600 Million Years and Counting…
I was pretty bored so I decided to make some GIFs of the last 600 million years of our planet’s plate tectonics.
The first GIF is a global mollewide projection. The second one is of the Colorado Plateau and the North American Southwest. The next GIF is of the entire formation of the North American Continent. The fourth GIF is of geologic and tectonic evolution of Europe. And finally the last one is the same as the first except in rectangular format.
I obtained the images from Global Paleogeography and them compiled them one by one into Photoshop with the end result being the above GIFs.
These rock layers may not look that distinctive, but to geologists these tell a really cool story. These are turbidites, the remnants of debris flows off the shore of an ancient ocean.
Turbidites form when sediment piles up just off of a shoreline, often carried to the area by a river. Eventually, even underwater, big enough piles of sediment will collapse and avalanche downslope. Sometimes they do so under their own weight, sometimes an earthquake will set them off.
The avalanche of debris produces a recognizable pattern to geologists. The heaviest particles, the biggest grains, settle out at the bottom of the debris flow, and the sequence “fines upward”, meaning the grain sizes get smaller.
A typical turbidite will start at the bottom with sandy grains, maybe even larger stuff, and the grain size will decrease going upward as progressively finer grains settle out. Finally, each turbidite is topped by a layer of very fine grained clay particles that can even be a different color from the stuff below it. This sequence even has a name – the “Bouma” sequence.
Turbidites show up throughout the geologic record because they’re easily preserved. They form in areas in the ocean that aren’t likely to be eroded and they form in areas with lots of sediment that can bury and protect them afterwards. This sequence photographed here is about 10 separate turbidites; the whole outcrop probably has a lot more.
Image credit: Brian Romans (Creative commons):
Around Jenny Lake
Grand Teton National Park, Wyoming
(gneiss, quartz, granite, garnet, schist)
photo by rivermusic, June 2013
END-CRETACEOUS (65 Ma)
[Also formerly known as the Cretaceous-Tertiary (K-T) and now as the Cretaceous-Paleogene (K-Pg) extinction]
Severity: 5th worst
Cause: Meteorite impact released CO2 from carbonates
Climate: Cold (SO2) then warm (CO2)
Aftermath: Mammals arise
Even though the End-Cretaceous is the least severe of all the mass extinctions, with 62% of species and 11% of families wiped out, it’s probably the most well-known. (Say goodbye to our dinosaur friends!) The hardest hit animals included: dinosaurs (except Aves), pterosaurs, corals, echinoids, ammonites and belemnites, brachiopods, bivalve molluscs, and foraminifera.
Luckily for us, mammals were among those that fared better, along with turtles, lizards and snakes, birds, amphibians, and fish.
Most people are familiar with the theory that a meteorite impact was the cause of this mass extinction, but what really did happen and what can be proven?
Back in 1980 in Gubbio, Italy, father-son duo of Luis and Walter Alvarez measured an iridium abundance in the K-Pg boundary clay. Iridium is not a very common element in the Earth’s crust, so they knew it must have come from an extraterrestrial source. This observation would lead to inferring that there must have been a massive meteorite impact, but they would have to find the actual impact crater.
In the K-Pg boundary layer around the Caribbean, tektites, shocked quartz, and tsunami deposits were discovered, all of which would be indicative of a nearby meteorite impact.
The half-submerged Chicxulub crater was soon discovered in the Yucatan of Mexico, and impact glass yielded a 39Ar/40Ar age of 65 Ma, the exact age of the K-Pg boundary, making it the perfect candidate.
A large portion of this impact’s deadliness would have been due to the target rocks, which are mainly carbonates and evaporites. Upon impact, the rocks would have been vaporized, releasing large amounts of CO2 and SO2.
However, this mystery still isn’t fully solved. Around the same time, the Deccan Traps in India were effusively erupting, and as we saw in the End-Permain extinction, flood basalt events can produce absolutely disastrous effects.
We then have to ask ourselves: Was the impact really the only (or primary) cause of the extinction? What would have been the actual kill mechanism? And what was the role of the Deccan Traps?
