Heritage went to the Sheffield on August 20th and the 21st to help out with the excavation. We learned how to screen for artifacts, measure the depth of our unit using datum points, and we learned how people use the data from geophysics to select where we should dig.
Courtesy Science Museum of MN
Screening for artifacts is when we sift through the dirt we dug from our unit. We use a tool called a screener that lets the loose dirt through so we can see the artifacts better. To get rid of the clumpy dirt we pushed it through the screen with our hands. The first unit we were at was called Block Two and we found a lot of artifacts in that unit. We learned how to recognize what was an artifact and what was not. Lithics, or stone that have been worked, have a sharper edge and a distinct pattern when it is shaped. Bone fragments are usually lighter in color than most of the items on the screener and you can see holes that are porous spots in them that make bones lighter in weight. To identify pottery they have a certain color on one side and a different one on the other side. When you look at pottery fragments from the side it looks like it has layers and the outer and inner faces of the pottery are flat. Sometimes you see small indents in the pottery meaning that it was tempered but the temper decayed away.
Courtesy Science Museum of MN
When we are digging in a unit we have to dig across and go down layer by layer. To make sure we stay level as we dug we use a datum point. A datum point is a point we designate to measure from. We tie a string to the datum point and to make sure it’s always level to the datum point there is a line level attached to it. To measure the depth of our unit we made sure the string is taut and nothing is obstructing its path, then we take a tape measure and put it perpendicular to the string and then take the measurement in centimeters. We record the unit every time we dig down ten centimeters by taking pictures and drawing sketches of the unit.
Courtesy Science Museum of MN
Geophysics is where we collect data from the ground to choose where a likely spot to dig would be. One of the machines used to determine the locations of the Sheffield units looks at the electrical resistance in the ground. Less resistance usually indicated that the ground was dug up and refilled. Resistance low areas might have been a fire pit or other settlement features thus making it a good site to look for artifacts. Another machine can spot magnetic differences in the ground. Dirt has different magnetic outputs from rocks and artifacts. One area of the site has a very different magnetic output so the team decided to put block three in that area to dig there. The last method we used to determine the location of our units was using lidar technology. Lidar is where you use shine light on an area and study how the surface reflects to map out the surface of the area.
Courtesy Science Museum of MN
Overall, I had a lot of fun at the site especially when I found pottery. I find pottery more interesting than lithics or bone for reasons I do not know why. It was really hot and humid but no one passed out so it was fine. Before we started digging we helped sift through the dirt in block two and we found a lot of pottery and debitage, or flakes, from stone tools. We even found an intact arrow point. We were assigned to dig in Block 3 where the magnetic anomaly was, but we only found one fragment of pottery and the rest were roots and rocks so digging there wasn’t so exciting. Learning from Ed, Jasmine, Mary, and Anne on the field has been very fun. I can understand why they like doing this for a living.
Courtesy Mark RyanNext week the Geological Society of America is convening in Minneapolis, Minnesota for the GSA's 2011 Annual Meeting and Exposition. That means something like 6000 geologist, paleontologist, hydrologists, and other ologists from around the world will be in our area to share new ideas and hobnob with their fellow earth scientists. The four-day event, which is hosted by the Minnesota Geological Survey, runs from Sunday, October 9 through Wednesday, October 12 at the Minneapolis Convention Center, and will include special lectures, award ceremonies, poster sessions, an exhibit hall, and several hundred technical talks covering a full range of geology-related subjects. There will also be a silent auction, a photo exhibition, short courses (available to non-registrants), and a screening of the locally produced documentary, “Troubled Waters: A Mississippi River Story”. Field trips happening before, during, and after the official meeting dates will give visiting geologists an opportunity to take in some of the spectacular and diverse geology that Minnesota and the Upper Midwest has to offer, not to mention the fall colors. This year’s meeting is titled “Archean to Anthropocene: The Past is the Key to the Future”, and even if you can’t make it to Minneapolis, you can download a cool poster of the event here.
You’d probably say, “Huh?? Hold on, what is geothermal energy anyway, and how does it work?”
Geothermal is heat from deep inside the earth. Because heat is a form of energy, it can be captured and used to heat buildings or make electricity. There are three basic ways geothermal power plants work:
(Click here for great diagrams of each of these geothermal energy production methods.)
“And what about carbon sequestration too? What’s that and how does it work?”
Courtesy Department of Energy
Carbon sequestration includes carbon (usually in the form of carbon dioxide, CO2) capture, separation, transportation, and storage or reuse. Plants, which “breathe” CO2, naturally sequester carbon, but people have found ways to do it artificially too. When fossil fuels are burned to power your car or heat your home, they emit CO2, a greenhouse gas partially responsible for global climate change. It is possible to capture those emissions, separate the bad CO2, and transport it somewhere for storage or beneficial reuse. CO2 can be stored in under the Earth’s surface or, according to Martin Saar’s research, used in geothermal energy production.
Alright. We’re back to Professor Saar’s research. Ready to know just how he plans to sequester carbon in geothermal energy production?
It’s a simple idea, really, now that you know about geothermal energy and carbon sequestration. Prof. Saar says geothermal energy can be made even greener by replacing water with CO2 as the medium carrying heat from deep within the earth to the surface for electricity generation. In this way, waste CO2 can be sequestered and put to beneficial use! As a bonus, CO2 is even more efficient than water at transferring heat.
But don’t take my word for it. Come hear Professor Martin Saar’s lecture, CO2 – Use It Or Lose It!, yourself during the Institute on the Environment’s Frontiers on the Environment lecture series, Wednesday, October 27, 2010 from noon-1pm.
Frontiers in the Environment is free and open to the public with no registration required! The lectures are held in the Institute on the Environment’s Seminar Room (Rm. 380) of the Vocational-Technical Education Building on the St. Paul campus (map).
Courtesy Joe HatfieldGeochemists at UCLA have determined plate tectonics – the theory involving the movement and collision of crustal plates – began much sooner after the Earth’s formation 4.5 billion years ago than thought previously.
Until now, plate tectonics were thought to have begun around 350 million years ago - or even later – but this new UCLA data points to much earlier beginnings.
"We are proposing that there was plate-tectonic activity in the first 500 million years of Earth's history," said professor Mark Harrison, director of UCLA's Institute of Geophysics and Planetary Physics and co-author of the paper. "We are reporting the first evidence of this phenomenon."
Their report appears in the science journal Nature.
The theory of moving crustal plates floating on molten rock was first championed in Alfred Wegener’s 1912 work, The Origins of Continents and Oceans. Wegener suggested all the continents existing today originated in a super-continent he called Pangaea that spread apart over time due to “continental drift”. Most scientists were skeptical of the theory until the 1960s when it was bolstered by the discovery of sea floor spreading.
Harrison and his colleagues analyzed zircon crystals found in 3 billion year old rocks from Western Australia. The rocks were formed from ancient magmas that had cooled and froze the mineral crystals in place. Using an ion microprobe, they bombarded the zircon with a beam of charged atoms (ions). The bombardment caused the zircon crystals to release their own ions and these were then analyzed using a mass spectrometer. The analysis showed the zircon crystals were more than 4 billion years old. It also showed the zircons had formed in an area where the heat flow was much lower than expected.
"The global average heat flow in the Earth's first 500 million years was thought to be about 200 to 300 milliwatts per meter squared," said Michelle Hopkins, a UCLA graduate student in Earth and space sciences, and the study's lead author. "Our zircons are indicating a heat flow of just 75 milliwatts per meter squared — the figure one would expect to find in subduction zones, where two plates converge, with one moving underneath the other."
The only places on Earth today where the average heat flow is one third that of the rest of the planet are in convergent plate-tectonic boundaries where magmas are forming.
Harrison published an earlier study in 2001 proving water was present early on the surface of the Earth during its formative years, and this current data strengthens his claim because plate tectonics can’t occur on a dry planet.
All this new information forces scientists to reevaluate their conception of how Earth appeared early in its formation.
"Unlike the longstanding myth of a hellish, dry, desolate early Earth with no continents, it looks like as soon as the Earth formed, it fell into the same dynamic regime that continues today," Harrison said. "Plate tectonics was inevitable, life was inevitable. In the early Earth, there appear to have been oceans; there could have been life — completely contradictory to the cartoonish story we had been telling ourselves."