The Quaternary Period of History - Essay Example

The Quaternary period of history is the most recent of epoch, but it spans ages. Many identify this period with the Ice Age, and the Quaternary is certainly a period that saw the blanketing of the earth with sheets of ice. However, it was not one of complete glaciation, as the period is marked with fluctuations in climate types. During the Quaternary, there have been occasions of higher temperatures occurring across the globe, temperatures comparable to and even higher than those we experience today. In truth, "the hallmark of the Quaternary is the repeated oscillation of the earth's global climate system between glacial and interglacial states" (Walker, 2005, p. 1). In order to accurately gauge the occurrences of the past in preparation for the future, it is necessary to establish a system or a scale of timing of these occurrences. In addition to knowledge of all the operations of the earth, having in mind a specific (or even general) idea of the time that it takes for events to occur gives historians, scientists, and even the man in the street an idea not only of the future impact of actions done today, but also when to expect those effects to materialize. Because of this, many scientists have worked hard at developing different techniques to date the past. Techniques have developed over the years, from those that rely on myth to ones that rely on scientific evidence. The general trend of these techniques as the were developed was to posit an older and older earth. The time for the beginning of the earth was at first "estimated" at about 4 ka BP (Walker, p. 2); now there's evidence of its beginning approximately 15 ba BP (Greene, 2003, p. 347). Though no one technique is conclusive, they counterbalance each other to produce a general timescale concerning the evolution of the earth., These techniques have proved useful in examining the evidence for the geological and climactic activity of the earth during the Late Glacial and Early/Holocene era, and the possibilities for human activity resulting from it. Modern Quaternary science began when Louis Agassiz posited the former existence of a "Great Ice Period" (Walker, p. 3). Later, when scholars got accustomed to the Ice-Period idea, Albrecht Penck of Germany attempted to "estimate the duration of interglacial periods" by measuring the "depth of weathering and 'intensity of erosion' in the northern Alpine region of Europe" (p. 3). Other attempts at gauging the length of periods in the Quaternary include the analysis of laminae, which give evidence about the types of activity of the soil and its vegetation through the analysis of layers of sedimentation in the earth's crust. In this study, this technique is used to analyze the layers of soil existing in the British Isles and make conjectures about what sort of climate or geological occurrence produced them. Looking at the size of the layers also gives an idea of the duration of each phase and sheds light on probable oscillations within each phase. Dendrochronology was developed during the early part of the twentieth century, which uses the analysis (counting) of tree rings to gauge the age of a tree and by extension the age of a period. This kind of measurement is useful in establishing the age of civilizations. This works because "trees within a small region often share the same experiences of good and bad years, with resulting patterns of wide and narrow rings that can be matched from tree to tree, from living trees to dead trees, and even to timber, charcoal, etc., used by human beings" (Calder, 1984, p. 224). Because trees also show, from their rings, the type of weather experienced in a given year, tree-ring analysis has been applied here to the study of the climates experienced during the Holocene epoch. This technique is called dendroclimatology (Walker, p. 3). Tree-ring analysis, though able to give only a comparatively short view into the past, is useful in this study, as the entire Holocene epoch lies just within its range. With the advent of radio-carbon dating came a very important tool in the assigning of time values to events in the past. Insight into the age of objects can be gained by assessing the types of elements with which they are made up. This is based on the general instability of the nucleus of atoms. Over time, a reversal of the effects of nuclear fusion takes place, and higher atomic elements break down to become lower ones. When this occurs, traces are left in the surroundings, and when a full understanding of what has occurred is gained by an expert, he or she is able to determine the time-frame in which it took place. The process is called radio-active decay, in which alpha, beta, or gamma rays, are released, each denoting a different type of decay. This kind of decay gives is useful in "dating rocks, archaeological remains, and other objects" and "has established new timescales for the Earth, life, and human activities" (Calder, 1984, p. 272). This technique is often used in the dating of deposits or fossils (such as hunting equipment or coleoptera) found