Literally dig deeper into the earth surface and discover what is lying right under your feet.
Courtesy Mark RyanI recently attended a geology seminar sponsored by the Geological Society of Minnesota. The event took place at Macalester College in St. Paul, and was led by Jeff Thole, laboratory supervisor and instructor in the college's Geology Department. Jeff is extremely knowledgeable and enthusiastic about geology, and in the course of cramming a semester's worth of geology into the two hour lab, he mentioned that he had in his office one of the oldest rocks in the world: a nice chunk of Acasta gneiss. After finishing his talk about the rock cycle, and as everyone began examining the variety of rock types spread out on lab tables in several rooms, Jeff brought out the chunk of ancient gneiss for everyone to see.
Found on an island in the extreme and very isolated northern regions of Canada's Northwest Territories, the Acasta gneiss has been radiometrically dated to be upwards to 4.03 billion years old! That's a number that's not very easy to comprehend. The Earth itself is estimated to be just a half-billion years older, so the Acasta gneiss (pronounced nice) is some of the very earliest crustal rock still existing on Earth's ever-changing surface. For a rock unit to withstand 4 billion years of the rock cycle - where the forces of erosion and plate tectonics are constantly at work wearing down, reworking and remelting rocks - that's quite a feat if you think about it.
To give you a better idea of the vast amount of time we're talking about here, let's first reduce it to a more comprehendible time-frame. If you were able to take a single photograph of the Earth each year for those 4 billion years (4,000,000,000 photos) and then made a time-lapse video of all those photos (at 30 frames/photos per second), and started watching the video today, it would take you more than 4 years of constant, around-the-clock viewing to watch it from start to finish. You'd still be watching it in 2017, when non-avian dinosaurs suddenly go extinct about three-and-a-half weeks before the end of the video. We modern humans wouldn't appear for the first time until sometime in the show's last couple hours.
Courtesy D-Maps.comBut back to the rock itself. The ancient gneiss is named after the Acasta River, located east of Great Bear Lake, where the outcrop was first found in the 1980s. The exposure is about 300 kilometers (180 miles) from Yellowknife, so the only practical way to get there is by float plane.
Composed mostly of the minerals quartz and feldspar, the Acasta gneiss was formed during the Hadean, the earliest eon in Earth's history. Its composition leads geologists to surmise that it was probably formed from highly metamorphosed granite subjected to unimaginable heat and pressure. The exact origin of that granite is unknown, but its presence indicates continental crust (and surface water) were probably already present in those very ancient times.
AGE BEFORE BEAUTY
Courtesy Mark RyanIt may interest you to know that Minnesota has its own ancient gneisses exposed in outcrops in the Minnesota River Valley. The most well-known is the gneiss that's quarried around the town of Morton, Minnesota. At nearly 3.6 billion years old, Morton gneiss is not quite as ancient as the Acasta rock but what it lacks in age it makes up for in beauty. Known in the construction trade as Rainbow Granite, polished panels of the banded and severely swirled Archean-aged-aged migmatitic gneiss can be found decorating building facades throughout the country.
TECTONIC VS MARKET FORCES
An enterprising miner from Yellowknife has filed a claim on the Acasta gneiss site, and has been trying to market the ancient rock. This doesn't set well with many in the geological community, who think the rare outcrop should be preserved for scientific study. They also say the prospector could be misrepresenting the public since not all the rock in the exposure dates back to 4 billion years, and it's very expensive to validate the age of any one piece.
THE DATING GAME
So how exactly has the Acasta gneiss been dated so precisely? Zircon crystals found in the rock's mineral structure trap uranium in their lattices when they form and can act as timekeepers through measuring the decay of the uranium into lead. The half-life of uranium is a known number (4.47 billion years for U-238; 704 million years for U-235), so measuring the ratio between number of parent atoms (uranium) to the number of daughter atoms (lead) allows for a very precise estimation of age. But even zircon crystals aren't immune from 4 billion years of exposure to the elements. Things like naturally occurring radiation can damage or alter them and thus skew the measurements. But by using an instrument called the Sensitive High-Resolution Ion Microprobe (aka SHRIMP) researchers are able to focus a beam of oxygen ions on a tiny unaffected segment of the zircon' s surface, remove atoms from it, and then analyze their isotopic composition. The SHRIMP was developed at Australian National University.
Jeff Thole's sample was given to him by a geologist from the Geological Survey of Canada, which purchased a SHRIMP and used it to date the Acasta rocks. It should be noted that an older Canadian rock unit supposedly exists in the greenstone belt east of Hudson Bay, but there's still some contention regarding this, since the method of radiometric dating isn't the same that was used to date Acasta samples.
