This presentation begins with a history of plate tectonics, also known as continental drift. Before the Second World War, belief in continental drift was largely limited to geologists who worked in the Southern Hemisphere. The availability of surplus magnetometers after the war changed that by producing a large volume of supporting evidence and by 1970 the theory was widely accepted. After that, the components of plate tectonic theory will be summarized, including the three types of boundaries, the thickness of the moving plates and deeper features known as hot spots. The last part of the presentation focuses on ongoing research topics; what happens to downgoing slabs, the driving mechanism of Atlantic opening and plate tectonic cycles earlier in Earth history.

Greg Croft is an independent petroleum consultant and a lecturer in Environmental and Earth Science at Saint Mary’s College in Moraga, California. He holds a PhD in Civil and Environmental Engineering from UC Berkeley, an MS in geophysics from Stanford and a BA in geology from UC Santa Barbara. Dr. Croft has more than 30 years’ experience in oil and gas exploration and production and is a frequent public speaker on energy issues and geology.

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We are a community-based network of people over age 50 who are united by our desire to remain in our own homes as we get older.


Ashby Village launched in 2010 after many discussions and community meetings that began in 2007. We are residents of Berkeley, Albany, Kensington, El Cerrito, Richmond and Oakland who are united by our desire to remain in our own homes as we get older. Because we know that we may increasingly need assistance and support as we age we pool resources by paying membership dues and volunteering our skills and time to support the Village infrastructure and to assist one another.

For more info please visit www.ashbyvillage.org or email us at info@ashbyvillage.org