The Villarica volcano in southern Chile, one of South America’s most active volcanos, changes the earth’s surface by expelling molten lava from the earth’s interior.

For a long time, geology was considered an art and not a science, the reason being that geology was mainly a descriptive activity. It lacked any meaningful quantitative approach and did not have a unifying theory that would tie together the various geologic processes. This changed in the mid-1960s with the acceptance of the theory of plate tectonics as well as various quantitative techniques.

Professor Edgar J. MCullough, a retired member of the University of Arizona Department of Geosciences, will present the fourth of four lectures on the Evolution of the Earth in the Great Room of the Arizona Senior Academy, at 2:30 p.m. Thursday (Sept.7).

In the Sept. 21 session, McCullough will discuss geologic history. In that lecture, McCullough is expected to describe how geologists are able to talk about things that have happened in the past 4.6 billion years.  For example, how do we know when and where mountain building has taken place; where oceans have covered large portions of continental areas; why we have “missing” time.

Edgar J. McCullough

The energy for the constructive processes comes from the interior of the Earth. This energy is thought to owe its origin to the initial compaction of the Earth, meteorite impacts on the forming earth and/or decay of radioactive minerals over time. Chemical changes occur over time that result in the formation of rocks like granite and the development of continents. The processes include volcanism, earthquakes, deformation and mountain building.

McCullough began teaching at the UA in the 1960s later became head of the UA Geosciences Department and dean of the College of Science.

Written by Charles Prewitt, Academy Village Volunteer

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How Geology Helps Interpret Earth’s History: September 2017
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