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Here is a compilation of term papers on the ‘Impacts of Climate Change’ for class 9, 10, 11 and 12. Find paragraphs, long and short term papers on the ‘Impacts of Climate Change’ especially written for school and college students.
Impacts of Climate Change
Term Paper Contents:
- Term Paper on the Impact of Climate Change on Igneous Process
- Term Paper on the Impact of Climate on Metamorphic Process
- Term Paper on the Impact of Climate on Weathering of Rocks
- Term Paper on the Impact of Climate Change on Formation of Soil, Sedimentary Rocks and Mineral Deposits
- Term Paper on the Impact of Climate on Desertification and Desert Landscape
- Term Paper on Climate Change and Mass Extinction
- Term Paper on the Ozone Depletion and Its Effects
- Term Paper on the Remarks on Impacts of Climate Change
Term Paper # 1. Impact of Climate Change on Igneous Process:
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Among the three groups of rocks (igneous, sedimentary and metamorphic), only igneous rocks could be formed by crystallization from the magma in the primitive Earth and when, the climatic condition became suitable (lowering of temperature, accumulation of water in the basins, precipitation) for weathering the sedimentary rocks were formed.
Metamorphic rocks were formed by transformation of both igneous and sedimentary rocks in the solid state at higher P-T conditions prevailing at depths of the crust (surface sedimentary and igneous rocks might have been sub ducted to depth by tectonic movement and were metamorphosed there).
The metamorphic rocks at depth and those igneous rocks which crystallized in magma chamber at various depths of crust are not subjected to change by climate, the domain of action of which is restricted to the surface or near-surface regions. However, such rocks when exposed to the surface either by erosion of overlying burden of rocks or tectonic movements, are affected by weathering process which is largely climate-controlled.
Magma, formed at deeper part of the earth’s crust (average depth ~35 km) or upper part of the underlying mantle, may crystallize at depth with gradual cooling over hundreds and thousands of years forming a coarse grained plutonic igneous rock (e.g. the rock gabbro crystallizes from a basaltic magma at depth, i.e. under plutonic condition). If the magma, instead of solidification at depth, finds its way upward through fractures in the crust, it will reach to the surface of the Earth either as volcanic eruptions or as fissure-fillings forming volcanic rocks.
Due to the sudden change of climate, i.e. exposure of the high temperature magma (1200°C) to the surface temperature (and pressure) of the earth it (now called lava) will rapidly crystallize, as a result of which a fine grained rock known as volcanic or extrusive rock will form instead of a coarse grained rock crystallized at depth. Thus a basaltic magma will crystallize a coarse grained rock (due to slow cooling), gabbro, at depth and a fine grained rock (due to rapid cooling), basalt, on the surface of the earth.
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If the basaltic magma extruded into the glacial region, it will consolidate so quickly that there will be very little or no time for crystallization of minerals (which have definite atomic arrangement) and hence the lava will solidify as dark coloured glassy rock, called tachylite. If the basaltic lava enters into the sea, it commonly crystallizes rapidly forming pillow-like structure forming pillow basalt.
The basaltic magma, before reaching the surface, may partly crystallize at depth slowly to minerals of coarse sizes; if such a partly crystallized magma, suddenly extrudes the surface, it will rapidly consolidate to fine grained basalt containing some earlier crystallized (at depth) phenocryst (coarse crystals of minerals) giving rise to porphyritic basalt. During solidification on the surface the gases trapped in the basaltic lava will exert pressure to come out forming vesicular structure on the exposed surface of the basalt.
Term Paper # 2. Impact of Climate on Metamorphic Process:
Metamorphism of crustal rocks takes place at depths at higher P-T conditions and hence metamorphosed rocks are not apparently affected by climate of the surface and near-subsurface domains until such rocks are exposed by erosion and tectonic activity. The excessive rainfall in a region may have some impact on metamorphic reactions taking place over a long period of time at crustal depth.
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The minute amount of water present in pore spaces of rocks has a profound effect in bringing about metamorphism. If the water concentration in the fluid phase of the rock at depth increases, a particular metamorphic reaction will take place at higher temperature in non-carbonate rocks than when the rock in question contains lower concentration of water.
However, in case of carbonate rocks (limestone undergoing metamorphism to marble) the higher concentration of water than CO2 in the fluid phase will cause the reaction CaCO3 (calcite) + SiO2 (quartz) → CaSiO3 (wollastonite) + CO2 to take place at lower temperature.
In the desert area the thunderstorm along a definite line on dune sand occasionally melts the quartz grains which solidify quickly (quenching) to silica glass, called Lechatelierite. Such silica glass occurs in a tubular form along a particular direction on sand dune, which may be attributed to the process of an ultra-metamorphism in which extremely high temperature of thunderstorm, a natural climatic phenomenon, has completely melted the crystalline quartz followed by quenching within a few seconds.
Term Paper # 3. Impact of Climate on Weathering of Rocks:
Mechanism of Weathering:
Weathering is a climate-controlled process by which rocks and its constituent mineral grains, the most important constituent of geologic system, are broken into smaller and smaller pieces and the constituent mineral grains are separated from one another and some minerals are decomposed to other minerals.
Some of these loose materials may remain practically in the same location on the partially altered bed rock while the others are transported by gravity, wind and surface run-off, the later also includes dissolved ions-to lakes, streams, rivers and ultimately ocean for deposition and/or precipitation as sediments forming eventually sedimentary rocks.
There are two processes of weathering, physical and chemical. In physical weathering solid rocks are fragmented by physical processes. For example, the exposed rocks in the day time, when the temperature is higher, undergo expansion and in the night, when temperature is much lower, undergo contraction; continuity of this expansion and contraction for several years, eventually break down the rocks and mineral grains into smaller pieces.
