February 11, 2016

Why are volcanoes in subduction zones so dangerous?

∙ When we think of volcanoes  subduction zones  

∙ Taiwan  

o Two subduction zones  

o Two faults parallel the subduction zone of the Eurasian Plate o Philippine plate sub ducting under the Eurasian Plate

o Earthquake wasn’t on a subduction zone but instead on a fault  ∙ History of the Earth and history of life  

o Hadean

 Started 4.54 billion years ago  

o Archean

 Started 4 billion years ago  

 Ended 2.5 billion years ago  

o People trying to figure out how old the earth was  

 Looked at the thickness of sedimentary rocks  

∙ 1861  Earth calculated to be 3 million years old  

When did the archean era begin and end?

∙ 1910  discovery of much more sedimentary rocks,  

found to be 1.6 billion years old  

∙ Problems with doing it this way  

o Rates of sedimentation changes  

 1897  Lord Kelvin  interested in heat  

∙ Calculated that it was 24-40 million years old  

∙ Didn’t realize that the Earth has an internal heat  

system  

 John Joly  

∙ Looked at the salt in ocean and the salt that was  

feeding into the rivers

∙ 90 – 100 million years old  

 1905  radioactive decay first used  Rutherford and  

Boltwood  

∙ Dated the oldest rocks that they knew of  

How did we figure out how old the earth is?

∙ Found that it was 500 million years old  Don't forget about the age old question of What is the difference between dna & rna?

 1907  Boltwood  uranium turned into lead  

∙ Dated some uranium containing rocks  

∙ Came up with the date 1.64 billion years old  

∙ Two things happen to the Earth  

o Gravitational compression

 Applied pressure that creates heat  

 Heating up the Earth  leads to heat within the Earth  

 A lot of material starts to melt or partially melt  

o Radioactive decay  

 This leads to an internal heat source  

 A lot of material starts to melt or partially melt

o This allows the earth to start to differentiate  

 This is what gives the Earth its different layers  

 The material that moves toward the center are the denser  and heavier materials  

∙ Like nickel and iron We also discuss several other topics like What are the antioxidant enzymes?

 Lighter materials came out toward the mantle and crust  ∙ Silicate rich  

 Before this differentiation, the surface of the Earth was  probably molten  

∙ Liquid Outer Core  

o The liquid circulates  doesn’t just sit there  

 This sets up an electric field  the geodynamo

 Electric field sets up a dipolar magnetic field  

∙ Magnetic field  

o Polarized, we have a north and a south  

o Magnetite and other magnetized minerals  

 Igneous  

 When it crystalizes, it crystalizes with that magnetic field  ∙ Aligns itself with the magnetic field (points north)  

 If it weathers out and becomes a sedimentary grain

∙ Also orients itself north-south with the magnetic field  of the Earth  

 One way we can go back in time and figure out the  

orientation of the plate  

∙ If it isn’t pointing north, we know how much it has  

rotated  

 Amount of inclination tells you the latitude that the mineral was formed in  

∙ Magnetic inclination  latitude of formation

 Every 4-5 million years the poles reverse themselves  ∙ Not precise, there is some variation  

∙ Reverse magnetism  

∙ Oldest whole rock  Nuvvuagittug Greenstone Belt  If you want to learn more check out What wealth can do is bring leisure, audience, peers, train experts, readers, who place social value?
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o Dates to 4.28 billion years  

o In Quebec  

o Remnants of some of the oldest continental crust on Earth   North American craton  

∙ Oldest minerals  Found in the Naryyer Gneiss

o From Australia  

o Old parts of this Australian craton  

o Inside are some really tough minerals  zircon  

 Taken the zircon out and dated at 4.4 billion years  

 Layers in the zircons show the way it grew

∙ Added layer after layer until it reached its final size

∙ Oceanic crust  

o Begins to differentiate to its more mafic parts and its more felsic  material  

o Felsic material starts to rise and accumulate  

 Becomes continental crust  

∙ Water begins to form  

o Early in Earth history, we have a lot of volcanism going on   Lots of lava but also a lot of gas

 Huge reservoir of gases  

∙ One of these is water vapor  

o Water vapor begins to condense and form water on the surface  ∙ Everything coming onto the surface is coming out of these volcanoes  o Greenstone Belts  

 Oldest rocks  

 Chlorite  causes it to be green  

 Pillow basalts  very mafic We also discuss several other topics like What is an absolute space?

