Big bang theory a. Explain how scientific discoveries have changed our understanding of that scientific concept or phenomenon over time.

b. Include three specific, sequential examples that support your explanation of how your chosen concept has changed over time based on new knowledge and understanding.
1950-1965
Big Bang theory could explain both the formation and the observed abundances of hydrogen and helium, whereas the Steady State could explain how they were formed, but not why they should have the observed abundances. However, the observational evidence began to support the idea that the universe evolved from a hot dense state. In addition, the discovery of the cosmic microwave background radiation in 1965 was considered the death knell of the Steady State, although this prediction was only qualitative, and failed to predict the exact temperature of the CMB. (The key big bang prediction is the black-body spectrum of the CMB, which was not measured with high accuracy until COBE in 1990). After some reformulation, the Big Bang has been regarded as the best theory of the origin and evolution of the cosmos.
1970-1980
most cosmologists accepted the Big Bang, but several puzzles remained, including the non-discovery of anisotropies in the CMB, and occasional observations hinting at deviations from a black-body spectrum; thus the theory was not very strongly confirmed.
1990-present time
This showed that earlier claims of spectral deviations were incorrect, and essentially proved that the universe was hot and dense in the past, since no other known mechanism can produce a black-body to such high accuracy. Further observations from COBE in 1992 discovered the very small anisotropies of the CMB on large scales, approximately as predicted from Big Bang models with dark matter. From then on, models of non-standard cosmology without some form of Big Bang became very rare in the mainstream astronomy journals.

Chernobyl disaster a. Discuss the social or historical context in which the event occurred. b. The disaster began during a systems test on Saturday, 26 April 1986 at reactor number four of the Chernobyl plant, which is near the city of Pripyat and in proximity to the administrative border with Belarus and the Dnieper river. There was a sudden and unexpected power surge, and when an emergency shutdown was attempted, an exponentially larger spike in power output occurred, which led to a reactor vessel rupture and a series of steam explosions. These events exposed the graphite moderator of the reactor to air, causing it to ignite.[3] The resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area, including Pripyat. The plume drifted over large parts of the western Soviet Union and Europe. From 1986 to 2000, 350,400 people were evacuated and resettled from the most severely contaminated areas of Belarus, Russia, and Ukraine.[4][5] According to official post-Soviet data,[6][7] about 60% of the fallout landed in Belarus. c. The accident raised concerns about the safety of the Soviet nuclear power industry, as well as nuclear power in general, slowing its expansion for a number of years and forcing the Soviet government to become less secretive about its procedures.[8][notes 1] The government coverup of the Chernobyl disaster was a "catalyst" for glasnost, which "paved the way for reforms leading to the Soviet collapse".[9] d. Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. A report by the International Atomic Energy Agency examines the environmental consequences of the accident.[7] Another UN agency, UNSCEAR, has estimated a global collective dose of radiation exposure from the accident "equivalent on average to 21 additional days of world exposure to natural background radiation"; individual doses were far higher than the global mean among those most exposed, including 530,000 local recovery workers who averaged an effective dose equivalent to an extra 50 years of typical natural background radiation exposure each.[10][11][12] Estimates of the number of deaths that will eventually result from the accident vary enormously; disparities reflect both the lack of solid scientific data and the different methodologies used to quantify mortality – whether the discussion is confined to specific geographical areas or extends worldwide, and whether the deaths are immediate, short term, or long term. e. Thirty one deaths are directly attributed to the accident, all among the reactor staff and emergency workers.[13] An UNSCEAR report places the total confirmed deaths from radiation at 64 as of 2008. The Chernobyl Forum predicts the eventual death toll could reach 4,000 among those exposed to the highest levels of radiation (200,000 emergency workers, 116,000 evacuees and 270,000 residents of the most contaminated areas); this figure is a total causal death toll prediction, combining the deaths of approximately 50 emergency workers who died soon after the accident from acute radiation syndrome, nine children who have died of thyroid cancer and a future predicted total of 3940 deaths from radiation-induced cancer and leukemia.[14] f. In a peer reviewed publication in the International Journal of Cancer in 2006, the authors of which, following a different conclusion methodology to the Chernobyl forum study, which arrived at the total predicted, 4000, death toll after cancer survival rates were factored in, the paper stated, without entering into a discussion on deaths, that in terms of total excess cancers attributed to the accident:[15] g. The risk projections suggest that by now Chernobyl may have caused about 1,000 cases of thyroid cancer and 4,000 cases of other cancers in Europe, representing about 0.01% of all incident cancers since the accident. Models predict that by 2065 about 16,000 cases of thyroid cancer and 25,000 cases of other cancers may be expected due to radiation from the accident, whereas several hundred million cancer cases are expected from other causes. h. Also based upon extrapolations from the linear no-threshold model of radiation induced damage, down to zero, the Union of Concerned Scientists estimates that, among the hundreds of millions of people living in broader geographical areas, there will be 50,000 excess cancer cases resulting in 25,000 excess cancer deaths.[16] i. For this broader group, the 2006 TORCH report, commissioned by the European Greens political party, predicts 30,000 to 60,000 excess cancer deaths.[17] In terms of non-scientific publications, two affiliated with the anti-nuclear advocacy group Greenpeace, have been released, one of which reports the figure at 200,000 or more.[18] j. The Russian founder of that regions chapter of Greenpeace, also authored a book titled Chernobyl:Consequences of the Catastrophe..., which concludes that among the billions of people worldwide who were exposed to radioactive contamination from the disaster, nearly a million premature cancer deaths occurred between 1986 and 2004.[19] The book however has failed the peer review process,[20][21] five reviews were published in the academic press, with four of them considering the book severely flawed and contradictory, and one praising it while noting some shortcomings. The review by M. I. Balonov published by the New York Academy of Sciences concludes that the value of the report is negative, because it has very little scientific merit while being highly misleading to the lay reader. It also characterized the estimate of nearly a million deaths as more in the realm of science fiction than science.[22]

