The Earth Story

DINOSAUR EXTINCTION CAUSED BY COMET, NEW RESEARCH SUGGESTS

In recent history there has been a general consensus that between 65 and 66 million years ago an enormous asteroid made fall on planet Earth. After the asteroid’s initial impact, an enormous cloud of dust was sent up into the atmosphere, blocking out most sunlight and in turn killing most plant life and dinosaurs. The crash site, Chicxulub Crater, is located on the Yucatan Peninsula and covers an area of about 25,450 km2 (9,826 miles2). Despite some scientists who believe that the extinction was caused by ongoing volcanic eruptions in Deccan Traps in India, recent evidence has concluded that whatever caused the Chicxulub Crater also caused the wipeout of the dinosaurs.

All of this has held true until a recent study carried out by two Dartmouth University researchers which strongly suggests that the impact on the Yucatan Peninsula was caused by a comet, rather than an asteroid. Professor Jason Moore and Mukul Sharma of the Department of Earth Sciences took a different route than other scientists in executing their research. Since unusually high iridium traces in and nearby the Chicxulub Crater would suggest an impact by an asteroid, most scientists have agreed that that was the cause of the dinosaurs’ extinction. However Professor Moore and Sharma attributed these unusually high levels of iridium to incorrect documentation and natural occurrences such as preferential concentration on the ocean floor.

After dismissing a lot of the excess iridium that has been detected in and around the impact zone, the two professors’ findings were quite interesting. They observed the levels of osmium, another element that was delivered from the object’s impact. The resulting data suggests that the impact generated far less debris than previously anticipated. Their research also suggests that the impact was one of a much smaller object and at a much higher velocity. Such qualifications are met by comets.

The two professors’ research has had both positive and negative feedback from the public. If anything, it will gear some more research into other directions differing from the asteroid theory. In the process, we are bound to make new discoveries about the Chicxulub Crater and the great extinction of the dinosaurs.

--Pete D

Image Credit: Julian Baum / Science Photo Library http://www.sciencephoto.com/media/172395/enlarge

References: 1. http://www.sciencedaily.com/releases/2013/04/130404122409.htm 2. http://www.huffingtonpost.com/2013/03/23/asteroid-killed-dinosaurs-comet-extinction_n_2937296.html 3. http://news.bbc.co.uk/2/hi/science/nature/8550504.stm

Colla wood

Wood is often fossilised by replacement with silica, sometimes even precious opal, but the variant found in Turkey is often coloured a beautiful blue by copper laced waters infiltrating through the rock. While it is usually found cut into domed cabochon gems, I always prefer rough, and this wonderful 25cm specimen is no exception. Native copper, green malachite, blue azurite and a bit of turquoise have all made it into the mix, and the colour reveals beautifully the pattern of fractures in the rock through which the fluids spread before ditching their metallic cargo. The minerals present tell us that these waters were oxidised (see http://on.fb.me/1I4XWKt for an explanation of what this means) and carbonate rich (malachite and azurite), with a hint of extra phosphorous (turquoise). The grain and knots in the ancient tree make a beautiful backdrop to the later mineralisation, superimposed like the silica as a palimpsest of natural pattern on a long dead tree.

Loz

Image credit: LGF Foundation

The king of jaspers

Named after the then owner ranch where it was first found in 1947, the silica rich breccia (a rock that has been fragmented by geological forces) known as Morrisonite porcelain jasper is one of the prettier examples of the genre. Porcelain is a moniker used by lapidaries to describe a microcrystalline silica that takes on a fine polish resembling ceramic.

It occurs as seams and pockets in silica rich volcanic rocks called rhyolite tuffs, the remnants of hot ash flows during powerful explosive eruptions, mostly coloured by different valencies of iron (see http://on.fb.me/1I4XWKt for an explanation) contained in the mud particles incorporated in the silica. The patterns caused by the tectonic disruption of the rock and infiltration by different pulses of fluids with their varied colouring elements have left the stone one of the most variegated and beautiful chalcedonies ever found.

