Mussels and other sea life are harmed by asteroid impacts
Thompson 7 [Asteroid Impact Would Devastate Sea Floor Life, Too http://www.livescience.com/1858-asteroid-impact-devastate-seafloor-life.html]
During a global catastrophe, the shrimp and mussels that thrive around these vents may be just as doomed as the rest of us. Creatures such as bacteria, shrimp and snails have flourished around hydrothermal vents, despite the fact that no sunlight reaches to the depths of the ocean floor. Instead, colonies get nutrition from the minerals dissolved in the superheated water that spews out from the vents. Through a process called chemosynthesis, microbes convert the heat and minerals produced by the vents into energy. They then provide food to more complex forms of life, such as mollusks, crustaceans and worms. Scientists had thought that because the food source of the creatures living around the vents was independent from the world above that an event such as a giant asteroid collision, which can kick up a cloud of debris that blocks the sun for months or years, wouldn't affect the vent ecosystems. But new research done by Jon Copley of the University of Southampton indicates that the offspring of some of these creatures grow up away from the life-sustaining vents and depend for food on whatever material sinks down from the sunlit surface waters. In fact, the vent inhabitants time the birth of their offspring with the seasons—even though they cannot see the sun. They time the release of their young to the spring bloom of the microscopic plant life that grows on the ocean's surface—stuff that sinks after it dies.
UV-B radiation damages DNA.
Jeannie Allen in 2001 (Earth Observatory, Ultraviolet Radiation: How It Affects Life on Earth, 09/06/2001, http://earthobservatory.nasa.gov/Features/UVB/, znf)
UV radiation from the sun has always played important roles in our environment, and affects nearly all living organisms. Biological actions of many kinds have evolved to deal with it. Yet UV radiation at different wavelengths differs in its effects, and we have to live with the harmful effects as well as the helpful ones. Radiation at the longer UV wavelengths of 320-400 nm, called UV-A, plays a helpful and essential role in formation of Vitamin D by the skin, and plays a harmful role in that it causes sunburn on human skin and cataracts in our eyes. The incoming radiation at shorter wavelengths, 290-320 nm, falls within the UV-B part of the electromagnetic spectrum. (UV-B includes light with wavelengths down to 280 nm, but little to no radiation below 290 nm reaches the Earth’s surface). UV-B causes damage at the molecular level to the fundamental building block of life— deoxyribonucleic acid (DNA). Electromagnetic Spectrum Electromagnetic radiation exists in a range of wavelengths, which are delineated into major divisions for our convenience. Ultraviolet B radiation, harmful to living organisms, represents a small portion of the spectrum, from 290 to 320 nanometer wavelengths. (Illustration by Robert Simmon) DNA readily absorbs UV-B radiation, which commonly changes the shape of the molecule in one of several ways. The illustration below illustrates one such change in shape due to exposure to UV-B radiation. Changes in the DNA molecule often mean that protein-building enzymes cannot “read” the DNA code at that point on the molecule. As a result, distorted proteins can be made, or cells can die. Diagram of UV Radiation Mutating DNA Ultraviolet (UV) photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent bases bond with each other, instead of across the “ladder.” This makes a bulge, and the distorted DNA molecule does not function properly. (Illustration by David Herring) But living cells are “smart.” Over millions of years of evolving in the presence of UV-B radiation, cells have developed the ability to repair DNA. A special enzyme arrives at the damage site, removes the damaged section of DNA, and replaces it with the proper components (based on information elsewhere on the DNA molecule). This makes DNA somewhat resilient to damage by UV-B. In addition to their own resiliency, living things and the cells they are made of are protected from excessive amounts of UV radiation by a chemical called ozone. A layer of ozone in the upper atmosphere absorbs UV radiation and prevents most of it from reaching the Earth. Yet since the mid-1970s, human activities have been changing the chemistry of the atmosphere in a way that reduces the amount of ozone in the stratosphere (the layer of atmosphere ranging from about 11 to 50 km in altitude). This means that more ultraviolet radiation can pass through the atmosphere to the Earth’s surface, particularly at the poles and nearby regions during certain times of the year. Without the layer of ozone in the stratosphere to protect us from excessive amounts of UV-B radiation, life as we know it would not exist. Scientific concern over ozone depletion in the upper atmosphere has prompted extensive efforts to assess the potential damage to life on Earth due to increased levels of UV-B radiation. Some effects have been studied, but much remains to be learned.