Whether the Acasta gneiss is the remaining crust of a protocontinent that existed when the Earth was still a relatively young, hot mass of accreted material remains a mystery at this point, but scientist named the time the Hadean for good reason: back then it must have been literally Hell on Earth.
Courtesy chensiyuanGrand Canyon, could you please show us your birth certificate? A new theory that parts of the Grand Canyon were carved as far back as dinosaur days has geologists picking sides on a controversy. New research contends that the western end of the canyon might be up to 70 million years old, carved by an ancient river that flowed in the opposite direction of today's Colorado River. Conventional theories about the canyon had its aged pegged at 5 to 6 million years old.
So what do you think?
Courtesy USGS/Earthquake Science CenterA court in Italy has sentenced six scientists and an ex-government official to six years in prison for failing to properly warn the public about a devastating earthquake that killed 309 residents of the town of L'Aquila in 2009. The seven defendants were convicted of manslaughter and also ordered to pay for damages and court costs.
I think the court itself has failed to predict just how idiotic this irrational prosecution looks to the world scientific community. Let's hope an appeals court will be reasonable enough to override this terrible injustice.
All this week is Earth Science Week, a time for celebrating the importance and relevance of the earth sciences. Above is a cool little video produced by the American Geosciences Institute (AGI) that does just that. The website EarthSky.org (where I found this video) lists Nine Big Ideas to ponder and share during the week. Additional ways to celebrate can be found at the official Earth Science Week website. And don't forget, Wednesday, October 17 is National Fossil Day. Groups, museums, and other facilities around the country will be observing it on various days surrounding the official date. Here at the Science Museum of Minnesota we'll be celebrating both fossils and earth science on Saturday, October 20 from 1pm-4pm. Join us for activities around the museum where you can learn about Twin Cities fossils, fossil prep, fossil research, trilobites and more.
Courtesy US Geological SurveyThis cool graphic from the USGS Water Science School website gives you a really good idea of just how much water there is on Earth. Compared to the Earth itself, it doesn't look like much. The large blue globe represents the volume of all the water present on Earth, i.e. in the oceans, lakes, icecaps, atmosphere etc. The next size is the volume of the all fresh water - much of which is located underground. Don't overlook the very tiny blue globe positioned beneath the mid-sized water globe and just northwest of Florida in the graphic. That's how much fresh water is contained in all the lakes and rivers on Earth - the sources of life's drinking water. Feeling thirsty now?
The mission of NFD is to “promote public awareness of fossils as well as to foster a greater appreciation of their scientific and educational value.”
This year the official day falls on October 17, but celebrations take place at various locations around the country over several days. Here at the Science Museum of Minnesota, the day will be celebrated on Saturday, October 20, 1pm-4pm throughout the museum. You can see what events are happening in your own area here.
Besides going out and hunting for fossils, one of my favorite NFD activities is the National Fossil Day Art & Photography Contest. As in previous years, the competition is open to anyone across several age groups. This year’s theme is “Careers in Paleontology”. A panel of NFD partners and paleontologists will select the winning entries. I’ve already sent in my submission but you have until October 5th (postmark deadline) to enter your own masterpiece.
National Fossil Day is usually observed in conjunction with Earth Science Week and this year is no different. EWS occurs October 14-20, and this year’s theme is Discovering Careers in the Earth Sciences.
Check out this incredible video taken at the edge of a lava lake produced by Marum Volcano on Ambryn Island, Vanuatu near New Guinea. The astounding video was shot by Geoff Mackley, Bradley Ambrose, and Nathan Berg. I'm not sure which of them is in the suit posing at the edge but what a view he must have had! Apparently, without the heat-proof suit and breathing gear, you could only get within 30 yards of the boiling lake, and endure just six seconds of the blistering heat. The protective gear allowed the wearer to stand at the edge for 40 minutes! How cool would that be?
Courtesy NASA/JPL-Caltech/MSSS/Ed TruthanMeanwhile, back on Mars, the Curiosity rover has sent back some very cool close-up photos of an intriguing rock outcrop it found on the Red Planet's surface. My first impression looking at the image (which is comprised of several shots stitched together by graphic designer Ed Truthan) is that it looks like it's made up made up of cobbles, and pebbles and sand - the same kind of deposit you find here on Earth left by an old river channel.
A photograph captured by the Mars rover, Curiosity, shows an unconformity in the strata of Mount Sharp, a mountain inside nearby Gale Crater. An unconformity is a geological feature marking a stop in sedimentation and erosion of a surface before the overlying layer is deposited. The photo above shows the two distinct rock layers (marked by a line of white dots) that make up the unconformity. The upper layer, which is tilted left to right in relation to the lower layer, contains no evidence of hydrated minerals found in the lower layer. This idicates the two layers were laid down in different environments.