Geology In

Giant Trilobite Fossil Found on Australia

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<tr><td class="tr-caption" style="text-align: center;">A specimen of Redlichia rex from the Emu Bay Shale, Kangaroo Island, Australia. Image credit: Holmes et al, An artist’s impression of Redlichia rex on the Cambrian seafloor. Image credit: Katrina Kenny.</td></tr>
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<span style="font-family: Georgia, "Times New Roman", serif;"> Paleontologists have unearthed fossils of a giant trilobite species that inhabited Australian waters approximately 500 million years ago (Cambrian period).</span></h4>
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<span style="font-family: "georgia" , "times new roman" , serif;">Fossils of a giant new species from the long-extinct group of sea creatures called trilobites have been found on Kangaroo Island, South Australia.</span></div>
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The finding is adding important insights to our knowledge of the Cambrian 'explosion', the greatest diversification event in the history of life on Earth, when almost all animal groups suddenly appeared over half-a-billion years ago.</div>
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Trilobites, which had hard, calcified, armour-like skeletons over their bodies, are related to modern crustaceans and insects. They are one of the most successful fossil animal groups, surviving for about 270 million years (521 to 252 million years ago). Because of their abundance in the fossil record, they are considered a model group for understanding this evolutionary period.</div>
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"We decided to name this new species of trilobite<i> Redlichia rex</i> (similar to <i>Tyrannosaurus rex</i>) because of its giant size, as well as its formidable legs with spines used for crushing and shredding food -- which may have been other trilobites," says James Holmes, PhD student with the University of Adelaide's School of Biological Sciences, who led the research.</div>
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The preservation of trilobite 'soft parts' such as the antennae and legs is extremely rare. The new species was discovered at the Emu Bay Shale on Kangaroo Island, a world-renowned deposit famous for this type of preservation. The findings have been published in the Journal of Systematic Palaeontology by a team of scientists from the University of Adelaide, South Australian Museum and the University of New England.</div>
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The new species is about 500 million years old, and is the largest Cambrian trilobite discovered in Australia. It grew to around 30 cm in length, which is almost twice the size of other Australian trilobites of similar age.</div>
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"Interestingly, trilobite specimens from the Emu Bay Shale -- including <i>Redlichia rex</i> -- exhibit injuries that were caused by shell-crushing predators," says senior study author Associate Professor Diego García-Bellido, from the University of Adelaide and the South Australian Museum.</div>
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"There are also large specimens of fossilised poo (or coprolites) containing trilobite fragments in this fossil deposit. The large size of injured <i>Redlichia rex</i> specimens and the associated coprolites suggests that either much bigger predators were targeting <i>Redlichia rex</i>, such as Anomalocaris -- an even larger shrimp-like creature -- or that the new species had cannibalistic tendencies."</div>
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One of the major drivers of the Cambrian explosion was likely an evolutionary "arms race" between predators and prey, with each developing more effective measures of defence (such as the evolution of shells) and attack.</div>
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"The overall size and crushing legs of <i>Redlichia rex</i> are a likely consequence of the arms race that occurred at this time" says James Holmes. "This giant trilobite was likely the terror of smaller creatures on the Cambrian seafloor."</div>
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Specimens of Redlichia rex and other Emu Bay Shale fossils are currently on display in the South Australian Museum.</div>
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="https://www.adelaide.edu.au/news/news107262.html" rel="nofollow" target="_blank">Materials</a> provided by <a href="https://www.adelaide.edu.au/" rel="nofollow" target="_blank">University of Adelaide</a>.</span></i></u></div>
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Giant Trilobite Fossil Found on Australia

A specimen of Redlichia rex from the Emu Bay Shale, Kangaroo Island, Australia. Image credit: Holmes et al, An artist’s impression of Red...

What is Fire Agate?

gemstones, Mineral, Mineralogy 7:02 PM

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<tr><td class="tr-caption" style="text-align: center;">Photo Credit: Glenn Dizon </td></tr>
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<span style="font-family: "georgia" , "times new roman" , serif;">Agate is a semi-precious gemstone formed by relatively recent volcanic activity. It is outwardly similar in appearance to quartz, but also shows interesting swirls, bubbles and patterns.</span><br />
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Fire agate, a variety of chalcedony, is a semi-precious natural gemstone discovered so far only in certain areas of central and northern Mexico and the southwestern United States (New Mexico, Arizona and California). <br />
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Fire agates have beautiful iridescent rainbow colors, similar to opal, with a measurement of hardness on the Mohs scale of between 5 and 7 which reduces the occurrence of scratching when polished gemstones are set in jewelry.<br />
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The vibrant iridescent rainbow colors found within fire agates, created by the Schiller effect as found in mother-of-pearl, is caused by the alternating silica and iron oxide layers which diffract and allow light to pass and form an interference of colors within the microstructure layering of the stone causing the fire effect for which it is named.<br />
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<tr><td class="tr-caption" style="text-align: center;">Photo: Isaac Jones</td></tr>
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<span style="font-family: "georgia" , "times new roman" , serif;">How Fire Agate and Chalcedony Form</span></h4>
The fire agate and chalcedony of the Southern New Mexico–Arizona border area is formed when low pressure and low temperature epithermal hydrothermal waters (50°-200°C / 122°-392°F) carrying colloidal SiO<sub>2</sub> and iron oxides are injected into cavities in volcanic rocks such as gas bubbles in flow rocks, irregular-shaped vug fillings, or along fault or bedding plane fractures.<br />
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Approximately 24-36 million years ago these areas were subjected to  massive volcanic activity during the Tertiary Period. The fire agates  were formed during this period of volcanism when hot water, saturated  with silica and iron oxide, repeatedly filled cracks and bubbles in the  surrounding rock.<br />
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<span style="color: blue;"><span style="font-family: "georgia" , "times new roman" , serif;">Fire Agate Gemstone Mineral Locations</span></span></h4>
<b><span style="font-family: "georgia" , "times new roman" , serif;">Deer Creek, Arizona</span></b><br />
Deer Creek Fire agate is well known for it's high quality fire agate gemstones and excellent lapidary rough. The fire agate from Deer Creek Arizona ranks high on the list of desired collected gemstones, mineral specimens, and lapidary gemstone cutting material. Located in the eastern foothills of the Galiuro Mountains southwest of Safford, Arizona, this area has several active fire agate mines. Some of the early pioneers in fire agate mining at Deer Creek were Larry Gray, Howard Imboden, Guy Paul and Cliff Willis.<br />
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<b><span style="font-family: "georgia" , "times new roman" , serif;">Cuesta Fire Agate Mine - Arizona</span></b><br />
<a href="http://cuestafireagatemine.ilandwyte.com/" rel="nofollow" target="_blank">Cuesta Fire Agate</a> mine is a Desert Dig. when you come out to the Mine, you go to the claims and you can dig to your hearts content. without restrictions to what or where you can Dig. The Mine is open 12 months of the year.  fee: $30.00 - $50.00 a day, Tool Rentals, $5.00 a day.<br />
Address:  old Route 66 4 miles north of Oatman, AZ.<br />
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<b><span style="font-family: "georgia" , "times new roman" , serif;">Slaughter Mountain - Arizona </span></b><br />
Known for it's high quality fire agate gemstones and with it's rough often having multiple layers of fire banding, <a href="http://www.slaughtermountainfireagate.com/?fbclid=IwAR1h4VQFkhthjNQ6SmblrxSntpGXDxpAN0jAS7gg0Hj7_Dbi5vBwIjoC0Uk" rel="nofollow" target="_blank">Slaughter Mountain Fire</a> Agate is well suited for gemstone carving purposes. The mine at Slaughter Mountain is known for producing high quality fire agate gemstones, with intense color variations from bright reds and oranges to intense greens, purples and blues.<br />
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<b><span style="font-family: "georgia" , "times new roman" , serif;">See also:</span></b><br />
<a href="https://www.geologyin.com/2019/04/what-is-grape-agate.html" target="_blank">What Is Grape Agate?</a><br />
<a href="https://www.geologyin.com/2018/04/tourmaline-species-and-color-varieties.html" target="_blank">Tourmaline: Species and Color Varieties</a><br />
<a href="https://www.geologyin.com/2018/03/types-of-iridescent-gemstones-minerals.html" target="_blank">Types of Iridescent Gemstones & Minerals </a></div>

What is Fire Agate?

Photo Credit: Glenn Dizon Agate is a semi-precious gemstone formed by relatively recent volcanic activity. It is outwardly similar in...

