earth.usc.edu/~stott/Catalina/Ordovician.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/pastclimate-change-caused-dramatic-shift-in-humidityprecipitation-levels-temperature-and-ocean-watersalinity/ 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”