CH 2 - A Scientific Narrative2

CH 2 - A Scientific Narrative2 - CHAPTER 2 A SCIENTIFIC...

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CHAPTER 2 A SCIENTIFIC NARRATIVE 2.1 EARLY ATTEMPTS AT QUANTIFYING THE MOMENT OF CREATION Immanuel Kant (chemistry). .. How long has the Sun been burning? o Sun was necessary at time of creation = therefore sun has been burning for? o James Hutton (1785, father of geology) – Why has Hadrian’s wall not shown more erosion? o Should have shown more erosion in comparison to the Earth, therefore Earth has to be many millions of years old von Helmholtz (introducing physics) – The gravitational energy of the Sun could account for 20 million years! o Hits the ground and bounces back up o How long would it have taken the sun to leak heat and get to its current temperature? o There is enough energy in the sun to keep it at that temperature for about 20 million years Lord Kelvin (1897, geophysics and 1900, solar physics) – less than 100 million years o Measure amount of heat leaking out of the Earth John Joly (evaporation of river waters to salt water) at least 90-100 million years o Rivers steal salt out of mountain = travel to ocean = evaporate = rain o How long would it take for this cycle rate to get ocean to its current salt level? o Looked at the evaporation of river waters into salt water o Rivers are leeching salt out of the salt waters and then it evaporates and rain o He examined the rate at which this process would cause the oceans to become as salty as they are Charles Walcott (paleontology - fossils and the geological clock ) o By about 1910, it was recognized that the fossil record and sedimentation preceding the fossil record required at least 1.6 billion years
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o You could get everything properly ordered from today backwards o Examined the rate of sedimentation and how many years would be necessary to achieve the oldest fossils Modern Physics – the radioactive clock o Late 1800’s Radioactivity discovered = if we know enough about an object’s radioactivity we can date rocks o Early dating of uranite rocks to 1.65 billion years (1899) o By the 1950s, the oldest materials found on Earth were dated to more than 4.5 billion years. .. 2.1.1 GEOLOGICAL TIME The geological time-line orders the “history” written by fossils into the rocks of the Earth. Geologists have known that Earth is very, very old since the early 19 th century. Geological Time = record of ordering See Geological Clock Notes 2.1.2 MODERM PHYSCS + THE RADIOACTIVE CLOCK The discovery of radioactivity by Becquerel about 100 years ago provided science a “clock” with which the “age” of rocks could be measured . ...numbers in years could be assigned to events in the geological record. Radioactive Decay Start with a large number, N , of radioactive atoms. .. their nuclei would decay according to a simple law, here described as a differential equation: dN(t) = ln2 N(t) dt t 1/2 ln2 = 0.69314718 (fixed number) – sign = # atoms is decreasing t = time t 1/2 = half life of a nucleous (after this amount of time has lapsed ½ the
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This note was uploaded on 01/09/2010 for the course EPSC 200 taught by Professor Jensen during the Winter '08 term at McGill.

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CH 2 - A Scientific Narrative2 - CHAPTER 2 A SCIENTIFIC...

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