The mines have long been closed, but plenty of old material from the mine's active period is still circulating, but the site is in the high desert region on the Idaho/Oregon border in the Owyhee mountains, where many other pretty jaspers occur.

Similar material comes from other places, including Madagascar, Willow creek in Idaho and Mexico. We also shared some time ago another red jasper (a mixture of silica and iron oxide rich mud) known as Mary Ellen jasper that replaces a microbial mat formation known as a stromatolite (see http://on.fb.me/1OCAiuq)

Loz

Image credit: 1: Rare Rocks and Gems 2: Captain Tenneal http://bit.ly/1mLUIXX http://bit.ly/1Kuyoh7 https://thegemshop.com/pages/morrisonite-location http://bit.ly/1ostsz2 http://bit.ly/1SW8ztq More photos: http://bit.ly/1mLUDUe

Antarctic Meltwater and Ocean Interaction

As ice, water, and air interact at the edges of outlet glaciers and ice shelves in Western Antarctica, it provides implications to predict the future climate. However, due to the influence of strong ice-climate feedbacks, predicting the Antarctic ice sheets contribution to future sea level rise is a challenge. The only way around this problem is to disentangle these ‘feedbacks’ to minimize uncertainty in predicting how the oceans might change in the future.

As ice melts along the West Antarctic Ice Sheet, fresh water flowing off the ice sheet plays a key role in reducing the salinity and the density of the ocean’s surface water. This makes the layers of ocean more distinct with lower-density water sitting on top. On the bottom is a layer of dense cool water known as the Antarctic Bottom Water. There is not much of mixing in the areas close to the ice margins. Furthermore, models show that the generation of the dense-cold Antarctic Bottom Water has decreased by 25%-50% and the waters at depths from 400 to 700 meters are subject to rapid warming in the next 200 years.

This scenario implies that there will be a critical decrease in the salinity and increase in the temperature around the edges of the ice sheet. Models also show that areas such as the Amundsen Sea in West Antarctica are more vulnerable to an influx in freshwater. The Amundsen Sea is an area of rapid contemporary change in the West Antarctic Ice Sheet. Although impact of this phenomenon is greatest in the Southern Ocean, these effects extend across the Southern Hemisphere.

Image Credit: Michelle Maria, Pixabay http://bit.ly/1Kp8RWd

Source: http://bit.ly/1o4K1Rz http://bit.ly/1JXcC5u

Palaeoclimatic inferences from amber

Amber is the fossilised resin of trees, and has been prized amongst the palaeontological community for the excellent preservation of insects, plant life and other microfossils which would otherwise decay. It can also tell us a little bit about the climatic and environmental conditions which prevailed at the resin formed.

Fossil resins have the ability to preserve pristine stable isotopes, with the most important to palaeoenvironmental reconstruction being hydrogen, oxygen and carbon. By measuring these stable isotopes, palaeontologists can determine whether fossil resins are relatively enriched in deuterium (a stable isotope of hydrogen), Carbon 13 and Oxygen 18 compared to modern equivalents. Carbon 13 is taken in by plants in different proportions depending on the oxygen content of the atmosphere, the species of plant and its environment. The same goes for deuterium and oxygen. We can then compare the ratios of hydrogen, oxygen and carbon with those from living plants, modern equivalents, to better understand ancient ecosystems. Unfortunately, amber cannot be used as an estimate of palaeotemperature.

Amber can also be analysed using other types of spectroscopy, one of the most important being Fourier transform infrared (FTIR) spectroscopy. The absorption spectra appears as a series of peaks which corresponds to the type of bonds between different types of atoms. We can think of them as a kind of "fingerprint", by looking at peaks at different wavelengths, we can deduce something about the chemistry of the plant which produced them. The interpretation of FTIR absorption spectra allow us to determine two important things.

Firstly, the chemotaxonomic group of the amber. Chemotaxonomy is the classification of any organism, in this case the amber (derived from the plants which produced it), based on differences and similarities in their chemical composition. Secondly, scientists can determine which group of trees produced the resin. Such inferences have the potential to support the reconstruction of ancient forests by determining the palaeobotanical source of fossil resins.

The chemical analysis of amber remains in its infancy, however, when combined with other palaeontological studies, we can therefore make more precise palaeoenvironmental reconstructions. Specifically, analysing the size and distribution of trees (to estimate forest density and composition) and their type of preservation. Palynology, the study of plant pollen, spores and microscopic planktonic organisms is also very important. Within a handful of soil, there are thousands of spore and pollen grains, which can tell us which types of plants are present within the environment. Palaeontologists use everything available to them, in order to make a good interpretation.

AHP

References A past post on the subject: http://on.fb.me/1H4fL1Y http://bit.ly/1ONe3Va http://bit.ly/1HOF0oV http://bit.ly/1PK9VE0 http://go.nasa.gov/1PK9Y2z

Image credit: Jonathan Abbatt

Flint: A rock made of life.

Flint is one of the oldest materials used by man, shaped by knapping into an incredible variety of tools, used with iron pyrite as a fire lighter, or in early firearms. It is also found in many of England's old buildings, particularly Norman churches. The beginning of our long relationship with this rock is lost in the mists of time, but advanced tools date from at least 1.75 million years ago when our ancestor Homo Erectus roamed the land. Southern England's pebbly beaches are mostly flint, with their magical tinkling noise as the waves of a North Sea storm roll in, carrying their cargoes of driftwood and the odd lump of amber floated over from the Baltic.

In Europe it is usually found within, or weathered out of, the upper Cretaceous chalk formation (deposited between 60-95 million years ago). This chalk started life as a white calcareous ooze at the bottom of a warm, shallow sea. It consists of the excreta of shrimp that ate plankton with calcium carbonate shells (called coccolithophores), and is therefore a form of very fine grained limestone with some mud and volcanic ash mixed in. Our earlier story on Beach head (link below) shows the stunning chalk cliffs found on Britain's southern coastline.

Within the chalk lie many horizons (horizontal beds) of flint nodules. Chert, another name for flint, is a mosaic of micro-crystalline quartz (crystals too small to see) and opal (amorphous silica). It is usually coloured black by organic matter/clay or orangey-brown by iron rich minerals such as haematite, and the nodules often have a thick white coating. These horizons have been used for stratigraphic correlation since Strata Smith's first geological maps in the late 18th century, and they reflect periods of silica rich deposition in the original sediments.

In our recent post on mineral evolution (link below) we discussed the importance of life/rock interactions in the creation of new minerals, here we have a similar tale about the origin of a rock. Flint formed in the complex processes of diagenesis, which transformed the ooze into the soft chalk we see today. The silica came from plankton shells and bits of sponges called spicules in the ooze. These partly dissolved in the water and were precipitated around or replaced a nucleus, often a fossil or worm burrow. It's thought that the silica was first deposited as a gel (see our story on opal, linked below), as it is often found filling sea urchin shells, creating perfect internal moulds. Over time the crystallinity increased as the gel was dissolved and re-precipitated.

The action happened some distance below the surface, where the layer of ooze containing oxygen from sea water met the anoxic layer below. Here bacteria called methanogens were busy eating by stripping oxygen from carbonate and sulphate, extracting the energy for their chemosynthetic lifestyle (some of the methane ends up in clathrates, link to recent story below). Others are feeding by decaying the organic matter in the ooze. The effect of this activity is to create complex gradients in water chemistry and acidity that end up first concentrating and then precipitating the dissolved silica into nodules. These grow layer by layer over a long time until the conditions change as the sediments are gently baked and pressed into rock. Some scientists think the horizons correspond to radiolarian blooms linked to seasonal or other factors. Others suggest that they mark a pause in sedimentation, when sponges thrived on the sea floor. Flint formation is rarer in today's seas, which have been depleted in silica since the Eocene. The silica richness of Cretaceous seas came from the higher rate of hydrothermal activity in mid ocean spreading ridges as Pangaea broke up.

Flint is therefore made from life's remains, by the action of bacteria during the birth process of a rock. This energetic dance is good illustration of the Taoist concept of jijimuge, which means 'the interpenetration of all things'. We keep on discovering new layers to this concept as our understanding of Earth as a series of interconnected dynamic systems grows.

Loz

Image credit: Paul Frogatt

http://www.quartzpage.de/flint.html

http://www.stoneagetools.co.uk/what-is-flint.htm

http://www.westsussexgeology.co.uk/page2-09-4.html

A chapter on the upper Cretaceous rocks of the UK: http://jncc.defra.gov.uk/pdf/v23chap1.pdf http://www.guardian.co.uk/science/2011/aug/31/hand-axes-oldest-advanced-stone-tools

You can read our piece on Beachy Head, one of England's chalk cliffs at:

https://www.facebook.com/photo.php?fbid=423328307728219&set=a.352867368107647.80532.352857924775258&type=1

on mineral evolution at: https://www.facebook.com/photo.php?fbid=488752257852490&set=a.487707811290268.1073741830.352857924775258&type=1

about opal formation at: https://www.facebook.com/photo.php?fbid=474086139319102&set=a.487707811290268.1073741830.352857924775258&type=3&src=https%3A%2F%2Ffbcdn-sphotos-e-a.akamaihd.net%2Fhphotos-ak-ash4%2F485343_474086139319102_1136965089_n.jpg&size=480%2C333

methane clathrates at: https://www.facebook.com/photo.php?fbid=490062364388146&set=a.490062084388174.1073741836.352857924775258&type=1

One mineral blanketing another

A nice shiny covering of tiny white crystals of druzy quartz have grown on top of some intergrown crystals of purple fluorite. Both minerals were born from fluid rich magmas, the last remnants of cooling granites that distilled and concentrated the rare elements such as fluorine and the surplus silica that didn't fit into the more common granitic minerals. The piece measures 10.8 x 7.9 x 6.2 cm.

Loz

Image credit: Rob Lavinsky/iRocks.com

Mud, mud, glorious mud …

Volcanic eruptions frequently make it into the news and are major natural hazards, but a different type of volcano, also associated with tectonic activity, can be found across the globe. Mud volcanoes form when muds and fluids, under pressure at depth, squeeze up through faults or fractures and are extruded to the surface. Like their magmatic big cousins, mud volcanoes can form cone-shaped domes with a central vent, but the cones are typically a few metres high at most. The "eruptions" take the form of a bubbling mud pool at the vent. The vents emit volatiles as big burps, typically rich in methane, but they may also be rich in metals transported from the depths. The mud volcanoes shown here, in Wushanting in south west Taiwan, pose no immediate threat from their continuous eruptions, but they may be responsible for transport of arsenic and other heavy metals to the surface from deep sediments where the fluids originated.

~ SATR

Image: mud volcanoes at Wushanting, Kaohsiung County, Taiwan (credit: SATR) Links: http://link.springer.com/article/10.1007%2Fs12665-011-1391-3 http://www.taiwan.gov.tw/ct.asp?xItem=36895&CtNode=2209&mp=1006

Sunstone

A few days ago we featured the mineral Labradorite, a type of feldspar with an iridescent, color-changing sheen due to planes and occasionally included iron minerals within the crystal structure that reflect light (http://tmblr.co/Zyv2Js1rgq0PY). The same mineral can produce a completely different gem if instead there are tiny copper minerals included within the structure. That gem is the Oregon Sunstone.

These rocks come from only a couple mines, particularly in the state of Oregon where they were discovered in the 1980s. Samples from this mine vary from colorless through dark oranges and reds, with the occasional green sample particularly rare. Like the other samples of labradorite, these sunstones can change color depending on the angle between the light, the stone, and the eye.

The sunstone was declared the state gem of Oregon in 1987.

-JBB

Image credit: Jessa and Mark Anderson https://flic.kr/p/7biAuq

http://bit.ly/1gmV70g

References: http://bit.ly/1DD27AO http://www.minerals.net/gemstone/labradorite_gemstone.aspx http://bit.ly/1KXyj4y

Iron

If you came upon this rock in some random field (without the pen for scale obviously), would you think there was anything special about it? Looks like just about any other rock, right? A bit of pitting on the surface, a bit reddish, has been exposed to the elements and to water, but seems pretty ordinary.

Well, if you were to accidentally kick this rock instead of putting a pen next to it for scale, you might discover that it was a lot more massive than you thought. If you then polished a bit of the surface, you would be surprised to find that this rock is composed dominantly of iron metal.

This rock is an iron meteorite from the collection at BYU. When iron meteorites fall through the atmosphere, they partially melt and create a dark crust on the surface, often with “thumbprint-shaped” patterns called regmaglypts created as the heat and friction causes parts of the surface to ablate. If you look closely at even this weathered sample, you can get some hint of that pattern remaining even though the harsh, water-rich conditions of Earth’s surface have eaten away at it and started to turn it to rust.

Bonus points if this is the first time you’ve seen the word regmaglypts and you can pronounce it correctly while saying it 3 times quickly.

-JBB

Image credit: Andrew Silver/USGS public domain http://library.usgs.gov/photo/#/item/51db5066e4b02290dffa09f3

Read more: http://meteorites.wustl.edu/id/regmaglypts.htm http://bit.ly/1Iv1Gul

Gypsum tumulus in Germany

The great Jurassic limestone platform that covers much of Western Europe was born when the sea levels were higher due to the breakup of the supercontinent Pangaea. As new oceans opened at the nascent spreading ridges, entire ocean basins rose due to the buoyancy imparted by the heated roiling mantle below that was fuelling the supercontinental split. This meant in practice that much of the land was covered by sea as the water was pushed out of its basins in very slow motion, and these ubiquitous limestones and the younger Cretaceous chalk (as in the White Cliffs of Dover) are the most obvious remnants of this process.

As the seas receded during the last 65 million years paralleling the cooling and gradual sinking of the heated oceanic crust, land emerged, and the forces of erosion started to play their part. Rainwater, acidified by the CO2 in the atmosphere dissolves limestone into karst landscapes, replete with caves and their attendant speleothems (such as stalactites and stalagmites). Complex chemical interactions often occur, with minerals being repeatedly dissolved and precipitated, and climatic oscillations (such as ice age cycles) imprinting their records.

Where the limestone (made of calcium carbonate) contains a proportion of the evaporite mineral gypsum (hydrated calcium sulphate, which results from shallow supersaturated water evaporating, as in a salt pan), these interesting mounds can form. They are most common in semi arid environments (which limestone regions often are, as the rainfall all percolates into the extensive cave systems below). They result from the repeated combination of heating and cooling with drying and wetting during the sun's daily and yearly cycles. This causes the gypsum to change to its dehydrated cousin anhydrite and back.

In time, the overall volume of the gypsum expands, as its crystal structure disaggregates a bit and more water is retained in the structure. The gypsum layer then peels off the underlying sediment and rises, forming a hollow dome. This specimen was snapped in the Harz Mountains, where they were once thought to be the residences of dwarves and gnomes.

Loz

Image credit: Gerhard Schuster

http://bit.ly/1Hs9Gu3

Can you guess what this image is? It's tough. It is in fact a macro image of a the wing of a Chrysiridia rhipheus; a Madagascan sunset moth. How cool is that! This moth is considered one of the most impressive and appealing looking lepidopterans in the world- which is easy to see from this picture. The artist behind this image is actually a biochemist called Linden Gledhill. Using various levels of magnification and an automated macro focusing rail, Linden manages to capture the intricacy of insects’ wings, creating a multidimensional, glittering composition and sharing with the rest of us the sophisticated beauty of the natural world. And there's more... loads more! I recommend heading over to Linden's Flickr and checking out more gorgeous macro photography:http://bit.ly/1rGTNqE -Jean