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Theories of the Earth

Theories of the Earth. The Earth is a Sphere. Known to the ancients and assumed by 500 BCE. Pythagoras assumed it was a sphere because it was the perfect shape. Aristotle argu ed that it was a sphere in De Caelo :

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Theories of the Earth

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  1. Theories of the Earth

  2. The Earth is a Sphere • Known to the ancients and assumed by 500 BCE. • Pythagoras assumed it was a sphere because it was the perfect shape. • Aristotle argued that it was a sphere in De Caelo: • Every portion of the Earth tends toward the center until by compression and convergence they form a sphere. • Travelers going south see southern constellations rise higher above the horizon. • The shadow of Earth on the Moon during a lunar eclipse is round.

  3. Eratosthenes of Cyrene • Believed that the sun was the center and very far away • Calculated the circumference of the earth, which was within 0.2% of current measurements • Assumptions: • That Alexandria and Syene lie on the same meridian. • That the distance between Alexandria and Syene is 5000 stades. • That the Earth is a sphere. 246-194 BCE, Alexandria

  4. Map of the World by Eratosthenes

  5. Claudius Ptolemaeus • Wrote one of the most influential geographical atlases (called Geographica) • He used a coordinate system with the prime meridian near the Azores. 90-168; Alexandria Ptolemy’s world map published in Geographica

  6. Gerardus Mercator (Gerard de Kremer) • Challenge to convert a sphere to a flat surface • Mercator projected the spherical earth to a cylinder with a coordinate system which kept angles (courses) constant but varied distance. 1512-1594; Belgium and Germany

  7. Cassini Family and the Mapping of France Careful surface measurements and triangulation Giovanni Domenico Cassini (1625-1712); Italy and France was the first. The atlas of France was finally published by Caesar-Francois Cassini (1714-1784) and continued by the Cassini family until 1815.

  8. The Longitude Prize • The method of determining Latitude relies only on making careful measurements of a position relative to the sun or the North Star • Longitude is very different and ships out of sight of land had to rely on dead reckoning. • The British government offered a monetary prize for a simple and reliable way to determine Longitude by act of Parliament 1714

  9. Proposed Solutions • Galileo (1612) had proposed (long before) to use the moons of Jupiter • Halley (1683) had proposed to use the position of the moon against the fixed stars • Tobias Mayer proposed using the distance to the moon • John Harrison proposed using clocks set at the time of a known longitude and compare that with the local solar time to determine local longitude

  10. The Chronometry Method • John Harrison had to make a new type of clock that would not stop when a ship tosses and rolls • He also had to make a clock that was very reliable. • His clocks or chronometers were designated H1-H4. • H4 performed perfectly in trials of 1761 according to the rules, but not awarded the prize. • Outperformed the lunar method on the second trial and still no award • King George heard of the problem and demanded the Longitude Board award the prize to Harrison and threatened to appear in parliament • Awarded a partial sum in 1773 • The full prize was never awarded to anyone H4, the winner 1693-1776, Britain

  11. The Prime Meridian The Prime Meridian at Greenwich Observatory adopted for British Ordinance mapping survey in 1851. Gradually adopted as the Prime Meridian all over the world in 1884. The current GPS reference meridian is about 102m east of the 1851 line.

  12. Time Zones • The earth turns about 15 degrees per hour. • Local solar time became dangerous with the advent of the railroad. • Time zones established at the Railway General Time Convention of 1883 and adopted by the US Congress by the Standard Time Act of 1918 • GMT is mean solar time at Greenwich Observatory. • UTC (universal time) is based on an atomic clock that takes into account leap seconds.

  13. Rival Theories of the Earth • Neptunists: the geology of the earth could be accounted for by the action of water alone, and by processes that no longer operate. They also tended to be catastrophists (referencing the Noachian Flood). Founded by Abraham Werner • Vulcanists (Plutonists): the geology of the earth can be explained by gradual volcanic activity and erosion. View founded by Abbe Anton Moro (1687-1764), Italy. Abraham Gottlob Werner (1749-1817), Present-day Poland

  14. Steno’s Laws • Rock layers are laid down in an aqueous medium • The Law of Horizontality • The Law of Superposition • Departure from horizontal is a result of alteration by earthquakes or volcanoes • Published in 1668 as Prodromus Nicolas Steno (NielsStensen); 1638-1686; Denmark-Norway and northern Germany

  15. Hooke and Buffon • Robert Hooke (1635-1703) Ireland and England interpreted the rocks of the Isle of Wight as having been laid down over a long period of time through repeated catastrophes. • George-Louis Leclerc, Comte de Buffon (1707-1788) noted that the earth must be much older than the 6,000 years interpreted from Genesis. Speculated it could be as old as 75,000 years. Hooke (1635-1703); this is a cartoon; a portrait from life has not been found Buffon (1707-1788) France

  16. James Hutton • Became Plutonist and advocated Uniformatarian Principle • We find no vestige of a beginning, no prospect of an end (1795). • The earth goes through cycles which generates soil • Looked for unconformities Rock on left slopes to the sea and lies on top of much older rock that slopes to the right. 1726-1797, Scotland

  17. Charles Lyell, 1st Baronet 1797-1875, Scotlant (Britain) Below: Frontpiece of Principles of Geology • Strong advocate for the Huttonian Geology with uniformitarianism as its centerpiece • Wrote Principles of Geology • One of the most influential scientists of the 19th century and confidant of Charles Darwin

  18. The Young Earth • Lord Kelvin argued that the thermodynamics of cooling would mmake the earth no older than 100 million years if it started as a molten ball • Lyell’s Geology required much more time • Time problem resolved with the discovery of radioactivity William Thomson, 1st Baron Kelvin, 1824-1907, Ireland (UK)

  19. Continental Drift of AlfredLotharWegener 1880-1930, Germany • Meteorologist and polar explorer • Study of maps led him to suppose that the continents had once been joined • Broke apart by ‘pole-fleeing force’ and tidal forces with the sun

  20. Harry Hammond Hess • Convection currents in the mantle • Seafloor spreading 1906-1969, USA

  21. Basalt and Granite • Basalt is fine-grained and high in iron and magnesium and has a density of 2.8-3.0g/ml • Granite is coarse-grained and high in silicates with a density of 2.6-2.7g/ml Basalt-like diabase intrusion into granite at Schoodic Point in Maine

  22. The Earth as a Heat Engine

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