1.2 Billion-Year-Old Meteorite Crater Discovered in Scotland

Earth History, Meteorite 8:33 PM

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<tr><td class="tr-caption" style="text-align: center;">Reddish-colored rocks of the Stac Fada deposit. Image: University of Oxford</td></tr>
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The biggest ever recorded meteorite collision location has been discovered in the U.K. Scientists find 9 MILE wide crater in Scotland caused by the 'biggest meteorite collision in Britain's history' 1.2 billion years ago<br />
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Evidence for the ancient, 1.2 billion years old, meteorite strike, was first discovered in 2008 near Ullapool, NW Scotland by scientists from Oxford and Aberdeen Universities. The thickness and extent of the debris deposit they found suggested the impact crater -- made by a meteorite estimated at 1km wide -- was close to the coast, but its precise location remained a mystery.<br />
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In a paper published today in Journal of the Geological Society, a team led by Dr Ken Amor from the Department of Earth Sciences at Oxford University, show how they have identified the crater location 15-20km west of a remote part of the Scottish coastline. It is buried beneath both water and younger rocks in the Minch Basin.<br />
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Dr Ken Amor said: 'The material excavated during a giant meteorite impact is rarely preserved on Earth, because it is rapidly eroded, so this is a really exciting discovery. It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.<br />
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'The next step will be a detailed geophysical survey in our target area of the Minch Basin.'<br />
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Using a combination of field observations, the distribution of broken rock fragments known as basement clasts and the alignment of magnetic particles, the team was able to gauge the direction the meteorite material took at several locations, and plotted the likely source of the crater.<br />
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Dr Ken Amor said: 'It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area.'<br />
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1.2 billion years ago most of life on Earth was still in the oceans and there were no plants on the land. At that time Scotland would have been quite close to the equator and in a semi-arid environment. The landscape would have looked a bit like Mars when it had water at the surface.<br />
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Earth and other planets may have suffered a higher rate of meteorite impacts in the distant past, as they collided with debris left over from the formation of the early solar system.<br />
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However, there is a possibility that a similar event will happen in the future given the number of asteroid and comet fragments floating around in the solar system. Much smaller impacts, where the meteorite is only a few meters across are thought to be relatively common perhaps occurring about once every 25 years on average.<br />
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It is thought that collisions with an object about 1 km (as in this instance) across occur between once every 100,000 years to once every one million years -- but estimates vary.<br />
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One of the reasons for this is that our terrestrial record of large impacts is poorly known because craters are obliterated by erosion, burial and plate tectonics.<br />
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="http://www.ox.ac.uk/news/2019-06-10-site-biggest-ever-meteorite-collision-uk-discovered" rel="nofollow" target="_blank">Materials</a> provided by <a href="http://www.ox.ac.uk/" rel="nofollow" target="_blank">University of Oxford</a>.</span></i></u></div>

1.2 Billion-Year-Old Meteorite Crater Discovered in Scotland

Reddish-colored rocks of the Stac Fada deposit. Image: University of Oxford The biggest ever recorded meteorite collision locati...

What Jumpstarted Earth's Plate Tectonics?