in the layers of the earth, which give information concerning sea levels, temperature, water type (fresh or saline) and human activity in the British Isles at the time period in question. The vegetation (through palynology), water supply, and contour of the landscape have a lot to do with determining where the people in and around the British Isles would have frequented or settled. In addition, the accessibility of the land (for example, whether it be surrounded by water) the presence of natural bridges, clay, marsh-stability of the ground, all play a part in determining where people would have settled. The techniques above are aimed each at discovering this. Though each technique is subject to a certain degree of error, the multiplicity of techniques available and used in the dating and analysis of the activities work together to form a more detailed view of the time. They give evidence not just of the landscape and how it changed, but also about the migration within and between the Isles, as well as to other parts of Europe. Places examined in this study include Northamptonshire county and the Fens in England, Donegal in Ireland, the Essex coasts, Swansea in South Wales, and Hebrides and northern Isles of Scotland. There are also transient mentions of other locations in the Isles. The sea levels at the Fens appeared to have, on the whole, risen significantly from the Late Glacial through Post Glacial and Holocene periods. Deglaciation occurred at about 10-12 ka BP. Beginning the transition, during the time of the Allerd oscillations, the climate went from cold to warm to cold. The Dryas clays formed with the fast increase in water from the melting glaciers. Peat that now lies underwater about 32-52 metres gives evidence of the accessibility of the submerged land at that early time. The peat deposits at a higher level, therefore, shows that those lower levels became more and more inaccessible, indicating rising sea levels. Clay lies at the base of the strata (approximately 450 metres down) as obtained by data gathered from lakes in this area (National Climactic Data Center). This too points toward a rise in sea level concurrent with a transition from colder to warmer climate. The Northamptonshire county of Britain is often described as a floodplain, and in light of the rise in sea levels characteristic of the epoch, it is possible to see why. The increase in the area's temperature during these times would have made it possible (and probable) that people would desire to frequent the area. The temperature increase also led to a rise in sea level at the rate of about a metre every century, even reaching levels about two feet above the current level (Zeuner, 95). Vegetation increases during the warmer periods, so with the onset of our current interglacial this has taken place in Fenland, as is shown to be true by the levels of extant peat deposits. It would appear that because of the increased vegetation and water supply of the time colonization of the area by man was highly likely. It did in fact occur, according to Tolan-Smith in his article "Radio Carbon Chronology and the Lateglacial and Early Postglacial Resettlement of the British Isles." He states, In terms of human geography, the Pleistocene/Holocene transition in the British Isles was marked by the recolonisation of areas uninhabited during the pleniglacial. Three phases can be identified. The first, which began around 12,500 RCY BP (Radiocarbon Years Before Present), towards the end of the Lateglacial Interstadial (pollenzones 1b, Ic and II), was marked by the rapid and widespread dispersal of human groups into the lowlands of central, southern and eastern England. The second phase, corresponding to the Loch Lomond Stadial and Preboreal (Dryas III and Zone IV) and dating from 10,999 to 9000 RCY BP, was an episode of consolidation with little further spread of settlement. (Abstract). Though it is generally well accepted that the Mesolithic period occurred later in the Holocene epoch, there has been some reason to suspect that it might have begun earlier. The current Cambridgeshire Fens' landscape results from the increased warmth of the Post Glacial period, and is described by Greg Phillips in "An Archaeological Resource Assessment of The Mesolithic in Northamptonshire" as having gone through a process of gradual change from a shifting and unstable braided river system with channels separated by shifting sandbars, probably loaded with silt and eroding wind-blown loess soils at the end of the last glacial, through an anastomosing process where fewer, more stable channels were formed and separated by gravel islands, towards a more stable, channelled flow regime (p. 3). Only the earliest stages of this transition occurred in the early Holocene, and it appears that the Mesolithic groups frequented the plains only later in the epoch. However, some radio-carbon dating of one palaeochannel from the Nene Valley (thought to have the potential of yielding information about Mesolithic culture) produced a time of approximately 9 ka BP. This places it at the late Devensian/Early