UV-B Radiation Multiple Impacts
Numerous effects of UV-B light: DNA damage, cancer, eye damage, decrease in plankton, and decreased plant growth.
Brien Sparling in 2001 (NASA, Ultraviolet Radiation,5/30/01, http://www.nas.nasa.gov/About/Education/Ozone/radiation.html, znf)
Genetic damage DNA absorbs UV-B light and the absorbed energy can break bonds in the DNA. Most of the DNA breakages are repaired by proteins present in the cells nucleus but unrepaired genetic damage of the DNA can lead to skin cancers. In fact one method that scientists use to analyze amounts of 'genetically-damaging UV-B is to expose samples of DNA to the light and then count the number of breaks in the DNA. For example J.Regan's work at the Florida Institute of Technology used human DNA to find that genetically significant doses of solar radiation could penetrate as far as 9 feet into non-turbulant ocean water. The Cancer link The principle danger of skin cancer is to light-skinned peoples. A 1%decrease in the ozone layer will cause a estimated 2%increase in UV-B irradiation; it is estimated that this will lead to a 4%increase in basal carcinomas and 6%increase in squamous-cell carcinomas.[Graedel&Crutzen]. 90% of the skin carcinomas are attributed to UV-B exposure [Wayne] and the chemical mechanism by which it causes skin cancer has been identified [Tevini]. The above named carcinomas are relatively easy to treat, if detected in time, and are rarely fatal. But the much more dangerous malignant melanoma is not as well understood. There appears to be a correlation between brief, high intensity exposures to UV and eventual appearance (as long as 10-20yrs!) of melanoma. Twice as many deaths due to melanomas are seen in the southern states of Texas and Florida, as in the northern states of Wisconsin and Montana, but there could be many other factors involved. One undisputed effect of long-term sun exposure is the premature aging of the skin due to both UV-A, UV-B and UV-C. Even careful tanning kills skin cells, damages DNA and causes permanent changes in skin connective tissue which leads to wrinkle formation in later life. There is no such thing as a safe tan. Someone on the beach gettin to much sun "There is no such thing as a safe tan" FDA Publication Possible eye damage can result from high doses of UV light, particularly to the cornea which is a good absorber of UV light. High doses of UV light can causes a temporary clouding of the cornea, called 'snow-blindness', and chronic doses has been tenitively linked to the formation of cataracts. Higher incidences of cataracts are found at high elevations,Tibet and Bolivia; and higher incidences are seen at lower latitudes(approaching the equator). Damage to marine life The penetration of increased amounts of UV-B light has caused great concern over the health of marine plankton that densly populate the top 2 meters of ocean water. The natural protective-responce of most chlorophyll containing cells to increased light-radiation is to produce more light-absorbing pigments but this protective responce is not triggered by UV-B light. Another possible responce of plankton is to sink deeper into the water but this reduces the amount of visible light they need for photosynthesis, and thereby reduces their growth and reproduction rate. In other words, the amount of food and oxygen produced by plankton could be reduced by UV exposure without killing individual organisms. There are several other considerations: Ultraviolet levels are over 1,000 times higher at the equator than at the polar regions so it is presumed that marine life at the equator is much better adapted to the higher enviromental UV light than organisms in the polar regions. The current concern of marine biologists is mostly over the more sensitive antarctic phytoplankton which normally would recieve very low doses of UV. Only one large-scale field survey of Anarctic phytoplankton has been carried out so far [Smith et.al _Science_1992] ; they found a 6-12% drop in phytoplankton productivity once their ship entered the area of the spring-time ozone hole. Since the hole only lasts from 10-12weeks this translates into a 2-4%loss overall, a measurable but not yet catastrophic loss. Both plants and phytoplankton vary widely in their sensitivity to UV-B. When over 200 agricultural plants were tested, more than half showed sensitivity to UV-B light. Other plants showed neglible effects or even a small increase in vigor. Even within a species there were marked differences; for example one variety of soybean showed a 16% decrease in growth while another variety of the same soybean showed no effect [R.Parson]. An increase in UV-B could cause a shift in population rather than a large die-off of plants An increase in UV-B will cause increased amounts of Ozone to be produced at lower levels in the atmosphere. While some have hailed the protection offered by this 'pollution-sheild' many plants have shown themselves to be very sensitive to photochemical smog.