Earth History, Geology, Tectonic 8:06 PM

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<tr><td class="tr-caption" style="text-align: center;">World Tectonic Plates and Their Movement -</td></tr>
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Earth's outer layer is composed of giant plates that grind together, sliding past or dipping beneath one another, giving rise to earthquakes and volcanoes. These plates also separate at undersea mountain ridges, where molten rock spreads from the centers of ocean basins.<br />
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But this was not always the case. Early in Earth's history, the planet was covered by a single shell dotted with volcanoes -- much like the surface of Venus today. As Earth cooled, this shell began to fold and crack, eventually creating Earth's system of plate tectonics.<br />
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According to new research, the transition to <a href="https://www.geologyin.com/2014/09/how-plate-tectonics-works.html" target="_blank">plate tectonics</a> started with the help of lubricating sediments, scraped by glaciers from the slopes of Earth's first continents. As these sediments collected along the world's young coastlines, they helped to accelerate the motion of newly formed subduction faults, where a thinner oceanic plate dips beneath a thicker continental plate.<br />
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The new study, published in the journal Nature, is the first to suggest a role for sediments in the emergence and evolution of global plate tectonics. Michael Brown, a professor of geology at the University of Maryland, co-authored the research paper with Stephan Sobolev, a professor of geodynamics at the GFZ German Research Centre for Geosciences in Potsdam.<br />
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The findings suggest that sediment lubrication controls the rate at which Earth's crust grinds and churns. Sobolev and Brown found that two major periods of worldwide glaciation, which resulted in massive deposits of glacier-scrubbed sediment, each likely caused a subsequent boost in the global rate of plate tectonics.<br />
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The most recent such episode followed the "snowball Earth" that ended sometime around 635 million years ago, resulting in Earth's modern plate tectonic system.<br />
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"Earth hasn't always had plate tectonics and it hasn't always progressed at the same pace," Brown said. "It's gone through at least two periods of acceleration. There's evidence to suggest that tectonics also slowed to a relative crawl for nearly a billion years. In each case, we found a connection with the relative abundance -- or scarcity -- of glacial sediments."<br />
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Just as a machine needs grease to keep its parts moving freely, plate tectonics operates more efficiently with lubrication. While it may be hard to confuse the gritty consistency of clay, silt, sand and gravel with a slippery grease, the effect is largely the same at the continental scale, in the ocean trenches where tectonic plates meet.<br />
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"The same dynamic exists when drilling Earth's crust. You have to use mud -- a very fine clay mixed with water or oil -- because water or oil alone won't work as well," Brown said. "The mud particles help reduce friction on the drill bit. Our results suggest that tectonic plates also need this type of lubrication to keep moving."<br />
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Previous research on the western coast of South America was the first to identify a relationship between sediment lubrication and friction along a subduction fault. Off the coast of northern Chile, a relative lack of sediment in the fault trench creates high friction as the oceanic Nazca plate dips beneath the continental South America plate. This friction helped to push the highest peaks of the central Andes Mountains skyward as the continental plate squashed and deformed.<br />
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In contrast, further south there is a higher sediment load in the trench, resulting in less friction. This caused less deformation of the continental plate and, consequently, created smaller mountain peaks. But these findings were limited to one geographic area.<br />
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For their study, Sobolev and Brown used a geodynamic model of plate tectonics to simulate the effect of sediment lubrication on the rate of subduction. To verify their hypothesis, they checked for correlations between known periods of widespread glaciation and previously published data that indicate the presence of continental sediment in the oceans and trenches. For this step, Sobolev and Brown relied on two primary lines of evidence: the chemical signature of the influence of continental sediments on the chemistry of the oceans and indicators of sediment contamination in subduction-related volcanoes, much like those that make up today's "ring of fire" around the Pacific Ocean.<br />
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According to Sobolev and Brown's analysis, plate tectonics likely emerged on Earth between 3 and 2.5 billion years ago, around the time when Earth's first continents began to form. This time frame also coincides with the planet's first continental glaciation.<br />
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A major boost in plate tectonics then occurred between 2.2 to 1.8 billion years ago, following another global ice age that scrubbed massive amounts of sediments into the fault trenches at the edges of the continents.<br />
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The next billion years, from 1.75 billion to 750 million years ago, saw a global reduction in the rate of plate tectonics. This stage of Earth's history was so sedate, comparatively speaking, that it earned the nickname "the boring billion" among geologists.<br />
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Later, following the global "snowball Earth" glaciation that ended roughly 635 million years ago, the largest surface erosion event in Earth's history may have scrubbed more than a vertical mile of thickness from the surface of the continents. According to Sobolev and Brown, when these sediments reached the oceans, they kick-started the modern phase of active plate tectonics.<br />
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="http://dx.doi.org/10.1038/s41586-019-1258-4" rel="nofollow" target="_blank">Materials </a>provided by <a href="https://www.umd.edu/" rel="nofollow" target="_blank">University of Maryland</a>.</span></i></u></div>

What Jumpstarted Earth's Plate Tectonics?

World Tectonic Plates and Their Movement - Earth's outer layer is composed of giant plates that grind together, sliding past or d...

Study Confirms Banded Iron Formations Originated From Oxidized Iron

Earth History, Geochemistry, Rocks 9:04 PM

Study Confirms Banded Iron Formations Originated From Oxidized Iron

2.1 billion year old rock showing banded iron formation. Photo: André Karwath A new study by University of Alberta scientists shows th...

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Magnetism Discovered in the Earth's Mantle