Holocene period, and makes it possible that humans might have dwelt there at that time (Phillips, 3). The erosive quality of the soil makes it an unlikely candidate for vegetation, though the increase of vegetation often causes the opposite effect on soil. The fact that the soil was loess meant it was quite fertile and probably quite favourable to the development of vegetation. However, the important factor contributing to human habitation appeared to be the river and the opportunities for fishing that it afforded. The gravel lands that lie adjacent to the wetlands and clayey lands seemed to be targeted by the humans as ideal for settling. Their closeness to the wetlands made them more attractive, as economic benefits were to be derived from those sources (Phillips, 3). High water tables give rise to paludification, which is "the process of bog expansion resulting from rising water tables as a consequence of peat growth" (Crawford, et. al, 2002, par. 1) The trees that sprang up could not survive in the bogs, and the peat levels of the Fens give evidence of the widespread existence of these bogs. Humans, preferring terra firma, tend not to live in marshland, as it affords very little accommodation for shelter, not just from the elements, but also predators. The decline in forest cover also would have reduced their options for shelter, and deprived them of all the uses they had found for wood. Therefore, the rapid increase in water levels, though attractive in the sense of providing for the development of rivers and a flourishing marine life, probably also led as much to the discouragement of human settlement in the Early Holocene epoch. Concurrently, there is little evidence of their presence before a possible "stagnation of the sea level during the early Subboreal" (Zeuner, 95). This occurred much later in the Holocene, but produced conditions more optimal for the presence and settlement of man. In Donegal, Ireland, the colonization of plants began in the Late Glacial/Early Holocene stage, beginning with such vegetation as juniper scrub, Empetrum heath, and herb-rich grassland". These plants spread quickly throughout Donegal, though there was a brief interruption during a stadial of the lateglacial period. However, the stadial wore off, and soon the land was dominated by the Empetrum heath (Bennett, 1994, par. 21). Bennett goes on to add that characteristic of the Holocene period was the advent of such trees as birch and hazel, and they made their entrance in waves, according to the text. Later (9-8 ka BP) came such types as oak, elm, and pine (par. 22). Though it would appear that, with an increase in the vegetation of the period, pre-historic man might be inclined to populate the area, the general evidence seems overwhelmingly against occupation of Scotland by the Mesoliths. The date given by Richard Gregory, et. al in the article "Archaeological Evidence for the First Mesolithic Occupation of the Western Isles of Scotland" is 7-6 ka BP for the earliest stage of activity by the Mesoliths (2005, p. 944). In addition, peat and pollen deposits indicate that "blanket peat initiation [] was concurrent with tree invasions and woodland diversification (9000-8200 BP)" (Bennett, 1994, par. 24). This would seem odd, especially if one subscribes unrelentingly to the idea that bogs and forestation are mutually exclusive. This idea Crawford, et. al term a "superficial generalization" (2002, par. 1). They go on to say that forests can indeed be "found on bogs in northern areas but these are usually in regions where the soil is frozen to a considerable depth throughout the winter period and root metabolic activity will therefore be minimal during periods of oxygen deprivation" (par. 2). This may have continued during the Lateglacial, as the temperatures would still have been considerably low. However, as the climate warmed late in the Holocene, the trees did go. As there also appears to be little evidence of human settlement here during the Early Holocene period, it might be inferred that the duration of the stadial was too short to have accommodated evidence of settlement. The earth soil thawed, the trees disappeared leaving the bogs, as indicated by the peat levels (Bennett, par. 24). Evidence for the fluctuation of the sea level during the period has also been found on the Essex coasts, areas close to Swansea in South Wales, and also in North Devon's Bidford Bay. The site at Swansea gives evidence of the fluctuation's occurring during the Boreal epoch. No traces of Early-Holocene occupation are mentioned, though later Neolithic and Bronze age sites occur on the coast of Essex. Zeuner cites the site at Walton-on-the-Naze, which carries soil mainly of the Red Crag and London Clay types. The peninsula's northern half is made up of marshland, and postglacial deposits can be viewed when the tide is low. It goes out approximately two miles from the shore (1958, p. 97). Closer to the marshland, a brown layer covering the earth and caused by weathering goes below the current sea level, and Scrobicularia Clay covers it.1 Zeuner indicates that the