The other processes of physical weathering include:
(i) The separation of sheets of homogeneous and un-layered rocks, such as granite, due to release of load pressure on the underlying un-weathered rock by the removal of the overlying weathered materials,
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(ii) Frost wedging in which water, percolated into fractures of rocks, freezes to ice whose greater volume (9 per cent greater than that of liquid water) exerts a force great enough to split rocks,
(iii) Salt wedging in arid climate of desert where salt (NaCl), due to evaporation of water below the rock surface, exerts pressure giving rise to flaking of rock,
(iv) Biological disintegration of rocks or rock particles by growth pressure of tree roots in weak zones of rocks and activity of worms and
(v) Disintegration of fragmented materials by saltation and abrasion in river beds or beneath glaciers.
Chemical weathering, in contrast, causes chemical alteration of minerals present in rocks, which further helps disintegration. In reality, both physical and chemical weathering’s occur together and both contribute to mass movement. High temperature and heavy rainfall accelerate chemical weathering, cold and arid (for example, desert) climates impede the process.
Chemical weathering is most active in warm, humid areas where rainfall supports plant growth that yields humid and organic acids to facilitate chemical reactions. The agents for decomposition at the surface are water, oxygen, carbon dioxide, heat, acids, alkalies, plants and animal life and some of the soluble materials produced by decomposition of the rocks themselves.
The chemical reaction between minerals in rocks and air and water, facilitated by higher temperature, results in chemical weathering.
The SO2, NO2 and CO2 in the atmosphere react with H2O (occasionally O2) to form different acids as follows:
The acidic water thus formed attacks rocks, particularly limestone or marble:
Some of the reactions, grossly oversimplified, that take place by chemical weathering of rock minerals are:
Carbonic acid (H2CO3), formed by the reaction of CO2 with rain water in the atmosphere, is a powerful reactant in the weathering of carbonate and silicate rocks. In addition to the atmospheric contribution of H2CO3 in rain water, the organic matter in the soil at the surface can increase the acidity of reacting waters through the introduction of organic acids. The immense chemical weathering in tropical and subtropical humid climates is facilitated by high precipitation and temperature coupled with high organic acid concentration.
The rounded form of the granitic rocks and dolerites is the result of both physical and chemical weathering. Both the rocks are rather impermeable and hence, acidic water percolates through the fractures ultimately bringing about what is known as spheroidal weathering. The gypsum formed on marble by reaction, as shown above, is easily washed away by rainwater, thus altering the polished marble to a rough surface.
Term Paper # 4. Impact of Climate Change on Formation of Soil, Sedimentary Rocks and Mineral Deposits:
Soil:
Soil, more particularly fertile soil, is one of the most important precious natural resources and is a medium for growing food, timber and wood. A hand specimen of soil contains billions of microbes that decompose plant, animal and mineral matter and generate nutrients. Soils are the result of interaction among the lithosphere, atmosphere, hydrosphere and biosphere. The broad principles of rock weathering which give rise also to soil.
The soil is defined as an internally organized, natural body of weathered minerals and organic constituents. The soil sphere or pedosphere varies in thickness from lm to 200m. The depth of the pedosphere is greater where rainfall and temperature are high and weathering process extends deeply in the crust. The soils are arranged in horizons such as O horizon (top), A, B, C, R etc. horizons, the vertical sequence of which is called soil profile. The characteristics of soil horizons vary with climate (moist, dry, and wet). Clays are important constituents of soils.
Clays are formed by chemical weathering of feldspars and some other silicate minerals of rocks. The dying plants and animals contribute organic matter, the decay of which releases CO2 and nutrients. Most of this CO2 recirculates to the atmosphere (thus adding to the greenhouse gas of the atmosphere). The weathering of rocks releases sodium, potassium, magnesium, calcium, chloride and other ions to the soil.
The nature of the soil is controlled not only by the composition of the bed rock but also by the climate-dependent weathering process. The nitrogen from atmosphere enters the soil and back through a series of biological transformations.
Sedimentary Rocks:
The basic requirements for formation of sedimentary rocks are the availability of loose sediments by weathering of preexisting rocks, transport by gravity, wind and water to the basin of deposition such as lakes, rivers and ultimately sea forming clastic sedimentary rocks within the broad range of surface pressure-temperature conditions. The root cause is weathering, both physical and chemical, which is dependent on climate – the higher temperature accelerating the process.
The precipitation of some sediments from aqueous solution in lakes, rivers and abundantly in sea water is controlled by some factors such as pressure, temperature, Ph and Eh (oxidation-reduction potential) and concentration; such rocks are called chemical sediments or non-clastic sediments (e.g., chert and most limestones of the sea bed). Some examples of impact of paleo-climate on sedimentation are briefly described below.
The discovery of detrital or clastic mineral zircon (age: 4400-4200 m.y. old) in meta-sedimentary complex of Australia, indicates that weathering of primary igneous rocks forming the primitive crust commenced probably around this time interval or slightly younger and ocean basin, presumably having shallow water depth, was formed in the early period of the earth. The record of increasing amount of sedimentary rocks from 3900 Ma to 2500 Ma (Figure 3.1) indicates that climatic conditions for weathering and sedimentation were favourable.
However, lower free oxygen concentration in the then atmosphere and hydrosphere did not allow formation of much Red beds (red colour is due to oxidation of iron) and evaporates like gypsum and anhydrite rocks and oxidation of pyrite (FeS2). The common presence of warm humid climate with a general drying out of global climate caused increasing formation of arkosic sedimentary rocks until about 2000 m.y. (Figure 3.1).
The increase of free oxygen in the atmosphere between 2500 and 2000 m.y. and/or luxuriant development of algae in the vast ocean supplied oxygen for the oxidation of dissolved ferrous iron so as to precipitate Fe2O3 (hematite) giving rise to banded iron formation (BIF) mostly during Archean-Proterozoic boundary, 2500-2200 Ma. The warm humid climate from 2500-570 Ma (Proterozoic) and more oxidizing condition caused abundance of Red beds and arkoses and also precipitation of warm-water carbonate rocks, limestone and dolomite.
The substantially warm climate of Cambrian to Devonian, similar to present day or slightly higher temperature favoured sedimentation of evaporites in Cambrian- Ordovician time in Australia, Siberia, the Aden-India, the Spanish Sahara, Canada and USA and of halites (NaCl) in Eurasia, and anhydrite (CaSO4) in Americas. In Silurian evaporites occur in latitude < 25° while Devonian evaporites in Asia extend to 60°. The high humidity and warm climate in Devonian, restricted to relatively lower latitudes, caused formation of coals (amphibians appeared at this time).
In early Carboniferous the same climate favoured growth of organic reefs in low paleo-magnetic latitudes (e.g., ‘Horseshoe Atoll’ of the Midland Basin, Texas). In the Upper Carboniferous to Lower Permian glaciations in the southern hemisphere caused formation of glacial boulder bed or till at the base of Permian strata of the Gondwanaland. With increasing warming and humidity from the basal beds of Permian to the upper part the development of luxuriant Glossopteris flora gave rise to rich coal deposits of the Lower Gondwana rocks.
Gossopteris became almost extinct in the Triassic when the climate changed to arid condition giving rise to the appearance of Dicroidium flora, which, in turn, was replaced by Ptilophyllum flora in the Jurassic Gondwana due to the reappearance of warm humid climate. The warm tropical climate may have favoured the development of robust ectotherm labyrinthodont amphibians and reptiles in the continental Permian rocks in different parts of the Earth.
The fossil vertebrates (for example, Lystrosaurus in South Africa, Europe, Gondwana rocks of India, Asia, North America, recorded from Triassic and Jurassic rocks indicate moist, tropical to subtropical conditions. The Lower Triassic oxidizing arid climate favoured deposition of Red beds (between 50° latitudes, encompassing much of Europe, former USSR, North America and Northern Brazil).
The distribution of hermatypic hexacorals, Dictyophyllum and Sagenopteris, the land-living giant reptiles (as far north as 50°N), marine reptiles, Plesiosaurus, and marine crocodiles indicate warm climate. The Late Jurassic is known as the age of giant dinosaurs in the reptilian faunas of the world. Oxygen isotope data from Jurassic belemnites at 75°S latitude just off Antarctica indicate that sea temperature reached 14°C (roughly 7°C higher than average temperature today) as suggested by Merritts et al (1998).
The warm oxidizing climate of Jurassic favoured formation of evaporite sediments. The Cretaceous climate was warmer than now which is indicated, among other evidence, by abundance of oxygen isotope paleo-thermometric data over the full range of latitudes from equator to poles (Figure 3.2), which promoted formation of evaporites, coals, reefs and bauxites.
The Cretaceous climate corresponds to tropical to subtropical conditions and beyond 70°S latitude the climate was warm to cool- temperate. The striking feature of Cretaceous is the enormous accumulation of heat within the atmosphere-ocean system.
Sedimentary Mineral Deposits:
The warm climatic condition facilitates the evaporation of lake water or sea water to give rise to direct precipitation of salts yielding evaporite deposits such as sodium carbonate, sodium sulphate and borax. Marine evaporites form when a portion of the shallow sea becomes cut off from the main part of the ocean by a reef or other barriers. The most important salts that precipitate from sea water are gypsum (CaSO4, 2H2O), halite or common salt (NaCl).
The sedimentary mineral deposits formed by precipitation from sea water solution are phosphates, iron deposits (e.g. banded iron formation) and manganese nodules. It may be mentioned in this context that average content of iron in river water is about 1.0 ppm whereas in seawater the amount is exceedingly small, about 0.008 ppm. Thus weakly acidic iron-bearing solution flowing into the sea from neighbouring land areas must precipitate most of their iron in the weakly alkaline marine water.
The concentration of heavy minerals takes place by mechanical process (for example, winnowing action of waves and currents of the river or sea water).The deposition of such heavy mineral concentrates in suitable places of the river or sea water gives rise to placer deposits (example: placer gold, platinum, diamond, monazite etc.).
Residual Mineral Deposits:
Due to weathering of rocks soluble parts may be removed and the insoluble parts may be concentrated over the bed rock to form residual mineral deposits. In temperate climate, silica of silicate rocks is not extensively removed but forms clays with other constituents. Thus residual clays or clayey soils are common products in all temperate climates.
Tropical and subtropical climates, characterized by alternate wet and dry seasons, warm weather and warm surface waters throughout the year and generally luxuriant vegetation with profuse supply of bacteria and organic compounds promote rock decay, more leaching, more thorough decomposition of silicate rocks and removal of silica in solution.
The wet season of the tropics allows formation of Al2O3 and Fe2O3 and dry season allows removal of SiO2 in solution. Thus, instead of clay (hydrous aluminium silicate), hydrous aluminium oxide (bauxite) is formed as a residual mineral deposit in the tropical-subtropical climates.
The conditions necessary for formation of bauxite as a residual deposit are:
(i) A favourable parent rock (high in aluminium silicate minerals and low in iron and free quartz or absence of quartz, e.g. nepheline syenite) with easily soluble minerals whose leaching will leave a residual enrichment of aluminium and/or iron (for laterite deposit),
(ii) Humid tropical or subtropical climate,
(iii) Effective rock porosity permitting free circulation of water,
(iv) High rainfall with intermittent dry spells,
(v) Good drainage,
(vi) Low to moderate topographic relief,
(vii) Availability of reagents to bring about breakdown of the silicates and solution of silica,
(viii) Presence of vegetation including bacteria, (be) prolonged stability, and
(x) Preservation.
In the temperate regions of Arkansas, Georgia and France the large bauxite deposits were formed during warmer Tertiary climates. Most of the commercial deposits of bauxite in the world are found between Middle Cretaceous and Middle Eocene indicating that optimum conditions for their formation, say temperature, existed during this time (Figure 3.2). However, some Paleozoic and Late Tertiary to Recent bauxites are also known Apart from bauxite, valuable deposits of iron ore, manganese, clays, nickel, phosphate, kyanite, barite, ochers, tin, gold and few others are known as residual deposits.
