Astronomy 123 Homework Assignment Example | Topics and Well Written Essays - 250 words - 1

Astronomy 123 Homework - Assignment Example The shell becomes more massive as it sweeps the surrounding, it, therefore, slows down. The remnants of these explosions can live up to100,000 years, which seems a long duration in terms of astronomical time scale. The most recent supernova experienced in our galaxy was discovered through tracking the remains of its massive explosions. NASA uses Chandra X-ray observation to estimate the frequency with which supernovas explode in the Milky Way Galaxy. NASA estimates that the last supernova occurred almost 140 years ago measured within the period of the earth. Initially, the last supernova had occurred in 1680. Supernovas are, therefore, rare occurrences with only six observed in the earth’s galaxy over a period of 1000 years (Yockey and Hubert 142). The estimate for their occurrence is one supernova for every 25 to 100 years; therefore, it is likely that one may occur soon. The first theory explaining the origin of water talks about volcanic activity. It suggests that when the earth cooled, certain elements that broke apart recombined forming new substances. Two of those elements are hydrogen that broke away from hydrocarbons (for example methane) and oxygen that broke away from iron oxide. Molten magma carried these elements to the surface; they then combined to form water. This however does not seem sufficient to account for 70% of the earth’s surface. Another theory suggests that water was delivered to earth by earth-grazing comets. While the nebulae has water within its remote corners, analysis of this water shows that it is not the same water like that found in the earth’s oceans. The snowball earth hypothesis states that the surfaces of the earth and the ocean were covered with ice across the poles of the equator during periods of extreme cooling about 2.4 billion years ago (Singh 109). Evidence for this hypothesis is found in the ancient rocks that preserve signs of past magnetic field. Additionally, there is a