AST 248: The Search for Life in the Universe

1. Describe the development that freed living systems from its dependence on the limited information storage capacity of DNA. Development of the nervous system and brain.
2. Suppose a 10 km radius asteroid impacts the Earth, is pulverized, and its mass is spread uniformly over the Earth's surface. How thick a layer would be produced? Equate the volumes of the spherical shell on the Earth's surface with that of the asteroid. Volume of spherical shell is 4&pi R_E² d, where R_E is the Earth's radius and d is the shell thickness. Volume of asteroid is 4&pi R³/3 where R is the asteroid radius. Equating these and solving for d one finds d = R³/3R_E² = 10³/(3 x 6400²) km = 8.1 x 10^-6 km = 8.1 mm.
3. Why are craters produced by impacts from space, even if they impact tangentially, overwhelmingly circular? The impact energy is dominated by kinetic energy, which typically will be hundreds of times larger than the maximum chemical energy that might be released with the impactor is heated (estimated as the TNT equivalent).
4. Approximately, an explosion of about how many megatons of TNT would be necessary to produce global effects on the environment? At least 10,000 MT, but less than 10,000,000 MT.
5. If a long lead time was available, what would be the easiest way to deflect a potential impacting object out of Earth's path? Use the radiation pressure in sunlight.
6. Why is a water/carbon chemistry basis for life expected to be universal? Carbon is relatively abundant and is versatile - it shares up to four electrons, and easily forms long molecular chains (polymers). No other element, even silicon, can match these properties. Water is chemically simple, is abundant, is a liquid over a wide temperature range, dissolves a wide variety of substances including organic molecules, and has a relatively large surface tension.
7. Give an example of convergent evolution: name the animals/plants involved and the feature involved.There are many examples given in the notes, like dolphins, salmon and icthyosaurs (fins), opposums, chameleons, sea horses, binturongs, kinkajous, anteaters, phalangers and monkeys (grasping tails). I'm sure there are many others to be found online.
8. What is the difference in approaches taken by artificial life compared to genetic modification to create the simplest living organisms?Artificial life takes a bottom-up approach while genetic modification takes a top-down approach, i.e., with artificial life you keep adding components until you achieve life, with living systems, you delete genes until the system is no longer alive.