From yalegeotravels (emphasis mine):
The first stop in Vredefort was of a basement granite exposure that contained thin veins of pseudotacylite stretching through it like spider webs. This black silicate infill was presumably once glass, which as a amorphous solid degrades readily over geologic time. At this outcrop, the veins were meters thick and contained large pieces of the host granite within them. This site was a decommissioned granite quarry where huge blocks of granite had been cut and harvested before it became uneconomical to do so.
The rounded edges of those granite chunks within the pseudotacylite matrix, many larger than a human head, showed the immediate heat that grasped them and the sheer fury of the upheaval from an asteroid impact. It takes a lot to liquify granite and feldspar, push the molten mixture through fractures in the host rock, and create enough pressure to propagate the veins throughout the host rock.
On that day some 2.02 billion years ago, you didn’t want to be at Vredefort.
It would have been a very bad day.
Stromatolites (by mrfuller)
These are the oldest lifeforms on Earth, existing for over 3.5 billion years. This is a UNESCO heritage site and one of the only places in the world to find living stromatolites. And they don’t mind the heat: It was 47˚C when I took this.
Fuente: Flickr / mrfuller
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