Click HERE to see all Mass Extinction Monday posts
Azurite sea horse
We often return to the copper carbonate minerals such as azurite and malachite, since they form in such a wide diversity of habits and display such lovely and intense blues and greens. Sometimes nature turns up evocativepatterns of crystallisation such as the naturally formed sea horse shape of this crystal group, mined in the Sonora district of Mexico last November and measuring 17.4 x 8.5 x 3.0 cm. This crystal group is what is known as a floater, found freely floating in a pocket (usually filled with clays) rather than directly connected to the surrounding rock.
Copper deposits are often (but by no means always) formed from the juices spat out by freshly emplaced cooling granites that have concentrated within them all the elements that do not fit into the crystal structures of the common granitic minerals such as quartz, feldspar and mica. The granites are effectively acting as giant Earth stills, distilling metals out of the lower crust and mantle within their magma. Once the fluids have deposited their precious cargo in veins and small fractures within the infiltrated rocks, the results are often chemically altered by contact with mineralised groundwater, which oxidises the original minerals and transforms them into secondary minerals such as copper carbonate.
Image credit: Joe Budd/Rob Lavinsky/iRocks.com
Visited the Ben E. Clement Mineral Museum in Marion, Kentucky the other day and found a friend among the quartz!
The ultimate living fossil?
Yet again a museum drawer full of unclassified samples gave out a big surprise, when researchers got round to examining the specimens from a 1986 dredging expedition between 400 and 1000 metres down. Two recently discovered mushroom shaped organisms have defied attempts to classify them into any of the known phyla on life’s great bush, after their discovery in the seas off Australia. The research team think that they may be descended from the first known multicellular organisms to grow in the world’s seas some 600 million years ago, during the recently recognised Ediacaran era.
These fossil creatures have long intrigued researchers, and date from the great thaw after the Snowball Earth events (see http://tinyurl.com/okz5zlx). Assigning them to currently known phyla has proved tenuous at best, and many researchers have termed them a failed experiment that vanished completely, supplanted by the appearance of recognisable life forms and the radiation of ‘conventional’ organisms. They aren’t even sure what they consisted of, suggestions include fungi, microbial colonies and lichens.
Most of them disappeared during the Cambrian explosion after 542 million years ago, during which all the currently known phyla appeared. The latest known Ediacaran fossil found to date comes from around half a billion years ago. If these new organisms are indeed related to them, then their survival marks the longest lasting living fossils. They are formed of an outer skin and inner stomach separated by a layer of dense jelly. The new phylum has been named Dendrogramma .
The Ediacaran was officially recognised as an era in 2004 by the international commission on stratigraphy. It covers the period when the last snowball Earth glaciations of the proposed Cryogenian era ended (see our previous post at http://tinyurl.com/bvvysmj), involved an atmospheric oxidation event and saw the transition towards the Cambrian and its explosion of hard shelled organisms. Palaeontologically, it was marked by the radiation of the first large complex multicellular organisms, which are still described by many scientists as ‘enigmatic’. These were discovered by Australian geolegend Reg Sprigg, and later found in widespread locations around the globe.
An attempt will now be made to find living specimens of the creatures.
Image credit: Plos One
Our past post on the Ediacaran biota:http://tinyurl.com/ma236fa
Original article, free access: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0102976
The Ediacaran: an intro: http://www.ucmp.berkeley.edu/vendian/ediacaran.php
END-TRIASSIC (200 Ma)
Severity: 4th worst
Cause: Central Atlantic Flood Basalts, meteorite impact (?)
Climate: Hot; Pangaea mostly desert
Aftermath: Dinosaurs diversify
Only 50 My after the End-Permian extinction, 65% of species and 12% of families were wiped out during the End-Triassic extinction.
The exact cause of this extinction is still not very well constrained. It could possibly be due to flood basalts again. While the Siberian Traps had certainly cooled down, the Central Atlantic Magmatic Province was highly active, as the supercontinent Pangaea was beginning to breakup.
A meteorite impact has also been offered as a possible cause. However, the Manicouagan crater in Québec that has been offered as the possible impact site is slightly too old to be a very likely candidate at around 206-214 Ma.
Click HERE to see all Mass Extinction Monday posts