earth, Earth's magnetic field, Geology 6:15 PM

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<tr><td class="tr-caption" style="text-align: center;">The interior of the Earth and the experiment graphically illustrated. The blue dotted lines show the magnetic field surrounding the Earth. The researchers pressed and heated samples of the iron oxide hematite found in the Earth's mantle between two diamonds (right) to simulate the extreme conditions in the Earth's mantle. They observed that the iron oxide is magnetic under these conditions. Credit: Timofey Fedotenko</td></tr>
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The huge magnetic field which surrounds the Earth, protecting it from radiation and charged particles from space—and which many animals even use for orientation purposes—is changing constantly, which is why geoscientists keep it constantly under surveillance. </div>
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The old well-known sources of the Earth's magnetic field are the Earth's core—down to 6,000 kilometres deep down inside the Earth—and the Earth's crust: in other words, the ground we stand on. The Earth's mantle, on the other hand, stretching from 35 to 2,900 kilometres below the Earth's surface, has so far largely been regarded as "magnetically dead." An international team of researchers from Germany, France, Denmark and the U.S. has now demonstrated that a form of iron oxide, hematite, can retain its magnetic properties even deep down in the Earth's mantle. This occurs in relatively cold tectonic plates, called slabs, which are found especially beneath the western Pacific Ocean.<br />
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"This new knowledge about the Earth's mantle and the strongly magnetic region in the western Pacific could throw new light on any observations of the Earth's magnetic field," says mineral physicist and first author Dr. Ilya Kupenko from the University of Münster (Germany). The new findings could, for example, be relevant for any future observations of the magnetic anomalies on the Earth and on other planets such as Mars. This is because Mars has no longer a dynamo and thus no source enabling a strong magnetic field originating from the core to be built up such as that on Earth. It might, therefore, now be worth taking a more detailed look on its mantle. The study has been published in Nature.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Background and methods used</span></h4>
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Deep in the metallic core of the Earth, it is liquid iron alloy that triggers electrical flows. In the outermost crust of the Earth, rocks cause magnetic signal. In the deeper regions of the Earth's interior, however, it was believed that the rocks lose their magnetic properties due to the very high temperatures and pressures.<br />
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The researchers now took a closer look at the main potential sources for magnetism in the Earth's mantle: iron oxides, which have a high critical temperature—i.e. the temperature above which material is no longer magnetic. In the Earth's mantle, iron oxides occur in slabs that are buried from the Earth's crust further into the mantle, as a result of tectonic shifts, a process called subduction. They can reach a depth within the Earth's interior of between 410 and 660 kilometres—the so-called transition zone between the upper and the lower mantle of the Earth. Previously, however, no one had succeeded in measuring the magnetic properties of the iron oxides at the extreme conditions of pressure and temperature found in this region.<br />
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Now the scientists combined two methods. Using a so-called diamond anvil cell, they squeezed micrometric-sized samples of iron oxide hematite between two diamonds, and heated them with lasers to reach pressures of up to 90 gigapascal and temperatures of over 1,000 °C (1,300 K). The researchers combined this method with so-called Mössbauer spectroscopy to probe the magnetic state of the samples by means of synchrotron radiation. This part of the study was carried out at the ESRF synchrotron facility in Grenoble, France, and this made it possible to observe the changes of the magnetic order in iron oxide.<br />
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The surprising result was that the hematite remained magnetic up to a temperature of around 925 °C (1,200 K) – the temperature prevailing in the subducted slabs beneath the western part of Pacific Ocean at the Earth's transition zone depth. "As a result, we are able to demonstrate that the Earth's mantle is not nearly as magnetically 'dead' as has so far been assumed," says Prof. Carmen Sanchez-Valle from the Institute of Mineralogy at Münster University. "These findings might justify other conclusions relating to the Earth's entire magnetic field," she adds.</div>
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<span style="font-family: "georgia" , "times new roman" , serif;">Relevance for investigations of the Earth's magnetic field and the movement of the poles</span></h4>
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By using satellites and studying rocks, researchers observe the Earth's magnetic field, as well as the local and regional changes in magnetic strength. Background: The geomagnetic poles of the Earth—not to be confused with the geographic poles—are constantly moving. As a result of this movement they have actually changed positions with each other every 200,000 to 300,000 years in the recent history of the Earth. The last poles flip happened 780,000 years ago, and last decades scientists report acceleration in the movement of the Earth magnetic poles. Flip of magnetic poles would have profound effect on modern human civilisation. Factors which control movements and flip of the magnetic poles, as well as directions they follow during overturn are not understood yet.<br />
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One of the poles' routes observed during the flips runs over the western Pacific, corresponding very noticeably to the proposed electromagnetic sources in the Earth's mantle. The researchers are therefore considering the possibility that the magnetic fields observed in the Pacific with the aid of rock records do not represent the migration route of the poles measured on the Earth's surface, but originate from the hitherto unknown electromagnetic source of hematite-containing rocks in the Earth's mantle beneath the West Pacific.<br />
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"What we now know—that there are magnetically ordered materials down there in the Earth's mantle—should be taken into account in any future analysis of the Earth's magnetic field and of the movement of the poles," says co-author Prof. Leonid Dubrovinsky at the Bavarian Research Institute of Experimental Geochemistry and Geophysics at Bayreuth University.</div>
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="https://www.uni-muenster.de/news/view.php?cmdid=10326&lang=en" rel="nofollow" target="_blank">materials </a>provided by the  <a href="https://www.uni-muenster.de/en/" rel="nofollow" target="_blank">University of Münster.</a></span></i></u></div>
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