Supergene Mineral Deposits:
Climate plays an important role in enriching the ore content of an ore body. The key process in this enrichment is weathering. The warm humid climate of the tropical areas accelerates the process. Weathering may expose a low grade ore body of depth to the surface of the earth by removal of overlying economically unimportant weathered rock material.
During further weathering, the surface water, while percolating through the low grade ore body, reacts to yield solvents which dissolve valuable materials. Thus many of the valuable materials are leached out from the upper oxidized zone and trickle downward to the water table.
The zone above the water table is called the oxidized zone. In this zone of oxidation the leaching solutions may lose a part or all of their metallic content and give rise to oxidized ore deposit which may be viable for commercial exploitation. However, when the down trickling solutions penetrate the water table, below which is the zone of reducing environment, the metallic content maybe precipitated in the form of secondary sulfides giving rise to a zone of secondary or supergene sulphide enrichment of the sulphide protore (the primary unaltered ore body).
Below the zone of supergene enrichment of ore body lies the lower grade unaltered protore. Copper, zinc and silver sulphides are soluble in the upper part of the ore body in the oxidized zone and are more susceptible to supergene enrichment. Apart from climate, the other factors which accelerate supergene enrichment are water table, rate of erosion, time, chemical, structural and textural properties of the enclosing rocks and physiographic development of the area.
Oxidation of the protore at the surface/near-surface zone is the primary requirement for supergene enrichment. Supergene ore bodies occur in many of the non-glaciated land areas of the world.
Term Paper # 5. Impact of Climate on Desertification and Desert Landscape:
The areas of little rainfall are eventually converted into deserts. They are primarily located between 15° and 30°N and S of the equator. This zone is dry due to global circulation pattern of atmosphere. The deserts of Africa, Australia and North America lie within this zone.
However, some of the semiarid lands and deserts (North America and Central Asia) are dry lands because they are situated far in land in continents or in the “rain shadow” of mountain ranges that create obstruction to the rainfall and storms and some deserts (Chile and Peru) are due to intercept of air by a cold offshore ocean current.
Human-induced land degradation, in addition to natural disastrous drought, together caused deaths of 250,000 people and several million cattle, sheep, goats and camels in the Sahel region of West Africa in the early 1970s.
The impacts of desertification are:
(i) Lowering of groundwater table,
(ii) Salinization of soil and near-surface soil water and
(iii) Reduction in aerial extent of surface water in streams, ponds and lakes.
In the desert area, the physical weathering is predominant partly due to scanty rainfall and mainly due to scorching heat at day time and severe cold at night, eventually disintegrating the rocks due to expansion and contraction during several years. The high wind velocity in the desert area causes enormous amount of dusts to darken the sky and these dusts are carried over great distances.
These wind-blown sands not only abrade each other but also the rock surfaces. As a result the sand grains become finer and gradually rounded due to innumerable impacts. The sand grains (1-2 mm in diameter) become well-rounded like ‘millet-seed’ while the finer grains (0.006-0.2 mm in diameter) become generally angular. Due to winnowing action of the wind the transported particles become sorted.
Thus the wind-blown dune sands are relatively clean and composed of uniform grains commonly with frosted surface. Ripple mark, formed by gentle wind, is a common feature of dune sands. The finer particles are blown out and the larger fragments, such as pebbles and gravels are left behind and concentrated on the wind-swept surfaces of the original rock waste.
The term dime is used for wind-blown sand deposits which frequently form mounds or ridges.
The dunes show three geomorphological types:
(i) Transverse dimes,
(ii) Crescent-shaped dunes, called barchans (Figure 3.3) and
(iii) Longitudinal dunes (sand deposited in rows of long linear dunes the axes of which are more or less equally spaced and parallel to regional wind direction).
In barchan the crescent wings point downward and the curving bow faces the wind. If the wind directions vary, the barchan dunes are unstable and instead the dunes are strung out in long chains at an angle to the winds and such dunes are called seif (meaning in Arabic, ‘sword’). The height of some seifs in Iran is more than 700 feet above the base and 3/4ths of a mile wide. The length of individual seif ridges may be as much as 60 miles and the length of groups of seifs extend more than 200 miles in western Egypt.
Apart from the above geomorphological types of sand dunes the wind erosion produces three other types of landscape in the desert surface such as:
(i) The rocky desert the hammada or hamada of the Sahara,
(ii) The stony desert composed mainly of gravels or pebbles (the reg of the Algerian Sahara, the serir of Libya and Egypt or the gibber plain of Australia) and
(iii) The sandy desert (the erg of the Sahara).
In the desert area the sand blasts erode away the inclined softer bed rocks which may alternate with harder bed rocks, thus forming ridge-and-furrow structure or passages between deeply undercut ridges, which are called yardangs in Asiatic deserts. The wind-blown sand may form also smoothed or pitted structure on the exposed bed rock of the desert floor. For example, massive granitoids become smoothed or pitted, gneisses develop rib and flute structures, particularly when the gneissic foliation plane is parallel to the wind flow direction, whereas compact limestone becomes polished by wind-blown sand.
If there is seasonal change of wind direction or the pebbles in the desert are turned over by wind flow, two or more facets may be cut by wind blast and each pair of facets meet in a sharp edge. Such wind-faceted polished pebbles are called ventifacts or dreikanter.
Term Paper # 6. Climate Change and Mass Extinction:
The signature of oldest life, till now claimed to have been recorded (a yeast-like spherical microorganism Isuasphaera, a dubiofossil) is from a metamorphic rock ~3800 m.y. old from Isua Geenstone Belt, Greenland. Since then both evolution and extinction and occasionally mass extinction of mainly animals throughout geologic history of the earth have taken place and have been recorded from the rock formations of different ages. By mass extinction we mean significantly higher rate (than normal) of death of life within a short time frame and over wide geographical areas.