On 26 April 1986, at 01:23 (UTC+3), reactor four suffered a catastrophic power increase, leading to explosions in its core. This dispersed large quantities of radioactive fuel and core materials into the atmosphere[23]:73 and ignited the combustible graphite moderator. The burning graphite moderator increased the emission of radioactive particles, carried by the smoke, as the reactor had not been encased by any kind of hard containment vessel. The accident occurred during an experiment scheduled to test a potential safety emergency core cooling feature, which took place during a normal shutdown procedure.

k. Discuss the impact that your chosen historical event has had upon our scientific understanding of an aspect of the natural world. l. Residual radioactivity in the environment m. Rivers, lakes and reservoirs n. Earth Observing-1 image of the reactor and surrounding area in April 2009 o. The Chernobyl nuclear power plant is located next to the Pripyat River, which feeds into the Dnieper reservoir system, one of the largest surface water systems in Europe, which at the time supplied water to Kiev's 2.4 million residents, and was still in spring flood when the accident occurred.[114]:60 The radioactive contamination of aquatic systems therefore became a major problem in the immediate aftermath of the accident.[115] In the most affected areas of Ukraine, levels of radioactivity (particularly from radionuclides 131I, 137Cs and 90Sr) in drinking water caused concern during the weeks and months after the accident,[115] though officially it was stated that all contaminants had settled to the bottom "in an insoluble phase" and would not dissolve for 800–1,000 years.[114]:64 Guidelines for levels of radioiodine in drinking water were temporarily raised to 3,700 Bq/L, allowing most water to be reported as safe,[115] and a year after the accident it was announced that even the water of the Chernobyl plant's cooling pond was within acceptable norms. Despite this, two months after the disaster the Kiev water supply was abruptly switched from the Dnieper to the Desna River.[114]:64–5 Meanwhile, massive silt traps were constructed, along with an enormous 30m-deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River.[114]:65–7 p. Bio-accumulation of radioactivity in fish[116] resulted in concentrations (both in western Europe and in the former Soviet Union) that in many cases were significantly above guideline maximum levels for consumption.[115] Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1,000 Bq/kg in the European Union.[117] In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the years after the accident.[116] q. In small "closed" lakes in Belarus and the Bryansk region of Russia, concentrations in a number of fish species varied from 100 to 60,000 Bq/kg during the period 1990–92.[118] The contamination of fish caused short-term concern in parts of the UK and Germany and in the long term (years rather than months) in the affected areas of Ukraine, Belarus, and Russia as well as in parts of Scandinavia.[115] r. Groundwater s. t. u. Map of radiation levels in 1996 around Chernobyl v. Groundwater was not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away long before they could affect groundwater supplies, and longer-lived radionuclides such as radiocaesium and radiostrontium were adsorbed to surface soils before they could transfer to groundwater.[119] However, significant transfers of radionuclides to groundwater have occurred from waste disposal sites in the 30 km (19 mi) exclusion zone around Chernobyl. Although there is a potential for transfer of radionuclides from these disposal sites off-site (i.e. out of the 30 km (19 mi) exclusion zone), the IAEA Chernobyl Report[119] argues that this is not significant in comparison to current levels of washout of surface-deposited radioactivity. w. Flora and fauna x. y. z. After the disaster, four square kilometers of pine forest directly downwind of the reactor turned reddish-brown and died, earning the name of the "Red Forest".[120] {. After the disaster, four square kilometers of pine forest directly downwind of the reactor turned reddish-brown and died, earning the name of the "Red Forest".[120] Some animals in the worst-hit areas also died or stopped reproducing. Most domestic animals were removed from the exclusion zone, but horses left on an island in the Pripyat River 6 km (4 mi) from the power plant died when their thyroid glands were destroyed by radiation doses of 150–200 Sv.[121] Some cattle on the same island died and those that survived were stunted because of thyroid damage. The next generation appeared to be normal.[121] |. A robot sent into the reactor itself has returned with samples of black, melanin-rich radiotrophic fungi that are growing on the reactor's walls.