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Lectures 1-3.docx

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Tony Davis

Lecture #1: Environment and Environmental changes. • Environment= climate and environmental changes= global changes • the environment covers all of the ambient influences in the physical, biological, and human world • physical world involves the atmosphere lithosphere hydrosphere • the biosphere is contained by these element of physical environment and there interaction • Our atmosphere is composed mostly of N (78%) and O (20%). It produces a modest greenhouse effect because of small, but significant concentrations of CO2, CH4 and other gasses • Our hydrosphere is unique in our solar system. Water can exist in gaseous, liquid and solid forms and readily exchanges between the three states. Energy exchanges accompany changes in state. • Our lithosphere is very dynamic with a hot differentiated interior that drives plate tectonics. • Our biosphere is comprised of the plants and animals that we see, but also contains huge numbers of microbes, the most successful and persistent of Earth’s biota. These are essential to biogeochemical cycles (e.g. the N cycle) and directly and indirectly influence climate. • That there have been large and essentially continuous environmental changes throughout geologic time. • That those changes have been natural, and until very recently been without human influence. • That hominids/hominins evolve some 4 million years ago, but appear to have had little to modest environmental impact until the Holocene, the last 10,500 years. • Throughout most of geologic time the Earth was much warmer than it is today – it had a much larger greenhouse effect. Its geography has changed constantly. • The biomes that we are familiar with – the boreal forest, prairie grasslands, tundra, etc. are recent phenomena. • The ‘normal’ warm world is mostly tropical/subtropical. Forests extended into polar regions What drives the earth systems? • Two major controls both involve energy • The first is generated in the earths interior this determines the place and time for an earthquake or volcano and controls critical chemical cycles, notably the carbon cycle. The package is called plate tectonics. •other source of energy is external- solar radiation it has changed through time and moves at a range of temporal scales therefore the solar energy impacts the Earth's system not only by determine the amount emitted but how that energy being processed by the atmosphere and the Earth's system- Here we see energy one and energy two interacting together • How does it impact the earth system ? It is not only determined by the two systems ( e.g volcanoes and the climate relationship between the two and the effects it had on the climate Systems and there behaviours • The earth's environment can often be considered a large system- the consequence of the interactions between huge number of subsystems • all systems input process and output system ( input energy into the earth and them output energy ) • Open (output) systems exchange both energy and matter, while closed systems are open for energy, but closed for matter. • another subsystem is a closed system hydrologic it holds energy •For Example: the Earth’s energy budget is open. It has inputs (mostly solar) and outputs. The hydrosphere, a subsystem, is essentially closed. It’s driven by energy (open), but the amount of water in the Earth system is finite (closed). Small subsystems – a lake, a forest, a field,etc. are open. Feedback and Equilibrium • The behaviour of systems is determined by feedback. In many natural systems, the interaction of physical and biological variables tends to keep the system in some general balance or equilibrium. These dampening effects are called negative feedback because if one component changes it may add a positive feedback e.g. energy input to the Earth system is uneven. There’s a surplus in the Tropics and a deficit in high latitudes. The oceanic and atmospheric circulations act as negative feedback to transfer energy from areas of surplus to areas of deficit. Positive feedback Changes in one or more components in the system may produce positive feedback and induce changes in the behaviour of that system. e.g. global warming is generally attributed to changes in the proportion of greenhouse gasses – a consequence of fossil fuel burning, deforestation, etc. • In time there may often be a steady state equilibrium --> theres no major disruption that goes on here however there may show a trend which is called dynamic equilibrium •In part, the ability of a system to maintain equilibrium depends on its resilience. In general, complex systems are more resilient than simple ones (natural vs. anthropogenic systems). Lecture #2: Plate Tectonics • there are two major things that drive the earth one is solar energy the other is plate tectonics • In readings 2 and 3 you will see that the segment has a general treatment of plate tectonics and secondly consider volcanic activity and its real and potential impacts on society • Plate tectonics were called continental however it is much more than rafting continents it involves the creation and recycling of the earth;s crust and associated with tectonics and volcanic activity • This has been going on as long as the Earth's has had a crust about 4 billion years • The latest ‘cycle’ began with the breakup of a supercontinent called Pangaea about 250 MYBP. It is a continuous process with no real beginning or end. Why is the Crust so mobile? • the reason the crust is so mobile is because the serious of large currents in Mantel ( the Mantel Structure diagram ) it is kept moulded in the inner solar energy • The Core of the North American plate is the Canadian Shield in Africa, South America are mostly shielded it is in these areas that we find the oldest rocks Seafloor Spreading • As you go away from the centre of the earth the rocks gets old and the spreading process begins • we can measure then through satellite navigate which son which shows us the pattern of the seafloor spreading ( this is the plate tectonics spreading ) • Therefore as this is occurring the oceans crust is being recycled • In the past of Geography continents were not tog together the occurrence of Pangea made them closer Plate Tectonics and Volcanism • they appear in separate places usually in subduction zones Mountains and Plate Tectonics • related to plate movements and continents drifting due to Pangea drifting example: Hamilayes • therefore with this occurring more mountains forming Earthquake's and Volcanism Activity • Islands are being created in the hot spots the Haiiwan hotspot Impact of Plate Tectonics and Earth Environment • changes global geography by the agglomeration and dispersal of continental masses • As soon as you block something It changes global topography mostly by mountain building. It exerts a major control on global climate on a range of time scales. It controls the global carbon cycle hence the size of the Earth’s Greenhouse Effect • it does this through a) changing the locations of continents , changing their mass and topography and influencing atmospheric chemistry • Continental location and topography determine the patterns of atmospheric circulation. • They also exert a major control on oceanic circulation. Atmospheric Circulation • connected in the changes of water it is chopped up due to continents Plate Tectonics influences Atmospheric chemistry and transparency • this is connected to volcanic activity • overall it will affect the world's air ( dust will get in the way) • Plate tectonics also influences climate through atmospheric chemistry and atmospheric transparency. • Most of this is connected to volcanic activity (to the effects of individual eruptions, and to
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