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CalciumLast Updated on 2013-10-24 16:29:12Calcium is the chemical element with atomic number 20; it has an atomic mass of 40.078 atomic mass units (amu). The chemical symbol for calcium is Ca. Calcium is a soft gray alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust; moreover, it is the fifth most abundant dissolved ion in seawater both in terms of number of atoms and mass, after sodium, chloride, magnesium, and sulfate.
Calcium an is essential nutrient for almost all living organisms, with vital roles in cellular metabolism, especially with regard to movement of the calcium ion Ca++ into and out of the cytoplasm functions as a signal for many cellular processes. As a chief component needed in mineralization of bones and shells, calcium is the most abundant metal by mass in a large number of faunal species, especially vertebrates, testudines and mollusca.
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Fate and effects of perchlorateLast Updated on 2013-09-17 22:20:28This article is the result of a collaborative effort between a student at Mount Holyoke College participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project, and an expert on the topic. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. This article has been reviewed by EoE editors.
Perchlorates are both man-made and naturally-occurring salts. Five types of this chemical are manufactured or mined in the United States (U.S.) and in other countries—ammonium perchlorate being the most common. Perchlorates exist in the environment as solids and they separate into two ions in water. The negatively charged anion is measured when water or other liquids are tested for perchlorates.
Perchlorate modulates thyroid function as a competitive... More »
AnthropoceneLast Updated on 2013-09-03 12:23:40
The Anthropocene defines Earth's most recent geologic time period as being human-influenced, or anthropogenic, based on overwhelming global evidence that atmospheric, geologic, hydrologic, biospheric and other earth system processes are now altered by humans. The word combines the root "anthropo", meaning "human" with the root "-cene", the standard suffix for "epoch" in geologic time. The Anthropocene is distinguished as a new period either after or within the Holocene, the current epoch, which began approximately 10,000 years ago (about 8000 BC) with the end of the last glacial period.
Anthropocene is a new term, proposed in 2000 by Nobel Prize winning scientist Paul Crutzen. A similar term, Anthrocene, was coined by Andrew Revkin in his 1992 book Global Warming: Understanding the Forecast, but was not adopted by scientists.... More »
Ocean Biogeographic Information System USALast Updated on 2012-08-05 00:00:00
Ocean Biogeographic Information System USA
Lead Image: A map of the world’s ocean showing target areas for biogeography of chemosynthetic ecosystems research. Area "A" (in pink) includes the Equatorial Atlantic Belt region, extending from the seeps off Costa Rica, through the Gulf of Mexico and Caribbean, and across the Atlantic to western Africa. Image courtesy of the ChEss Programme.
The Ocean Biogeographic Information System USA (OBIS-USA), a program of the United States Geological Survey (USGS) Core Science Analytics and Synthesis (CSAS), is the US national node of the Ocean Biogeographic Information System (OBIS). Meant to serve research and natural resource management needs, OBIS-USA brings together marine biological occurrence data in a standard format, with metadata, web-based discovery and download, and web service access for... More »
Zambezi RiverLast Updated on 2012-03-20 00:00:00
The Zambezi River, Africa's fourth largest after the Nile, Zaire and Niger rivers, exhibits a length of 2700 kilometers prior to discharge to the Indian Ocean in Mozambique.
Zambezi River with Zambia in foreground and Zimbabwe in background. @ C.Michael Hogan
Zambezi River at the junction of Namibia, Zambia, Zimbabwe and Botswana. Source: Brian McMorrow
From headwaters in northwest Zambia, the river flows:
southeast through a portion of eastern Angola;
south through western Zambia;
east along the Zambia-Namibia (Caprivi Strip) border to the junction of Namibia, Zambia, Zimbabwe and Botswana;
east along the border between Zambia and Zimbabwe over the dramatic Victoria Falls and on to Lake Kariba
east into Mozambique and Lake Cahora Bassa
south west... More »
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