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Arches National Park Geology Tour provides an extensive, visually rich description of the geology of Arches, by Deborah Ragland, Ph.D. See our DVD collection.
Here's a scuba diver making friends with a fish!
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Courtesy of Corel Photography

Open-Circuit Scuba

Scuba stands for self-contained, underwater breathing apparatus. It means that scuba divers carry all of the breathing medium they need with them for the duration they are underwater. Open-Circuit scuba is different than Closed-Circuit scuba and Semi-Closed Circuit scuba.

In Closed-Circuit scuba there is a total recirculation of the gas supplied to the diver. In Semi-Closed Circuit scuba, some of the gas is reused by the diver. In contrast, the gas supplied during Open-Circuit scuba is not recycled at all. When a diver breathes out, the exhalation goes out to the surrounding water instead of being recirculated somehow.

In Closed-Circuit scuba, oxygen and mixed gas are used as the gas supply for the diver. In Semi-Closed Circuit scuba, mixed gas is used as the gas supply. In contrast, Open-Circuit scuba uses mixed gas and air as the gas supplies, with air being the main gas supply for Open-Circuit scuba divers.

There are risks involved in all kinds of scuba diving. Adequate training, experience, the presence of a dive buddy, and observation of dive tables should minimize the risks so that Open-Circuit can be a safe and enjoyable experience.


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The Spring 2010 issue of The Earth Scientist, focuses on the ocean, including articles on polar research, coral reefs, ocean acidification, and climate. Includes a gorgeous full color poster!

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA