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CHAPTER 1 GROTZINGER, JORDAN, PRESS & SIEVER, Earth Scientists study: rocks the earth the moon the physical evidence for the solar system chemistry of the solar system physics of earthquakes past biology The main difference between Earth Science and the rest of the sciences (except for astrophysics) is the use of “DEEP TIME”. For us a million years passes like a 15-minute smoke-break. Geological processes can take place more slowly than people can notice. But because they run for extremely long periods of time their effects are great. Water recharge in Baton Rouge takes 1000 years Climate change has been accelerated by CO2 emissions over the past 100 years. The Scientific Method Fig. 1.1 The Scientific Method •A philosophical approach •A deductive reasoning approach •Starts with numbers… trends…. Patterns…. i.e. OBSERVATIONS •Explains observations using one or several reasons, i.e. HYPOTHESES •Verification that the explanation works by many experts The Scientific Method •If you know the answer already that is not science •Science is a process •Barriers to science are human e.g., greed, dishonesty, fear of change, hunger for power, cultural conditioning... Uniformitariansim “The present is the key to the past” — James Hutton Natural laws do not change but rates and intensity of processes may vary. Some Geologic Events are Slow The Grand Canyon It took more than 250 million years to deposit this sequence of rocks. The rocks at the bottom of the canyon are about 2 billion years old. Fig. 1.2 Some Geologic Events are Rapid Meteor Crater This feature (~2 km across) formed in less than one minute about 50,000 years ago “The chances that a bolide 1-2 km in diameter will hit the earth by 2880 is 1:300” Martian ventifact (NASA) Rivers on Titan NASA Some Geologic Investigations are Microscopic 1 mm Features less than 0.1 mm can give important information about the history of many rocks. Some Geologic Investigations are Microscopic NASA Big Bang Hypothesis 13-14 billion years ago, all matter and energy was concentrated into a single, inconceivabley small (and very dense) point. This hypothesis stems from a mathematical solution to the problem This hypothesis was tested through the Doppler shift in stellar spectrum, which implied that matter was flying apart in all directions throughout the universe The Hubble Telescope Can detect faint light that has travelled for billions of years, …. from the start of the current universe Nebular Hypothesis and the origin of our Solar system •Older than 4.56 billion years ago •Gravity is the cause of “condensation” of the cloud •Cloud contracted WHILE spinning ever faster •H and He are the most common elements •H and He collected to form fusion reactions Nebular Hypothesis and the origin of our Solar system •Fusion is more energetic and atomic fission but requires greater pressures •Hydrogen “fuel” burns to create He Fig. 1.3 Fig. 1.3 Nebular Hypothesis and the origin of our Solar system •Planetesimals (early-stage, immature, small planets) on the periphery of this contracting, spinning dust cloud began to clump together locally. •Denser materials fell closer to the sun •Less dense materials (gases) could escape to greater distances from the sun e,.g., Jupiter floats in water Fig. 1.3 Nebular Hypothesis and the origin of our Solar system •Mercury, Venus, Earth, Mars are called the terrestrial planets Size of the Planets Fig. 1.4 Size and Relief of Venus, Earth, Mars Fig. 1.9 Pre-scientific medicine Humours: yellow bile, black bile, phlegm, blood Methods of treatment like blood letting, forced vomiting and purges were aimed at expelling a harmful surplus of a humour. They were still in the mainstream of American medicine after the Civil War. Other methods used herbs and foods associated with a particular humour to counter symptoms of disease, for instance: people who had a fever and were sweating were considered hot and wet and therefore given substances associated with cold and dry. (Wikipedia, the free encyclopedia, 2006) Origin if the Moon- Science at work OBSERVATION: The Pacific is large? Why so large? Charles Darwin’s great grandson hypothesized that the Moon came from the Pacific Ocean (HYPOTHESIS) Origin if the Moon- Science at work HYPOTHESIS TESTING: Pacific Ocean is 70-200 my old Such an impact would have melted the earth and reset all radioactive clocks to 0 years old about 100 my after the melting. Nebular Hypothesis and the origin of our Moon •Oldest rocks on the moon are 4.47 by •A Mars-shaped bolide hit the earth about 4.5 by Formation of the Moon (about 4.5 billion years ago) Composition of the Earth (70%) •Key earth elements in the crust: Si, O •Key earth elements in the earth: Fe, Si, O Chemical Composition of Earth Whole Earth: Crust: Fe+O+Si+Mg = 93% Si+O+Al = 82% Fig. 1.7 Composition of the Earth •What is responsible for the distribution of light and dense elements by depth? •How did they get there if the Earth was solid? How old is the Earth? How old is the Earth? Younger than the planetesimals 4.56 by How old is the Earth? Older than the moon How old is the Earth? Older than the moon are 4.47 …...but to form by ……… oldest rocks the moon could have started earlier … 4.5 by What was happening between 4.56 and 4.5 by ? •(1) Accretion to create the first earth… a “magma” earth (100 millionyear-period What happened to the Earth at 4.5 by ? •Earth was hit by a giant bolide (before 4.47 by) that remelted it and led to the formation of the moon What was happening between 4.5 and 4.4 by ? •(1)Mainly cooling and differentiation: Gravity pulled the denser materials toward the core when the Earth was still molten Global Chemical Differentiation Fig. 1.6 Earth as a Group of Interacting Systems •Atmosphere, Hydrosphere, Lithosphere, Asthenosphere, Deep Mantle, Inner Core interact •e.g. Volcanic degassing creates warm periods in Earth’s history •The oceans buffer greenhouse gases •The Core’s magnetic field allows migration of fish and birds Major Components of the Earth System Fig. 1.10 END OF CHAPTER 1