ASTR 1000 Lecture Notes - Lecture 13: Terrestrial Planet, Anatomically Modern Human, Milky Way
19 Oct 2016
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1600s: ussher uses biblical genesis to deduce that earth formed on october 23rd, 4004 bc. 1860s: kelvin (20-40 mil years due to molten rock) vs darwin (300 mil years due to species diversity) 1900s: rutherford shows radioactive decay to say that earth must be billions of years old (radioactive decay) Element : defined by number of protons in nucleus. Isotope : different versions of the same element, but different number of neutrons. Radioactivity : unstable nuclei spontaneously change to other nuclei. Each isotope has a characteristic timescale for decay. Half life : time it takes for 50% to decay. Compare radioactive c 14 to stable c 12 (half life = 5730 years) Can provide accurate dates back to 60,000 years (10 half lives) Measure ratio of isotopes to find out how old something is. Milky way galaxy is 12 billion years old. Less dense materials rise to the surface. Anatomy of a (terrestrial planet) is defined by density and composition.