[122] }. Of the 440,350 wild boar killed in the 2010 hunting season in Germany, over 1,000 were found to be contaminated with levels of radiation above the permitted limit of 600 bequerels per kilogram, due to residual radioactivity from Chernobyl.[123] Germany has "banned wild game meat because of contamination linked to radioactive mushrooms".[124] ~. The Norwegian Agricultural Authority reported that in 2009 a total of 18,000 livestock in Norway needed to be given uncontaminated feed for a period of time before slaughter in order to ensure that their meat was safe for human consumption. This was due to residual radioactivity from Chernobyl in the plants they graze on in the wild during the summer. 1,914 sheep needed to be given uncontaminated feed for a period of time before slaughter during 2012, and these sheep were located in just 18 of Norway's municipalities, a decrease of 17 from the 35 municipalities affected animals were located in during 2011 (117 municipalities were affected during 1986).[125] . The after-effects of Chernobyl were expected to be seen for a further 100 years, although the severity of the effects would decline over that period.[126] Scientists report this is due to radioactive caesium-137 isotopes being taken up by fungii such as Cortinarius caperatus which is in turn eaten by sheep whilst grazing.[125] . The United Kingdom was forced to restrict the movement of sheep from upland areas when radioactive caesium-137 fell across parts of Northern Ireland, Wales, Scotland and northern England. In the immediate aftermath of the disaster in 1986, a total of 4,225,000 sheep had their movement restricted across a total of 9,700 farms, in order to prevent contaminated meat entering the human food chain.[127] The number of sheep and the number of farms affected has decreased since 1986, Northern Ireland was released from all restrictions in 2000 and by 2009 369 farms containing around 190,000 sheep remained under the restrictions in Wales, Cumbria and northern Scotland.[127] The restrictions applying in Scotland were lifted in 2010, whilst those applying to Wales and Cumbria were lifted during 2012, meaning no farms in the UK remain restricted because of Chernobyl fallout.[128][129] . The legislation used to control sheep movement and compensate farmers (farmers were latterly compensated £1.30 per animal to cover additional costs in holding animals prior to radiation monitoring) was revoked during October and November 2012 by the relevant authorities in the UK.[130]

. Include two specific examples that support your analysis of how this event added to or changed our understanding of science in the natural world.

Effect on the natural worldAccording to reports from Soviet scientists at the First International Conference on the Biological and Radiological Aspects of the Chernobyl Accident (September 1990), fallout levels in the 10 km zone around the plant were as high as 4.81 GBq/m². The so-called "Red Forest" of pine trees killed by heavy radioactive fallout lay within the 10 km zone, immediately behind the reactor complex. The forest is so named because in the days following the accident the trees appeared to have a deep red hue as they died due to extremely heavy radioactive fallout. In the post-disaster cleanup operations, a majority of the 4 km² forest was bulldozed and buried. The site of the Red Forest remains one of the most contaminated areas in the world. However, it has proved to be an astonishingly fertile habitat for many endangered species. | | | | WildlifeIn marked contrast to the human cost, the evacuation of the area surrounding the plant has created a lush and unique wildlife refuge. In the 1996 BBC Horizon documentary 'Inside Chernobyl's Sarcophagus', birds are seen flying in and out of large holes in the structure itself. It is unknown whether fallout contamination will have any long-term adverse effect on the flora and fauna of the region, as plants and animals have significantly different and varying radiologic tolerance compared with humans. Some birds are reported with stunted tail feathers (which interferes with breeding). However, it seems that the biodiversity around the massive radiation spill has increased due to the removal of human influence (see the first hand account of the wildlife preserve below). Storks, wolves, beavers, and eagles have been reported in the area. There are reports of mutations in some plants in the area, leading to unsubstantiated tales of a "forest of wonders" containing many strangely mutated plants. Specifically, some trees have weirdly twisted branches that do not reach for the sky.See also | | |

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