The Earth Story

·      natgeo@RobertClarkphoto People may disagree but I think that this picture is a beautiful thing, not because of the photography or because it looks like a painting by a modern art master, but because of what it is, and how it relates to the earth and to the modern life that we all enjoy. What is it? It is a slice of rock from Canada, representing a span of 500,000 to 750,000 years, offers clues to what the world was like before, during, and after the meteor struck Earth. A. Before the impact (Cretaceous): The transition from pale mudstone to coal shows the climate shifting from dry to wet, perhaps stressing dinosaurs, other fauna, and flora. B. Impact (66 million years ago): No dinosaur fossils are found in or above this layer. Cracked quartz and rare metals such as iridium (scarce on Earth but plentiful in some meteorites) suggest a meteor strike. C. After the impact (Paleogene): Micro­fossils in coal indicate that forests collapsed and ferns took over. Before the impact on the bottom of the rock is revealing a change in climate, shifting from a dry to wet environment. The center section where you can see the earth colored thin line is the time of the asteroid impact 66 million years ago, and the top section is a layer of the ash that covered the planet which leads to the death of most dinosaurs and the rise of Mammals. Where does the name come from? The first segment of the Cenozoic Era, from 65 million years ago until the present, has historically been called the Tertiary Period. The abbreviation for the boundary between the Cretaceous and Tertiary periods is the K-T boundary, where K is the abbreviation for the German form of the word Cretaceous. Thank you to the @RoyalTyrrell Museum......for allowing me to photograph this specimen.  #Dinosaurs #mammals #astroid

Upheaval Dome

Located in Canyonlands National Park, Utah, Upheaval Dome is a must-visit for any hiking/geology enthusiast. A huge structure, roughly 5 kilometers (3 miles) in diameter and over 300 meters (roughly a 1000 feet) at its deepest, Upheaval Dome is an area of overturned and fractured rock that looks like a bullseye in the Earth. What caused this gigantic structure? That is a question many scientists have been asking for decades. Because Upheaval Dome is located on top of a massive salt layer, the Paradox Salt layer to be exact, experts proposed an idea, that the structure was created through this salt layer pushing upwards, squeezed up because of the weight of the overlying rock and the relatively low density of the salt, much like how squishing a jelly donut will cause the jelly filling to break through the top of the donut. The upwelling salt then spread like a pancake and weathered away. The mystery? There is no salt or salt residue present anywhere on the surface!

The other theory is that Upheaval Dome was created by a meteorite impact. This impact would have caused the uplift that we see today and could explain the ideal circular shape of the structure. There have been no meteorite fragments found anywhere around the structure, however, there is one piece of evidence that convinces many experts that Upheaval Dome was formed by a meteorite impact. This piece of evidence is a piece of shocked quartz that was found on the rim of the structure. Shocked quartz is only seen in very quick, violent geologic events, namely meteorite impacts.

Salt dome or meteorite crater, if you want to see Upheaval Dome up close and personal, there is a hiking path for any interested visitors. Decide for yourself which one you think it might be!

-AND

Image Credit: https://flic.kr/p/ciSjn7 -Photo by Doc Searls

Sources: http://bit.ly/2tC1Ddg https://go.nasa.gov/2u77Sqn http://bit.ly/2sJS6xK

Shocked

This researcher is using a petrographic microscope to examine a mineral grain recovered from the just-completed effort to core and sample the rim of the crater generated during the Chicxulub Impact on the shores of what is today the Yucatan Peninsula (https://tmblr.co/Zyv2Js237-vel). The monitor shows the grain being seen under the microscope and also adds a scalebar.

The projected image is a grain of very fine sand only a hundred or so micrometers across. You’re actually looking at a bit of a sand grain that was shocked during the impact that killed the dinosaurs and was recovered from that drill core.

When an asteroid impacts a planet, part of the energy of that impact is converted into a shock wave. That wave propagates outwards through everything, distorting the atomic structures of every mineral grain it travels through. As the wave passes, first atoms are squeezed together, then they move back apart after the wave releases.

