Theories of the Earth

• History of Cartography• The Problem of Longitude• Time Zones• Theories of the Formation of Land Forms– Vulcanists & Neptunists– Steno’s Laws– Uniformitarianism – Continental Drift and Plate Tectonics

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.

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

246-194 BCE, Alexandria

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.

Map of the World by Eratosthenes

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

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

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.

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

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

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

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.

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.

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

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 (Niels Stensen); 1638-1686; Denmark-Norway and northern Germany

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.

Buffon (1707-1788) France

Hooke (1635-1703); this is a cartoon; a portrait from life has not been found

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 generate 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

Charles Lyell, 1st Baronet• 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

1797-1875, Scotland (Britain)

Below: Frontpiece of Principles of Geology

The Young Earth• Lord Kelvin argued that

the thermodynamics of cooling would make 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)

Continental Drift of Alfred Lothar Wegener• 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

1880-1930, Germany

Arthur Holmes

• One of the few Anglophone geologists who supported the continental drift theory

• Proposed that the mantle had convection currents, which moved the continents

1890-1965; England

Harry Hammond HessCombined • Convection currents in the mantle (from Holmes)• Magnetic striping• Central Atlantic rift valleyInto a theory of Seafloor Spreading as the driving force for Plate Tectonics

1906-1969, USA

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

The Earth as a Heat Engine