The major Mass Extinction events have been recorded from the rocks of the following geological times:
(1) Late Precambrian;
(2) Early Precambrian;
(3) Late Cambrian;
(4) End Ordovician (death between 70 and 80 per cent of all species and 22 and 33 per cent of all families);
(5) Late Devonian (between 70 and 80 per cent of all species and 20 per cent of all families);
(6) End Permian (between 70 and 95 per cent of all species and between 50 and 60 per cent of all families);
(7) End Triassic (80 per cent species and 20 per cent families);
(8) Late Cretaceous;
(9) End Cretaceous (between 46 and 76 per cent of all species and 14 per cent families);
(10) End Paleocene;
(11) End Eocene;
(12) Pleistocene;
(13) Holocene [since 17th century 116 species of birds (1 per cent of total number), have been extinct and 1029 species (11 per cent) are threatened or endangered].
Causes of Mass Extinction: Role of Climate Change:
The causes of mass extinction can be classified into two groups:
(1) Intrinsic, (earth-bound causes) and
(2) Extrinsic (extraterrestrial causes).
The intrinsic causes include volcanism, sea-level change and associated anoxia and climate. The extrinsic causes include bolide impacts and associated effects. Whatever the causes might be, the ultimate effect is climate/environment change leading to mass death of life during a span of short time interval repeatedly in the geological history of the earth. It is interesting to note that there are differences in the levels of extinction between the animal and plant kingdom. This is partly due to the greater ability of plants to withstand major ecological trauma.
1. Intrinsic Causes:
A good correlation between flood basalt magmatism and mass extinction events during the Palaeozoic to Upper Cretaceous has been shown by Rampino and Stothers (1988). Flood basalt volcanism would emit huge amount of dusts and several gases including greenhouse gases and other toxic materials causing darkening of the sky which obstructs solar radiation causing ‘volcanic winter’, stop of photosynthesis, intoxication of the atmosphere, global warming due to accumulation of CO2 and other greenhouse gases and ultimately acid rain; wildfires may also be generated affecting the atmospheric composition.
Intermittent basaltic volcanism simultaneously in different places of the Earth during over a few million years, for example, Palaeozoic to Upper Cretaceous basaltic volcanism as demonstrated by Rampino (1987), might cause climatic changes bringing about mass extinction. In India, wide-scale flood basalt volcanism of Deccan Traps in a major part of Central and Western regions took place about 65 m.y. ago (Upper Cretaceous), thus coinciding with the Cretaceous Tertiary (K/T) mass extinction event.
Ocean Anoixic Events (OAE) are suggested by some to be correlatable with many mass extinction events. The oxygen- poor condition may develop at a depth of the ocean due to high rate of organic carbon deposition in the sediments there and during such change mass extinction of biota might have taken place. The geological evidence of such OAE have been recorded from Palaeozoic and Mesozoic marine sediments from different parts of the world.
A number of factors may cause OAEs, such as dissociation of methane from deep sea hydrates causing increase of greenhouse gases CO2 and CH4, changes in ocean circulation patterns and water temperatures, periods of marine transgressions, increase in nutrient supply and productivity, changes in salinity of bottom water and influx of organic matter.
The OAEs have also been connected by some authors to global tectonic pulsations such as rapid sea-floor spreading and increased volcanism giving rise to increase of atmospheric CO2 and warm climate and warm stagnant bottom waters. Ocean turn-over events giving rise to mixing of anoxic water throughout the ocean-water column may have been caused also by bolide impacts. A model of OAE development by increased influx of trace metals (e.g. Fe, Co, Mn, Mg, Mo, Sc) has been suggested.
According to this model, the increased trace elements would bring about high phytoplankton productivity and eventual death and extinction when the toxic levels had reached the levels of upper limit of tolerance by the marine animals. The different sources of the trace metals detected at bio event boundaries are extraterrestrial, volcanism, global wildfires, acid rain and upwelling of anoxic deeper water. The correlation among mass extinctions, large-body impacts, OAEs and flood-basalt volcanism led Leary and Rampino (1990) to propose multiple-related causes for mass extinctions.
2. Extrinsic Causes:
Bolide impacts include impact of meteorite and also showers of comet. The theory of multiple large-sized meteorite impacts causing physical and chemical stresses imposed on biota leading to stepwise extinctions over a period of few million years has received much attention and momentum after the discovery of Chicxulub meterorite impact crater (diameter 180 km) in the northern Yucatan Peninsula, New Mexico, about 65 m.y. ago (K/T boundary).
“Discovery of anomalous iridium and other trace metals in generally chondritic (chondrite, the most abundant type of meteorite) ratios in a thin band of clay, coinciding with the major mass extinction of nannoplankton and foraminifera at more than 75 sites worldwide and subsequent discovery of microspherules, shocked quartz and feldspar grains and soot in the boundary clay layer provided evidence for the impact scenario”.
The source of iridium in the clay bed at the basal part of Tertiary sedimentary rocks is thought to be the meteorite, the impact of which in Upper Cretaceous time (65 m.y). Created pulverization of the impacted rock and this pulverized masses were transported for deposition in the water basin to form iridium-rich clay bed in the younger Tertiary time (K/T boundary). According to some authors the iridium anomaly may also originate by repeated volcanism. The atmospheric changes caused by prolonged volcanism may be created also by meteorite impacts.
The specific causes of some of the important mass extinction events suggested by different authors are summarized in Table 3.1.
Impact of Glacial Climate:
The earth has witnessed glacial climates in varying extent repeatedly throughout its history. The earliest large glaciations took place in Middle Precambrian and mostly around 2300 m.y. ago in several continents. The second large glaciations between the range of 900 to 600 m.y. ago (Precambrian) occurred in continents which were then located at low latitudes. In Palaeozoic time, glaciations have been recorded during four periods.
Of these, the Middle Carboniferous to Early Permian glaciation was the most intense and of great duration. Among all the glaciations, the Late Precambrian, Late Paleozoic and Late Cenozoic glaciations were probably the most extreme, judging from the areas affected. During the Pleistocene epoch (~1.8 m.y. ago) glaciers occupied as much as 30 per cent of the land area of the earth. This is referred to as Ice Age. Around A.D. 1400 the cold period is known as Little Ice Age. Today glacial ice occupies 10 per cent of the land area.
