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Recap the Black Holes Describe the conditions for a stellar black hole to be formed Describe the tidal effects and time dilation near a black hole Describe the X-ray observations of a black hole Describe Hawking’s proposal on white holes Is there any experimental support for this idea ? Discuss the galactic black holes Extra-terrestrial Life Introduction Origin of Life on Earth Characteristics of Life Biological Evolution Extremophiles Life in our Solar System Introduction Astrobiology: interdisciplinary research field on exobiology, the study of planets in the solar system and beyond, space flights, origins of life. Exobiology: the study of organisms that originate outside Earth. It also encompasses SETI. Origin of Life on Earth (I) Chemical Evolution - the process that manufactured molecules and compounds of increasing complexity. Supernovas produced heavy atoms, which were combined to form molecules and compounds, which were subsequently condensed into asteroids, planets and new stars. Recent astrophysical experiments demonstrated the fact that asteroids can contain complex aromatic molecules, which could lead to life under certain physical conditions (the Miller-Urey experiment) Origin of Life on Earth (II) Chemosynthesis 1st phase: hydrocarbon chains formation from ammonia, water and hydrogen (the Miller - Urey experiment). These complex molecules were formed in the air and accumulated in the oceans. Origin of Life on Earth (III) 2nd phase: simple organic molecules under heat bond to create macromolecules peptides proteins, fat molecules, complex sugars) 3rd phase: macromolecules are organized into cells which resemble living things (coacervates). 4th phase: nucleic acids control the reproductive and internal activities of coacervates. 5th phase: natural selection of the cells which can use energy most efficiently and reproduce more rapidly. 6th phase: self-sufficient autotrophic bacteria Characteristics of Life Composed of cells; 1-cell amoeba But viruses do not contain cells and have all the other characteristics of life) Require energy for metabolism and locomotion – ATP molecules Sexual or asexual reproduction Inherit traits from parents (heredity) Respond to stimuli in their environment (light, heat etc) Maintain a state of internal balance (homeostasis) Adapt to their environment and evolve Biological Evolution While chemosynthetic theory explains the development of life, biological evolution explains the origin of millions of life forms. Evolution is the progressive change of genes in a population. The mechanism that weeds out the positive changes from negative changes is natural selection, a concept developed by Charles Darwin. This mechanism will ensure the survival of the fittest. Evolution is slow, gradual change without a clear direction (not towards something better, or from simple to complex). Contrary to popular belief, humans are not on top of the evolutionary ladder; we are just another branch on the bush of life. Extra-terrestrial life can be very different. Extremophiles Extremophiles are organisms which can live in extreme conditions: in caves miles underground, in sulphuric acid, in the hot water heated by submarine volcanoes (tube worms) in the cold of the Antarctic. Humans are limited by the need for oxygen, the boiling and the freezing points of water and the low tolerance for extreme acidity or alkalinity. But life has evolved to fill every possible niche on Earth and this might give an idea about ET. The Habitable Zone As the mass of the star increases the habitable zone moves further from the star. Life in the Solar System A habitable zone is the region around a star where liquid water could exist at the surface. Today only Earth has liquid water at the surface. The size of the planet and the existence of tectonic activities are also important. Too small planets do not hold onto an atmosphere, while too large planets will pull it to the surface. Life could exist outside the habitable zone but we expect that it is very different from the life on Earth. Life on Mars (I) Mars had some tectonic activity long time ago (we can still see the volcanoes). The CO2 released by its volcanoes heated the atmosphere and allowed for water to exist on the surface. Images from Mars show riverbeds as evidence that it had water in the past. Because of a very low density of the atmosphere Mars cannot retain heat and today it has an average temperature of –60 degrees and no liquid water at the surface. The Pathfinder mission to Mars initiated the examination of soil around riverbeds. Life on Mars (II) Meteorites were found as coming from Mars with signs of life In 1996 NASA announced that a small meteorite (ALH84001) discovered in Antarctica contains globules of carbonates, formed by the decompo-sition of bacteria on Mars. Other scientists formulated other theories about the creation of these carbonates (they used the fact that the size of these bacteria was too small) and the debate is still open. Panspermia is a theory which supports the idea that life is spread through meteorites. Life on Venus Like Mars, Venus has an atmosphere of CO2, but unlike Mars its atmosphere is extremely dense. Being closer to the Sun, Venus has higher temperatures, which not only evaporates water but also causes volcanoes activity. This leads to CO2 and the greenhouse effect which further increases the surface temperature (average 482 degrees !). On Earth we have biogeochemical cycles (carbon and nytrogen) which stop the greenhouse effect from happening (but industrialization threatens this equilibrium) Life on Europa and Titan There is strong indirect evidence that Europa (one of the moons around Jupiter) has an ocean under a thick crust of ice. We know that deep sea volcanic vents can generate tube worms. But Europa ocean has little sources of energy. Titan (one of Saturn’s moons) has liquid methane and ethane, solid ice, and smog particles raining from space. Life there would be very different from life on Earth.
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