Shock waves can do lots of damage as they pass through a mineral. Some minerals can take the stress, but others fracture and some even completely melt. The mineral quartz responds to shock by producing “planar deformation features” – basically specific planes in the mineral have been kinked or broken, creating features that can be seen under a microscope.

The pattern of lines defined by the dark dots running from the upper left to the lower right of this grain establishes that it is a bit of shocked quartz (https://t.co/1N6HchliLV), a relic of the Chicxulub impact. The initial coring of this site is now complete and 1300 meters of core through the ring of the crater have been collected. They will now be taken back to facilities in the US and Germany where they will be opened and characterized.

-JBB

Image credit: Max Alexander/B612/Asteroid Day/BBC http://www.bbc.com/news/science-environment-36377679

Reference: http://bit.ly/1Z0rliw

Shocked Quartz

This is a grain of quartz, one of the most common minerals on Earth, viewed under a microscope. The grain is sand-sized, about 0.13 mm across.

The color variation in the grain occurs because the grain is a bit round, it is thinner at the edges and so the edges interact less with light that travels through than happens at the thicker core of the grain. But that’s not the shocking part of this shot.Those lines are called “planar deformation features” or “pdfs” (we had that abbreviation before Adobe, I promise). They form when intense shock waves travel through a quartz grain and partially disrupt the mineral structure. In other words, PDFs in quartz indicate that the grain was exposed to a large impact.

This quartz grain was found in a drill core that traveled through the Chesapeake Bay impact crater. Finding features like these in quartz grains can be close to diagnostic for verifying that an impact took place in some area, even with buried or eroded craters.

-JBB

Image credit: USGS http://geology.er.usgs.gov/eespteam/crater/shockquartz.html

Read more: http://www.sciencedirect.com/science/article/pii/0012821X9190066Q

Swedish Lake is an Impact Crater

The origin of Hummeln Lake in southern Sweden has been debated for nearly 2 centuries. The rounded shape of the main body led Geologists to think it may be an extinct volcano. In the 1960s, a new proposal emerged that the lake could be an impact crater. Now scientists have proof that a meteorite did indeed create the structure, making it one of the oldest known small impact craters on Earth. The Hummeln structure within the lake is a depression over 160m (525ft) deep and 1.2km (.7 miles) wide, created by a meteorite approximately 100 to 150m (325 to 490ft) in diameter. This is small for an impact crater that is hundreds of millions of years old; typically craters of this size erode away, but this one was preserved by marine environments and sedimentation.

Scientists determined the origin by sampling the breccia around the lake. Breccia is a sedimentary rock composed of angular fragments of other rocks which are cemented together by smaller particles. This type of rock is not unusual, but the quartz grains (pictured) they found within them are very rare. The quartz displayed shock metamorphic features unique to hypervelocity impacts, confirming that Hummeln is an impact crater. It is the 187th confirmed meteorite impact crater on Earth.

Researchers used fossils to help determine that Hummeln is about 467 million years old. This is the same age as other nearby impact craters, including the Granby impact structure - a 2km (1.2 miles) wide crater about 150km (93 miles) away. This timeframe also aligns with a theorized meteor bombardment of Earth during the Late Ordovician period.

Scientists think two asteroids collided around 470 million years ago, resulting in a large number of impactors hitting Earth. Hummeln and Granby would have specifically come from pieces of asteroidal L-chondrite, which is thought to have broken up into smaller fragments that struck a number of places on Earth, including Sweden. The confirmation that Hummeln is an impact crater adds more evidence to support the theory of a Late Ordovician meteorite bombardment.

Photo Credit: Ludovic Ferrière, NHM Vienna

References: http://www.hou.usra.edu/meetings/lpsc2015/pdf/1758.pdf https://journals.uair.arizona.edu/index.php/maps/article/view/15382 http://www.livescience.com/49943-hummeln-impact-confirmed.html http://bit.ly/1DGoDTd