weathering layer represents the soil that formed at lower sea levels than experienced on the coast of Essex today. According to reports made by Warren, Piggott, Clark, Burkitt and Godwin in 1936 and quoted in Zeuner, the succession of the deposits in six layers (given from top to bottom, F to A) are as follows: F. At this level is the recent salt marsh or bog, which is now destroyed by wave action. E. The Scrobicularia Clay Layer. This layer is over ten feet thick and goes down approximately three feet under the high-water level. This gives evidence of the rise in sea level because Scrobicularia is unable to live outside of water, so must therefore always reside below the low-water mark. Therefore, in order for this layer to exist, sea levels at that timr, even at low tide, would have had to be higher than that. D. This period left behind "peaty marsh clay" which developed in a "brackish water zone over a salt marsh" (98). The saltiness of the water indicates the transgression of the sea. C. The occupation level follows, which denotes the Mid-Holocene epoch, a later stage than that with which this paper is concerned. B. A clay of light grey colour, softer than London clay, suggestive of estuarine influence. A. London Clay. These layers span ages, showing the diversity and the change of the British landscape over time. The implications for human life would appear to be similar to those quoted before. The extant marshlands of the Walton-on-the-Naze are testimony to the fact that increased sea levels resulting from deglaciation leads to swamps, in which areas humans do not tend to settle. However, the vast differences in the constitution of the layers suggest that the glacial and interglacial stages fluctuated, and conditions were alternately conducive and hostile to human settlement. Reasearch done in Scotland has demonstrated that "in the Hebrides and northern Isles (Orkney and Shetland), large areas that are now treeless [and] hyper-oceanic bogs, once had an extensive cover of birch woodland with Corylus avellana, Salix spp., Populus spp. and Sorbus aucuparia extending to their coastal fringes, while more central and eastern areas may have had stands with more warmth-demanding species". However, rising sea levels of the postglacial epoch, and the formation of the salt marshes gave the initial push toward the current treelessness of the landscape. Also in Scotland, Loch a'Chnuic lies close to the Abernethy forest. The glacial period, the activity of the glaciers resulted in boulder clay and morainic material's being deposited. At the deepest levels of the stratification of the soil is to be found bluish grey clays of a compact consistency. This is believed to come from the late Devensian (Late Glacial) age (National Climactic Data Center). Overlying this, and indicative of the early Holocene period, is an "aquatic pollen assemblage [] characterised by a decline in the abundance of Cyperaceae and Equisetum, and the appearance of a diverse aquatic flora" (NOAA). This too points toward a rise in sea level at the onslaught of that period, and this eventually gave rise to the removal of trees. A decline in the deposition of pollen was noted, which is also concurrent with the findings. Interstadials, like those of the Allerd oscillations early in the Holocene epoch, decreased sea levels and increased the gradient of the lower course of the rivers. In the Thames, the erosion which resulted produced a narrow valley/gorge which was graded down to the actual sea level of the time. Low sea levels can also "be deduced from the presence of buried channels in the lower course of [the] river" (p. 129). These low sea levels would have increased accessibility to the fertile soil created by the loess sanded off by glaciers, and to the vegetation that sprang from that soil. Resulting from the quick rise in sea level at the beginning of the current interglacial period, the Thames evinces aggradation (a building up of its bed. Warm faunas were contained in the gravel sheets which were deposited (Zeuner, 1958, p. 129). This presence of fauna would provide a source of food for humans, who might have travelled there in order to fish for morsels. Then, "when the sea rose again after the termination of the glacial phase, the channel at first became a funnel-shaped estuary but, time permitting, this was filled with deposits of an interglacial character. These channels, some of which reach much below present river-level, are called buried or sunk channels. They are typical of the Thames" (1958, p. 130). The fertile soils created by the erosion of the Thames, along with the fresh water made available by the melting glaciers of the river itself, would attract humans to settle along its banks. This would become increasingly plausible at a time when glaciers were melting, when even more deposits of soil were being made along river banks, and more fresh water was being made available. About the English Channel, Zeuner argues that a breach must have occurred during an earlier glaciation period between the chalk ridge once extending from Dover to Calais. Eem deposits