1.6 The Modern Theory and Practice of Geology
• Writings about gems, fossils, earthquakes, and volcanoes date back 2300 years to the ancient Greeks.
• Aristotle
o Most influential Greek philosopher.
o His explanations of the natural world were not based on keen observations and experiments, rather arbitrary pronouncements.
o Unfortunately his ideas were believed for many centuries.
o Catastrophism
o Strongly influenced explanations of the evolution of the earth in the 17th and 18th centuries.
o Held that the earth's landscape such as mountains and canyons were the result of great catastrophes rather than the products of long periods of geologic time.
• Birth of Modern Geology
o In the late 18th century.
o James Hutton, Scottish physician.
"Father of modern geology".
Wrote "Theory of the Earth".
Set forth the principal of Uniformitarianism which states that physical laws which operate today have operated in the past.
Argued that geologic processes operated over long periods of time.
Bolide impact is an exception.
o Charles Lyell, English geologist
Given most credit for advancing basic principles of modern geology.
Between 1830 and 1872 produced numerous editions of his classical book "Principles of Geology".
Acceptance of Uniformitarianism meant acceptance of a very long history for the earth.
1.7 Origin of the Our System of Planets
• Nebular hypothesis
o Rotating cloud of dust and gases (Hydrogen and Helium) begins to contract.
o Most of the material is gravitationally swept to the center = sun. Some material forms a flattened disk.
o Planets begin to accrete from the material in the flattened disk which is orbiting the sun, due to gravitational effects.
o In time, most of the material is swept into planets/moons or lost into space.
o Planetary separation
o Inner (rocky=terrestrial) planets are high density and small in size, the gases having been swept away by the solar wind.
o Outer (gas giant) planets are low density and large in size with a large gaseous component.
Formation of Earth's moon by impact with Mars sized body.