Free Essay About Take Home Questions
Geology: Take Home Questions
1. Choose two additional Eh-pH diagrams for metals (e.g. Selenium) or other elements (e.g. Iodine) and write clear and concise answers about the mobility (bioavailability) or lack of mobility of the elements chosen, within the human body (you should include the Eh-pH diagrams for the systems chosen). Compare the Eh-pH diagrams you choose to the Eh-pH diagram below, as the figure provided is a good guide to determine which part(s) of your body a particular chemical species is mobile or immobile.
The element Selenium offers an example that is related to solid speciation and solution as impacted by alterations in system redox. A metalloid that exhibits chemical and physical properties, Selenium bears a resemblance to sulfur and presents in inorganic and organic chemical forms. Inorganic organisms encompass selenide, selenite, elemental selenium, and selenate. Organic species encompass methylated compounds, selenoproteins, selenoamino acids, and their products. The speciation of the element is impacted by the redox or acid conditions of the environment. For instance, selenium exists in decreasing hydrogen selenide in the environment and as metal selenides. The element, selenium, is balanced in a decreased environment; however, it can be corroded to selenite and selenate by various microorganisms. A number of bacteria strains have been recognized to aid selenate reduction in soil. Two bacterial processes namely reduction of selenite and selenate and methylation of selenium, have a major impact on the mobility of selenium in the environment. Methylation of selenium and selenium volatilization, results to dissipation of soil selenium to the air. Environmental components including the microbial community, acid, moisture, temperature and organic amendments control the percentage of selenium volatilization from soils. In a flooding situation, a section of the methylated selenium is transported through water, thereby reducing selenium volatilization to the air. The organic amendments to soils documented to promote indigenous microbes to selenium, in which organic substrates added to sediments have been discovered to hasten the selenate reduction and selenite. Interestingly, the more oxidized selenate conveys a 78 of 957 twofold charges at whatever point the pH is higher than around 2. The consequence of this intricacy is that both the speciation and the pH of the water must be considered when endeavoring to remediate the selenium. This was exhibited in ahead of schedule studies centering on coagulation filtration and lime softening, which presumed that neither one of the approaches was compelling for complete selenium evacuation; however, that they could be improved with pH alterations.
Mechanism for selenium decrease by microbes is complicated as it happens under both anaerobic and aerobic situations. Both detoxification and dissimilatory mechanisms are likely. The manifestation of sequential decrease of selenate to selenite and then to Se is recommended after modification of contaminated cells. Selenium in the human body is a critical element assuming a crucial function in the antioxidation framework of the body. It is perceived as an agent to prevent cancer that can synchronize with diverse cell reinforcements, for instance, vitamins C and E and in approaches protecting the cells from free radicals. In this manner, selenium protects a body from disease advancement, cardiovascular sicknesses as well as manly sterility. In addition, selenium plays a part in thyroid hormone digestion system, hinders destructiveness, resistant framework, and backs off the development of AIDS by decreasing the HIV advancement speed. Furthermore, it can decrease the threat of unrestrained premature births. Adjusted material of selenium in nourishment aids because of problems combined with diabetes as well as affects the abhorrence of asthma. By way of free radicals limit selenium curbs destructive influences of radiation. Selenium is vital for legitimate volume of cerebral neurotransmitters as well as reduces epileptic waves at children. Selenium insufficiency is linked with hastening weakness and development of Alzheimer's disease. Selenium impacts in a constructive way the mental health and human personality.
2. Discuss Goldschmidt’s and Pauling’s ideas on bonding, the importance of ionic size, valence, etc. Generally, you will be discussing Goldschmidt’s rules of substitution. Relate this topic to what we have learned in the class about how potentially dangerous elements bond and what affects this can have on human health.
Goldschmidt and Pauling developed a number of guiding principles which made possible the prediction and rationalization of the arrangements of basic ionic solids. Goldschmidt devised three rules to elucidate the element distributions in minerals. The foundation of these instructions is that ionic substitution of a single cation for another will happen with cations of similar charge and size. The next two rules are that cations of minimal charge and size, or higher charge and similar size will specially include into a developing crystal.
Pauling introduced other three rules that govern ionic arrangements. The first is termed as the radius ratio rules. The concept is that the comparative sizes of the ions identify the arrangement implemented by an ionic compound. Pauling suggested certain values for the cation radius ratio to the anion radius as minimal limits for diverse coordination types. However, the radius ratio rules are not correct in their extrapolation of coordination numbers concerning what is often correct. Generally, it overrates the number of cation being coordinated. This system regards ion as incompressible spheres or directionality of the covalent bonding influence possibly performs as crucial function as fitting as the size of ion. The second rule of Pauling is termed as the electrostatic valence rule. It suggests that the ion charge should be balanced by an opposite and equal charge on the ions surrounding it. The third rule suggested by Pauling is that the existence of shared edges of a polyhedron destabilizes an arrangement. Polyhedra join at the corners. Cations deter each other as faces and edges are shared since the distance between cations diminishes. The slightest reduction happens for edge sharing of octahedral, trailed by edge sharing of tetrahedral, and faces sharing of octahedral, and the biggest reduction is for face sharing in tetrahedral, which makes the configuration unfavorable.