of mullosca found in the North Sea indicate that its water came from the English Channel. However, evidence shows that the action of the waves and the scour of the tides have caused the gap to widen between Dover and Cape Gris Nez. This resulted from the flooding of Postglacial times. At the Lateglacial stage, about 15 ka BP, it might have been possible for humans and animals to have walked across the Channel from Britain to the continent, or vice versa (1958, p. 100). As the glaciers melted at the onset of the current interglacial, however, this movement was gradually curtailed. Zeuner gives as the earliest possible date for the flooding of the Chalk-ridge gap as approximately 9 ka BP. The possible presence of deposits on the floor of the straits (which would now have been eroded by tidal scouring) would result in a later date. He also mentions that the evidence in favour of an earlier date is "substantiated by the absence from Britain of certain Danish late Maglemose types of implements, which indicates that a break in cultural relations had taken place by that time" (1958, p. 101). There is also evidence gained by observing the presence of flatworms on either side of the channel, which indicates that "the freshwater connexion between England and the continent was severed before the [summer] temperature had risen to 16 C." (1958, p. 101). Johnston also corroborates this idea: "At the glacial maximum, most of the present North Sea floor was above sea level, and it has subsequently been covered by water" (1995, p. 61). Whenever the actual time that the strait came into being, people who could not walk across could "ferry across the narrow Straits and reach Britain in calm weather" (Zeuner, 1958, p. 102). However, the trip became slowly but increasingly difficult to make during the Lateglacial/Early Holocene period. With regard to Ireland, Zeuner points out that "the Allerd Oscillation is closely connected with the halt at the Fennoscandian moraines," and the pollen indicates that in Ireland the Mesolithic culture could have existed at about 11 ka BP (p. 106). Evidence suggests that the postglacial climate might have been more congenial than today's for the growth of certain plants. With vegetation increasing, the chance of man's traversing or inhabiting the area also increased, and when the ability to move easily from the continent to Britain did exist, then much migration should have taken place during this Lateglacial/Early Holocene epoch. Though not conclusive, the evidence is strong for the changes in the landscape in the British Isles during the Lateglacial/Early Holocene epoch. It appears that migration and settlement, as a result of this climate change, occurred mainly in England and Ireland, but not in Scotland. For the most part, the threshold of the current interglacial period afforded humans more scope for movement and prosperity on the planet. In addition to this, however, it also provided more aesthetic variety in the landscape. For, throughout the Isles, glaciers did give rise to several U-shaped valleys, which not only contributed and to increased fertility of soil and lusher vegetation, but also to the beauty and attraction of the Isles. References Bennett, K. D. 1994, "Postglacial forest development and decline in western Britain and Ireland." NERC http://www.kv.geo.uu.se/scotland/nercfinrep.txt Calder, Nigel 1984, Timescale: an atlas of the fourth dimension. Hogarth, London. Crawford, R. M. M. Jeffree C. E. and Rees W. G. 2002. Paludification and forest retreat in northern oceanic environments. Annals of Botany. 213-226 http://aob.oxfordjournals.org/cgi/content/full/91/2/213 Greene, Brian 2003, The elegant universe: superstrings, hidden dimensions, and the quest for the ultimate theory. Vintage, New York. Gregory RA, Murphy EM, Church MJ, Edwards KJ, Guttmann EB, Simpson DD 2005 "Archaeological evidence for the first Mesolithic occupation of the Western Isles of Scotland" The Holocene, vol. 15. pp. 944-950. Johnston, Paul 1995, "The role of hydro-isostasy for Holocene sea-level changes in the British Isles." Quaternary International. vol. 124, 61-70. http://www.sciencedirect.com/science Loch a'Chnuic, (National Climactic Data Center 1993) http://www1.ncdc.noaa.gov/pub/ data/paleo/paleolimnology/lakelevels/europe/eu5.txt Phillips, Greg, "An archaeological resource assessment of the Mesolithic in Northamptonshire" East Midlands Archaeological Research Framework, 1-7. http://www.le.ac.uk/archaeology/research/projects/eastmidsfw/pdfs/ 10nhmeso.pdf#search='fenland%20and%20settlement%20holocene'Scrobicularia Plana. Peppery Furrow Shell: Scrobicularia Plana. The Marine Life Information Network for Britain and Ireland. 2005. Tolan-Smith, Christopher 1998, "Radio carbon chronology and the Lateglacial and Early Postglacial resettlement of the British Isles", Quaternary International. vol. 49-50, pp. 21-27. http://www.sciencedirect.com/science Walker, Mike 2005, Quaternary dating methods. John Wiley, West Sussex. Zeuner, Frederick E. Dating the past: an introduction to geochronology. Butler and Tanner, London. Read More