Three causes have been suggested for the development of glacial climate:
(1) The amount of solar radiation reaching earth’s surface has regularly changed cyclically (called Milankovitch cycles) and results from regular changes in earth’s orbit and orientation of earth’s axis of rotation,
(2) Decline of CO2 in the atmosphere (CO2 in glacial time, ~190 ppm and during interglacial time, ~280 ppm, as recorded from the ice core samples of Antarctica) and
(3) Changes in the circulation patterns of the oceans and atmosphere. If there was no greenhouse effect, the earth would be approximately 33°C cooler than it is now and all surface water would be frozen.
Some of the impacts of glacial climate on the geologic system are summarized below:
1. The landform is variously changed by glacier movement. For example, it may convert V-shaped valley in the hilly region, which is characteristic for river erosion, into U-shaped valley in the landscape.
2. Glacier movement erodes the basement and lateral wall rocks which may be deposited on pre-glacial river valleys forming till deposits (highly unsorted sediments whose sizes vary enormously from boulders to very much fine clays). A glacier boulder bed, known as Talchir boulder bed, occurs at the base (Upper Carboniferous or Lower Permian) of the coal- bearing Gondwana rocks of Peninsular India.
The characteristic feature of the fine grained sandstones deposited in river basin during this glacial climate is the presence of unaltered feldspars which undergoes alteration with increasing temperature and moist climate in the overlying coal-bearing Barakar sandstones in the basal Gondwana rocks of India. Varve sediments (composed of thicker layers of coarse materials alternating with thinner layers of fine grains) are deposited in fluvioglacial lakes by alternate summer and winter climates.
3. The plant fossils (Glossopteris flora) recorded from the basal part of the Gondwana rocks, which experienced glacial climatic condition, are narrow in contrast to the much coarser luxuriant flora present in the overlying Barakar and Ranigunge rock formations in India.
4. Ice avalanche in Pune, “triggered by a great earthquake in 1970 killed about 20,000 people while burying several villages in debris”. When glaciers enter into sea (icebergs), the movement of the icebergs into shipping lanes may cause hazard to navigation (for example, Titanic disaster of April 15, 1912 and claiming 1501 lives). The mixing of volcanic eruptions on a mountain peak with the glacial ice on the slope may result in volcanic mudflows which may destroy property and human lives.
5. Glaciation gives rise to two main types of glacial landscapes:
(i) Dome shaped glaciers which submerge the topography and
(ii) Glaciers which flow in channels.
The other types of landscapes formed by glaciers, which submerge the topography, occur as:
(a) Ice-sheets of continental size, for example, Antarctic and Greenland Ice-sheets with volume of 27 x 106 km3 and 2.6 x 106 km3 respectively,
(b) Ice-caps, which are smaller ice-domes, for example, Vatnajokoll in Iceland and Penny and Barnes ice-caps in Baffin island and
(c) Summit Ice-caps, which are small glacier domes covering some flat-topped mountains, for example, Kibo summit of Kilimanjaro in Tanzania.
The glaciers which flow in channels include:
(a) Valley glaciers, which are long compared with their width and
(b) Cirque glaciers which are relatively small ice bodies occupying cirque hollows high on mountain sides, the width and length of the glaciers having similar magnitude.
6. Glacial climate cause perennially frozen ground called permafrost. In polar and high mountain regions permafrost is present where average annual temperature is less than -2°C. The permafrost depth maybe several hundred meters. In the summer the surface of permafrost undergoes melting to a water-saturated layer up to 1 to 2 m thick. During strong winter cooling and contraction, polygonal cracks are developed in permafrost, which is called tundra polygons.
Such polygons may be several hundred meters in diameter. The continuous permafrost areas are Greenland and northernmost Asia and North America. The discontinuous permafrost occurs towards south of the above regions and percentage of unfrozen ground increases towards lower latitudes. About 99 per cent area of Alaska is covered by continuous and discontinuous permafrost; its thickness varies from 400 m in the north to 0.3 m at the southern margin of the frozen ground.
7. Glacial climate causes change in the shell chemistry of some organisms. For example, the oxygen isotopic composition of the CaCO3 shell of foraminifers from the ocean of glacial climate is enriched in 18O than 16O in comparison with the ocean water whereas in the foraminifers from the warm interglacial ocean this ratio (18O/16O) is lower. This temperature dependence of oxygen isotope composition of calcite (CaCO3) precipitating in the sea water was discovered by H. Urey and has been a powerful tool for palaeo-temperature determination.
In drill core samples of Neogloboquadrina pachyderma from Norwegian Sea, it has been observed that one species of this foraminifer shows right coiling in ice-free surface waters and another species shows left coiling where sea ice is common.
8. The lava erupted through sub-glacial volcanic vent will melt the overlying glacial ice. As a result, due to very rapid cooling of the lava, glassy or extremely fine-grained solidified rock and hyaloclasites will be formed. If the lava is of basaltic composition, basaltic glass, pillow basalt and pillow breccias will be formed by chilling.
The typical shape of the sub-glacial volcano is flat-topped, steep-sided and this type is called tuya (named after Tuya Butte in British Columbia). Such sub-glacial volcanoes can cause dangerous floods due to melting of ice and ‘lahars’ or mud flows formed by mixing of the ice-melt with ashes given off by the volcano. Such volcanoes most commonly form today in Iceland and Antarctica.
Impact of Pleistocene Climate:
Pleistocene and Holocene (or Recent) epochs are the final two epochs of the Cenozoic Era (Figure 3.2) and represent about 2 m.y. or so; the widely accepted age of beginning of Pleistocene is 1.8 m.y. During Pleistocene, over 40 million km3 of snow and ice accumulated on about one-third of the land surface of the globe. The Pleistocene ice age is suggested by some geologists to have ended between 11000 and 12000 years ago.
However, historical records and C-14 dating of old terminal moraines suggest that cold rushes have recurred periodically into the Holocene. The period between AD 1500 and 1900, witnessed cooler and drier conditions (temperatures were often 2° to 4° F cooler than today) and this spell of interval is called the Little Ice Age.
