GEO 101 Lecture Notes - Lecture 1: Continental Crust, Uniformitarianism
23 Jun 2018
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The Earth's Exterior
Various external forces affect the earth's surface, such as different climates and the
amount of rainfall. Freezing, thawing, and running water all contribute to weathering
and erosion, processes that break rock down into tiny particles. These particles are
then transported by water, ice, or wind as sediment. The processes of erosion reduce
mountains to hills, create canyons, valleys, and soils, and deposit huge amounts of
sediments that either become eroded again or are preserved and lithified into
sedimentary rock.
Geologic Time
Geoscientists have estimated the earth to be about 4.5 billion years old. As the crust
cooled, early geologic processes were largely volcanic, building up continental crust and
a primitive atmosphere. Bacterial forms of life have been found in rocks that are billions
of years old. Complex oceanic organisms such as trilobites began to appear only about
600 million years ago. From about 66 million to 245 million years ago, dinosaurs and
other reptiles flourished all over the world. In contrast, human beings have existed in
only about the last 3 million years, less than a thousandth of the age of Earth.
The Earth Today
Even though it is nearly 5 billion years old, the earth is still active, and landscapes are
constantly changing. The majority of continental rocks have been explored, studied, or
sampled. The principle of uniformitarianism—also known as “the present is the key to
the past”— is still applicable. Ancient rocks show textures that can be seen forming
today from processes such as volcanic eruptions, earthquakes, hot springs, wind,
weathering, river action, sedimentation, and erosion.
Technology now allows scientists to probe far deeper than Hutton or Lyell could
centuries ago. Underwater cameras, microscopes, geophysical equipment, analytical
techniques, sensing devices, and drilling advancements have allowed us to better
determine how rocks form. Scientists use uniformitarianism to apply this knowledge to
older rocks to better understand the complex history of the earth.
History of Physical Geology
Physical geology is the study of the earth's rocks, minerals, and soils and how they
have formed through time. Complex internal processes such as plate tectonics and
mountain building have formed these rocks and brought them to the earth's surface. ‐
Earthquakes are the result of the sudden movement of crustal plates, releasing internal
energy that becomes destructive at the surface. Internal heat and energy are released
also through volcanic eruptions. External processes such as glaciation, running water,
weathering, and erosion have formed the landscapes we see today.
About 2300 years ago, the Greeks, led by the philosopher Aristotle, were among the
first to try to understand the earth. During the 1600s and 1700s, scientists believed the
find more resources at oneclass.com
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Document Summary
Various external forces affect the earth"s surface, such as different climates and the amount of rainfall. Freezing, thawing, and running water all contribute to weathering and erosion, processes that break rock down into tiny particles. These particles are then transported by water, ice, or wind as sediment. The processes of erosion reduce mountains to hills, create canyons, valleys, and soils, and deposit huge amounts of sediments that either become eroded again or are preserved and lithified into sedimentary rock. Geoscientists have estimated the earth to be about 4. 5 billion years old. As the crust cooled, early geologic processes were largely volcanic, building up continental crust and a primitive atmosphere. Bacterial forms of life have been found in rocks that are billions of years old. Complex oceanic organisms such as trilobites began to appear only about. From about 66 million to 245 million years ago, dinosaurs and other reptiles flourished all over the world.