∙ Extruded underwater  

∙ Underwater volcanism that extrudes up and up  

∙ Oldest evidence of water that we know of is 3.8 billion years ago  o Found in Greenland  

o Water and air leave their mark  

o These rocks show evidence that they were deposited by water  ∙ 3.5 billion year old  Australia  

o Shows that the continental crust built up enough  

o Shows that there is now land above sea level  

∙ Atmosphere of our early Earth  

o Chemically aggressive atmosphere  

 Contains water vapor  

 Contains a lot of methane, ammonia, formaldehyde, carbon dioxide and hydrogen cyanide  

 A lot of greenhouse gases coming out of volcanoes  

o Essentially no free oxygen  

 No ozone layer  

 High layer of UV radiation in the air  

o Water and metal oxides were in the oceans  

 This forms acids  

∙ Hydrochloric, sulfuric and others  

∙ pH of these oceans were 2 – 4  

o These are the conditions that early life formed under  ∙ Earliest Life  Don't forget about the age old question of What do conceptual scheme relativists believe?

o Build complex carbon-based molecules  

 Basis for life

 1953  Miller and Urey  

∙ Took some flasks and filled them with water  

∙ Added the gases that they thought should be there  o Ammonia, water vapor, methane, etc.

∙ Added some electrical charge for lightning  

∙ Finally uncorked the flask and found what had  

formed in there  

∙ What they found was long chains of amino acids  o This is what builds proteins  

∙ Found that they could generate these building blocks of life  

 Very easy to generate amino acids  

∙ Amino acids won’t form under free oxygen

 Found that they can make nucleic acids  

∙ Building blocks for DNA and RNA  

o First life

 Originated in the ocean  

 Originated near spreading centers (warm)

 Were chemosynthesizers  

 Possibly happened as early as 3.7 billion years ago  o Greenland Isua Formation  3.7 billion years  

 Found Carbon isotopes  

∙12C : 13C = 100 : 1  

∙ Carbon 12 is preferred by organisms (lighter  

isotopes)  

∙ Biomarker  

 Isoprene chain  

∙ Organic molecules  

∙ Isoprene is used as the cell wall of the most primitive organisms that we know of today  Archea  

o Archeans can live in extreme environments  

 Can live without oxygen  

 Are methanogens  

∙ Can tolerate really hot temperatures  

 These conditions sort of replicate the conditions on early  Earth  

o 3.5 billion years ago  first body fossils in Australia   Fossilized cells that look like a second kind of organisms  called cyanobacteria

 Structures called stromatolites

∙ Structure that are formed by cyanobacteria  

∙ Bacteria lives in shallow water

o Sediment settles on them, bacteria move up,  

sediment settles, bacteria move up, etc.  

o Cyanobacteria  

 Global by 3.5-3.4 billion years  

 Use photosynthesis  

∙ Consumes carbon dioxide in the atmosphere  

∙ By product is free oxygen  

 Over time, this free oxygen builds up and the amount of  free oxygen in the atmosphere starts to go up  

∙ This changes many things  

 Iron  comes in two forms  

∙ Ferrous Iron  soluble in water  

o Stable in reducing conditions (no oxygen)

o Gray or black in color  

∙ Ferric Iron  

o This is what happens in oxidizing environments

o Red, essentially rust  

o Insoluble in water  

 Precipitates out of the water  

∙ Free oxygen in the air from cyanobacteria  

o Causes banded iron formations  

o 2 – 2.4 billion years ago