The substitution principle expresses that dangerous chemicals must be substituted systematically be less dangerous alternative or alternatives that no dangers can be recognized. Substitution is considered a risk reduction approach in environmental policy as well as in the safety and health legislation of workers. Substitution principle is the advancement of safer substances and practices, that is, both the management and the hazards brought about by the intrinsic characteristics of a substance must be decreased. Substituting dangerous substances as well as processes with less dangerous ones or with alternatives that are non-chemical is broadly recognized as a very efficient approach to minimize, reduce, or even eradicate risks. In addition, substitution of hazardous substances with less risky ones is identified as an optimal manner to overcome the problems of multifaceted chemicals regulations.
3. From the information provided in the course or other sources, put together your version of the history of the planet Earth with emphasis on geological and atmospheric events that influenced the existence of an environment that lead to the creation of life and shaped the present day Earth. The idea here is to have you produce a history of life and evidence for it, e. g. stromatolites are great if you believe the geologists that those layered fossil like things are paleo algal bodies; but are there chemical and isotopic changes that are present in the geological record.
The geological account of Earth traces the enormous events in the history of the Earth according to the geologic time scale, an arrangement of chronological measurement grounded on the study of the Earth’s rock layers. The planet developed billions of years ago by deposit from the nebula, a mass of disk-shaped dust and gas remained from the sun’s formation, which likewise developed the entire solar system.
Earth was molten because of too much volcanism and constant collisions with heavenly bodies. The external layer of the Earth cooled to create a solid layer when water started to accumulate in the atmosphere. As the earth’s surface continued to reshape over millions of years, various continents developed and separated. They travelled and combined to create a supercontinent. The earliest recognized supercontinent started to break apart. The landforms recombined to develop. The Pangaea then broke apart. The current structure of ice ages started millions of years ago then deepened towards the end of Pliocene. The Polar Regions started to undergo more cycles of thaw and glaciation. The final glacial period of the present ice age came to an end thousands of years ago. It prolongs from billions of years ago to the start of the Cambrian Period. It encompasses the Archean, Hadean, and Proterozoic. The Hadean Eon is not officially acknowledged, but it fundamentally signifies the period before there was enough record of substantial solid rocks. Earth was originally melted because of existing volcanism as well as regular collisions with other bodies. Ultimately, the external layer of the Earth cooled to create a solid layer when water started to accumulate in the atmosphere.
During this period, the Earth’s layer cooled enough that continental plates and rocks started to form. A number of scientists believe that since the Earth is hotter, the tectonic activity plate was a lot vigorous compared to how it is today, leading to a greater percentage of recycling of materials made of crust. This may have stopped cratonisation and formation of continent until there is cool down of the mantle and slow down of convection. Others contend that the lithospheric mantle is resilient to subduct and the inadequacy of Archean rocks is a working of tectonic evens and erosion.
After 3.5 billion years, the magnetic field of the Earth was established. The solar wind flux was 100x the sun’s value, so the existence of the magnetic field aided in preventing the atmosphere of the Earth from being stripped away. Nevertheless, the field strength was lesser compared to the present and the magnetosphere was approximately fifty-percent of the contemporary radius. The first recognized glaciations happened during the Proterozoic, one started shortly following the eon. The Phanerozoic Eon is the present age in the geologic period. During this time, continents floated about, ultimately gathered into a single continent referred as Pangaea and then separate into the present continental landforms.
The most-normally acknowledged philosophy is that these occasions were activated by the beginning of an ice age that lasted the stable greenhouse situations. The ice age was perhaps not as enduring as once supposed. The event was heralded by a decrease in distinctive carbon dioxide which selectively exaggerated the low seas where greatest organisms existed. As the southern supercontinent floated, the South Pole shaped it. Indications of ice caps were perceived in Upper Ordovician rock layers of North Africa and northeastern South America.
Eps.berkeley.edu,. (2015). Geology | Earth and Planetary Science. Retrieved 1 April 2015, from http://eps.berkeley.edu/undergraduate/geology
Extremescience.com,. (2015). Geological History of Earth. Retrieved 1 April 2015, from http://www.extremescience.com/earth.htm
Huang, P., Li, Y., & Sumner, M. (2011). Handbook of Soil Sciences. Hoboken: Taylor and Francis.
Jezek, P., Skarpa, P., Losak, T., & Husek, J. (2012). Selenium – An Important Antioxidant in Crops Biofortification. INTECH.
Lalena, J., & Cleary, D. (2010). Principles of inorganic materials design. Hoboken, N.J.: John Wiley.
Lissner, L., & Romano, D. (2011). Substitution for Hazardous Chemicals on an International Level—The Approach of the European Project "SUBSPORT". NEW SOLUTIONS: A Journal Of Environmental And Occupational Health Policy, 21(3), 477-497. doi:10.2190/ns.21.3.l
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