Banded Iron Formations (by Ale*)
The Banded Iron Formations (BIFs) are a series of stratigraphic rock units deposited at different times in different environments. They contain higher-than-usual amounts of iron (Fe). These deposits are all Precambrian in age, and the ones in the image in particular are Archean (older than 2.5 billion years ago, that is 2,500,000,000 years). The current explanation for the abundance of Fe in these layers, albeit not totally accepted by the scientific community, is that Fe existed in solution in Archean ocean waters in its reduced form. Sudden increase in the amount of available oxygen, caused by the beginning of photosynthetic life in the form of stromatolite-building cyanobacteria, would have caused the reduced Fe to oxidize to hematite (and possibly magnetite). There is evidence in the fossil and rock records of an increase in atmospheric oxygen right after the last deposited BIFs. BIFs were never to form again. At the very beginning, before any BIFs were ever deposited, the most common form of Fe on Earth’s surface was pyrite. Pyrite today would not stand a chance of preservation in subaerial environment because of the abundance of oxygen in the atmosphere.
Fuente: Flickr / greenriver
Erosion Spider, by John Clemens.
Toward the bottom of the Grand Canyon in Arizona, USA, lies the Middle Cambrian Bright Angel Shale, a variably coloured sequence of relatively soft sedimentary rocks, here sculpted by erosion into a spider-like outcrop decorated with small green desert shrubs.
Taken on 8 April 2013. Winner in the EGU Photo Contest 2014.
A starburst or red tourmaline stands out against its white surroundings. Tourmaline is the name for a group of related minerals; red tourmaline also can be called rubellite. Semiprecious gemstones, tourmalines belong to a family of borosilicate minerals. They come in a range of colors from red to black and are found from Madagascar to Maine. (via National Geographic)
Fuente: National Geographic
Earth From Space: Tidal Island (by europeanspaceagency)
This image acquired on 3 May 2012 from the Pleiades satellite shows the island of Mont Saint Michel and its surrounding bay in northwest France. Mont Saint Michel was a tidal island, meaning that it was surrounded by water at high tide and only when the waters receded was it reachable by foot. In the late 1800s, the causeway was raised to make it accessible from the mainland at all times. In this image, we can clearly see where the water meets the mud flats, with multiple channels weaving through the mud.
For more information and a higher resolution of this image, please visit: http://www.esa.int/esaEO/SEM3MN2VW3H_index_0.html
Credits: CNES 2012/Astrium Services/Spot Image
Fuente: Flickr / europeanspaceagency
Purple Fluorite Cubes, Mapimi, Durango (by cobalt123)
Purple Fluorite Cubes, Mapimi, Durango - Cobalt blue cubes of fluorite crystals, purple that tends towards blue, from Mina Ojuela in Mapimi, Durango. Shot through the glass display case, the central crystal measures about 3/8” square.
Fuente: Flickr / cobalt