The impacts of Pleistocene glaciations are summarized below:
1. In the northern hemisphere the climate zones were expanded southward and the USA and northern Europe (high latitude) developed Arctic conditions. On the other hand rainfall increased in lower latitudes causing generally beneficial effects on plant and animal life. The presently arid regions in north and east Africa, even as late as the beginning of the Holocene, were well-watered, fertile and populated by nomadic tribes.
2. It is estimated that the sea level may have fallen at least 75m during maximum ice coverage. A land bridge stretched from Alaska to Siberia and the British Isles was joined to Europe.
3. Glacial landforms developed extensively and the great weight of the ice depressed the crust in large parts of the glaciated area to a level of about 200 to 500m below the pre-glacial position; and with the removal of the glacial ice sheet, down warped areas began to return to their former positions.
4. The old drainage channels were changed and new channels were created by the movement of the great continental glaciers.
5. The great lakes of North America are shown to have been formed by movement of glaciers to low land to scour them deeper and subsequent melting.
6. Glacier movement transported fertile topsoil from over the bedrock in many areas forming productive farm lands away from the original location of the topsoil.
Term Paper # 7. Ozone Depletion and Its Effects:
Although ozone (O3) is a minor constituent of the atmosphere (mainly present in the stratosphere and maximum concentration occurs around 25 km altitude) the discovery of ozone hole (a circular area in the atmosphere remarkably depleted in ozone) at Antarctica in 1985 by Farm an and his associates, has been a great concern over the world because ozonosphere acts as a shield against the harmful UV-radiation coming to the earth’s surface.
Figure 3.7 shows the dramatic ozone depletion in Antarctica. Among the three types of UV-radiation (UV – A, UV – B and UV – C), UV – C (wavelength range 2000 – 2800 Å) and UV-B (wavelength 2800 – 3200 Å) are lethal to man and many living organisms and are totally absorbed by ozone layer whereas UV – A radiations (> 3200 Å) is relatively harmless and is absorbed only slightly by atmospheric ozone.
Midya and Jana (2002) have reviewed the atmospheric ozone depletion and its effects on environment. Ozone is depleted by UV- radiations, volcanic eruptions, HOx, CI – Br, CO and HOx, NOx, polar stratospheric clouds and greenhouse gases such as CO2, CH4, N2O, Chloroflurocarbon – 11 (CFCl3) and Chloroflurocarbon -12.
Direct exposure to UV-radiations causes acute sunburn, skin pigmentation and neomelanogenesis skin cancer, squamous cell carcinoma and basal cell carcinoma. The least frequent but more aggressive is cutaneous malignant melanoma. Squamous cell carcinoma has been reported in cattle, horses, cats, sheep, goats and dogs. The eye is the principal route of exposure to UV-radiation and its cornea is affected first, followed by the lens, the vitreous humor and the retina.
The other ocular effects include photokeratitis, climate droplet keratopathy, pinguecule, pterygium and squamous cell carcinoma of the cornea and conjunctiva. Midya and Jana (2002) predicted in the 1992 Copenhagen Amendments that the calculated number of skin cancer caused by the ozone depletion will exceed 33,000 per year in the USA and 14,000 per year in northwest Europe around the year 2050.
The ozone depletion is observed everywhere which threatens the human species and other animals as well as plants (e.g., bacterioplankton, picoplankton, cyanobacteria, phytoplankton and zooplankton). The function of cyanobacteria, which reduces atmospheric nitrogen into ammonium ions for aquatic eukaryotic phytoplankton, is hindered by UV-B radiation.
The UV- radiation affects also the photosynthetic functioning of phytoplanktons, the biomass producer in aquatic ecosystem living at the top layer of the oceans and fresh water (euphotic zone). UV-radiation changes also the tropospheric chemistry causing increase of HOx, CH4, CO and H2O2.
No record of life older than 3900 m.y. has yet being discovered. It means that possibly life did not appear before this time. One of the possible causes may be that the protective ozone layer was not formed and hence the harmful UV-radiations could hit the earth surface directly before 3900 m.y.
The majority of research on early life comes from 3 localities:
(i) The Isua Group rocks (3900 – 3700 m.y. old) in southwest Greenland including the island of Akilia;
(ii) Barberton Greenstone Belt rocks (3550 – 3330 my. old), Kaapvaal craton of South Africa;
(iii) Warrawoona Group of rocks (3515 – 3427 m.y. old).
The earliest life probably consisted of anaerobic chemosynthetic micro-organisms which are believed to have lived in a reducing environment and hence free oxygen was not present in appreciable amount, not to speak of ozone. Alternatively, it has also been suggested that early life appeared a few centimeter below the surface of water where the UV-radiations could not penetrate. With youngling of the geological time more and more free oxygen was formed in the atmosphere and when the protective ozone layer developed in the atmosphere life appeared in increasing amount.
Today, with increasing accumulation of greenhouse gases, particularly CFCs in the atmosphere the stratospheric ozone shield is being destroyed which has become a threat to man, a component of the geologic system.
The Montreal Protocol of 1989, in which are now included 140 countries or so, decided to phase out CFC products by 1996 and set up a fund paid for by developed nations to help developing nations switch to ozone-safe chemicals. The Montreal Protocol is a model for cooperative activity of scientists, industrial leaders and government officials, which can be applied to reduce the human-induced global warming and ozone depletion.
Term Paper # 8. Remarks on the Impacts of Climate Change:
Since the birth of the earth about 4600 m.y. ago from dusts or nebula, it took about 200 m.y. to form the primitive crust, by cooling and condensation of the ‘boiling ball’ of molten rock material. The first rock to form in the hot early earth was igneous and when the climate became cooler, suitable for weathering, sedimentary rocks were formed. An igneous rock, crystallized at depth (called plutonic rock), is coarse grained while the same magma when reaches the earth’s surface gives rise to a fine grained rock (called volcanic rock).
This is due to the change in environmental condition of crystallization of magma. The stepwise change of climatic conditions (temperature, precipitation etc.) from hot earth to relatively cool earth during the Archean facilitated more weathering of rocks eventually leading to increasing amount of different types of sedimentary rocks. The accumulation of some amount of free oxygen in the atmosphere and photosynthesis of algae in the ocean caused precipitation of Banded Iron Formation (BIF, chemical sediment) during the Archean.
The appearance of adequate free oxygen in the atmosphere, i.e., oxidizing condition, favoured formation of Red beds and evaporites in the Proterozoic time (2500 – 570 m.y.). The warm climate caused evaporation of inland sea water adjacent to coastal zone as a result of which direct precipitation of evaporate mineral deposits (e.g., gypsum, halite) took place. The warm, humid and oxidizing conditions facilitated formation of arkose and warm-water carbonate rocks which are present in Proterozoic and Paleozoic rock records.
In the glacial climate, the movement of glacier produces a typical rock, till, which is composed of highly unsorted boulder to clay-sized particles. Varve typically formed in glacial lake due to seasonal fluctuation. Such glacial boulder beds or tills and verves have been occasionally recorded from Precambrian to Pleistocene time.
Palaeosoil was formed by weathering of rocks under suitable climatic conditions as we see today. The palaeosoils, residual mineral deposits and supergene enrichment mineral deposits have been recorded from different ages of earth’s history, testifying the impact of palaeoclimate on the formation of such deposits.
The stratigraphic records of sedimentary rocks indicate that palaeoclimatic conditions controlled not only the characters of the palaeolives (now preserved as fossils), but also their distribution on the earth. For example, the warm, humid climatic conditions (containing high CO2 in the atmosphere) facilitated development of luxuriant Glossopteris flora and rich coal deposits (under swampy reducing environment) in Permian of the lower Gondwana regions.
Glossopteris became almost extinct in the Triassic when the climate changed to arid condition giving rise to the appearance of Dicroidium flora which, in turn, was replaced by Ptilophyllum flora in the Jurassic Gondwana due to the reappearance of warm, humid climate.
The warm climate favoured the appearance and development of some organisms such as hermatypic hexacorals, land-living reptiles, marine reptiles, plesiosaurus and robust labyrinthodont amphibians. The fossil Lystrosaurus present in Triassic and Jurassic rocks thrived in tropical to subtropical climates of the world. It was the impact of warm moist climate which facilitated the development of giant dinosaurs (reptilian fauna) of Late Jurassic.
The desert has been formed by the scanty rainfall but it has extended due to human-induced causes at the root of which lies the population explosion. The rocks in the desert climate underwent and are undergoing weathering mainly by physical process facilitated mainly by temperature variation between day and night over thousands of years. The landscape changes in the desert (sand dimes, ripple marks on the sand, barchans, etc.) take place mainly by wind action.
After the appearance of life in the Archean, several events of mass extinction took place in the geological history. The most severe mass extinction took place during Permo-Triassic boundary period (P/T) although much more attention has been drawn by Cretaceous-Tertiary boundary (K/T) period mass extinction. Although several theories have been proposed for mass extinctions (for example, bolide impact, volcanism, global warming/cooling, change in environment in the ocean) the effective cause was the climate change.
Glacial climates have repeatedly affected the earth since Late Archean (~3000 my. – 2500 my.) to Pleistocene (~1.8 my. ago). The Milankovitch Cycles are thought to be the main cause. The glacier movement changes the landforms of the Earth, for example, the V-shaped river valley is changed to U-shaped valley. Besides, the glaciers give rise to dome-shaped and channel-shaped landscapes as well as continental size ice-sheets (e.g., Antarctic and Greenland) and ice-caps occupying flat-topped mountains – all depending upon the topography of the original landform.
In polar and semi-polar regions, glacial climate forms perennially frozen ground called permafrost (av. annual temperature < -2°C; for example, Alaska). The impact of glacial ice has been disastrous for human lives (for example, Titanic disaster of 1912 and Peru ice-avalanche of 1970). The sub-glacial volcanism may cause mudflows (‘lahar’) bringing about destruction of property and human lives.
The impacts of Pleistocene glaciation are:
(i) Southward expansion of Arctic conditions in USA and northern Europe,
(ii) Fall of sea-level at least up to 75 m during maximum ice coverage,
(iii) Extensive development of glacial landforms,
(iv) Change of old drainage channels,
(v) Formation of great lakes of North America and
(vi) Transportation of fertile top soil from over the bed rock of many areas to elsewhere.
Global warming and cooling is a natural phenomenon throughout the geological history of the earth. The earth was much warmer in Late Cretaceous (65 m.y. ago) to Early Tertiary time than today. The clear trend of increasing global temperature during the last 150 years, its impacts on the geological system (e.g. sea-level rise, retreat of glaciers) observed over quite some years and predictions from different models regarding the probable disastrous effects in the near future have been of serious concern all over the world.
The estimated lowest sea-level rise is likely to flood many coastal areas and the highest sea-level rise would cause disaster for most coastal cities where live half of the world’s population. The increasing temperature will cause more rainfall, more expansion of desert, increase in frequency of droughts and thunderstorms, El Ninos and a great change in world hydrological cycle and major impacts on regional water resources.
It is uncertain whether the agricultural crops will increase or decrease. If the increasing trend of global warming continues causing melting of all the glaciers of the Himalayas, it is likely that many glacial lakes of the Himalayas will explode causing floods in the ice melt-fed rivers of the Indo-Gangetic plains subsequently followed by drying of these river beds (because glacial melt water would no longer be available and there is uncertainty in the availability of sufficient rain water) and deforestation of the Himalayas leading to a great change in the ecological system and climatic change in all the surrounding Asian countries.
The main cause of global warming in the last 100 years or so is the emission of increasing amount of greenhouse gases in the atmosphere to meet the demands for comforts of increasing human population. Our immediate task is to take appropriate steps to check emission of greenhouse gases and convince the world leaders to come to a consensus following the advice of IPCC.