Antarctic Meteorites. Molly Reardon ES 567 Final Project Spring 2010 http://www.emporia.edu/earthsci/ amber/go340/students/reardon/. Project Presentation Overview.
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ES 567 Final Project
I am a graduate student at Emporia State University in Earth Science. This project was for my gemstone course, www.emporia.edu/earthsci/amber/go340, and includes:
For comments or questions,
There is not one generally accepted definition for “gemstone”, however, they all have something unique about them. In the case of meteorites, their origin is what sets them apart from other gems we’ve studied in this course.
- It’s a fragment of a space rock that lands on Earth as the result of a collision or impact between two parent rocks.
- Some have lunar or Martian origins, but most originate from the asteroid belt.
- Meteoritic events that are witnessed are called a “fall”, while meteorites that are stumbled upon are called a “find.”
- Meteorites are usually named after the person who discovered them or after the closest town or geographic landmark.
- More meteorites have been found here than on any other continent.
- A special concentrate mechanism exists to explain why so many different meteorites are found on the ice.
- Antarctica is an amazing place to talk about and study!
- In the early 1970’s, at a Meteoritical Society meeting, http://www.meteoriticalsociety.org/, Japanese scientists described finds of 9 different kinds of meteorites in one area in Northeastern Antarctica.
- Until this point, meteorites concentrated in one location have always been from the same fall.
- Meteorites found on the ice by expeditions dating back to 1911 were not realized to be significant. It was unknown these rocks were parts of much larger “strewn fields”.
- Thousands of years ago, meteorites fell to earth and became embedded in the Antarctic Ice.
- As the glacial ice flowed downstream from the interior of the continent to the coastal regions, it carried embedded rocks and debris with it.
- Sometimes the ice encounters a barrier or stagnation point, such as a mountain range or a subsurface ridge. When ice stops flowing at stagnation points, it evaporates or ablate.
- The rocks and debris embedded in the ice at these stagnation points will gradually make their way to the surface as the ice they are contained in ablates.
- We are then left with a concentration of rocks in one location; most of which come from varying sources and started their downward journey at different times. (See image on next slide)
- To determine potential collection points and concentration areas, ANSMET scientists study the US Geologic Survey's archive of aerial and satellite photos of Antarctica in Reston, Virginia.
- They are specifically looking for direction of ice flow marked by crevasse fields and potential boundaries such as mountains and subsurface ice ridges.
- Once on the ice, the scientists branch out to potential areas of interest and set up a field camp.
- The field seasons occur during the Austral Summer, between October and February of each year. The climate is too harsh to be outdoors during the winter months. Summertime temps can range from -55F up to 0F. Summertime has the added benefit of 24/7 sunlight. So scientists can work round the clock!
Image obtained from:
- Depending on location, meteorite searches conducted on foot or skidoo.
- Skidoos used to cover large areas of open ice where only a few rocks are present.
- On-foot searches conducted in glacial moraines where many rocks are present, and distinguishing between earth rocks and meteorites requires a closer look. A typical method is 5-6 people to be spread out over 30-40 meters and to search ground in a series of sweeps.
Image obtained from:
- If a rock is suspected to be a meteorite, it is put into collection kit
- The kit contains “sterile bags to put the meteorites in, numbered tags to label them with, tape to close and seal the bags, a notebook to take down any distinguishing features of the sample, and some scissors to cut the tape.” (http://geology.cwru.edu/~ansmet/collecting/index.html)
This image obtained from:
- Once the rocks are collected from the ice, the shipment processes begins.
- The rocks are kept frozen and packaged into coolers that are shipped to the Antarctic Meteorite Curation labs at the Johnson Space Center (JSC) in Houston, Texas
- At the labs, the rocks are carefully thawed and cracked open for study.
- The JSC classifies and assigns a name and number to the rock. Then they write a short description which is published in the Bi-Annual Antarctic Meteorite Newsletter, found here:
- Asteroid Belt
- A lunar meteorite is “a rock found on earth that was “ejected from the Moon by the impact of an asteroidal meteoroid or possibly a comet. ”
- By testing suspected meteorites for chemical compositions, isotope ratios, minerals, and textures, comparisons can be made to moon rocks collected on Apollo missions.
- Lunar meteorites found on Earth contain a fusion crust which is evident on the outside of the rock. This crust formed with deceleration through Earth’s atmosphere.
mineral, which is not known to be present on
other planets or our asteroid belt.
Image obtained from:
- A Martian meteorite is a rock that originated on Mars and as the result of some sort of celestial impact, has been ejected into the solar system and landed on Earth.
- Of the tens of thousands of meteorites that have been found on Earth, only a small fraction (less than 40) have been identified as originating from Mars.
- Asteroids are small planetary bodies that orbit our sun within the asteroid belt and pass between Jupiter and Mars. Occasionally, asteroids collide and rock remnants from the impact get pulled into the Earth’s atmosphere and fall to the ground.
- Meteorites with asteroid belt origins are the most common type found on Earth.
- The chemical composition of meteorites from the asteroid belt fall into one of three categories: Carbonoceous, Silicates, and Metallics. The presence of a fusion crust and chemical composition are what sets asteroid belt meteorites apart from Earthly rocks.
Image obtained from :
- Stony Irons
- Irons originate in the differentiated core of a planetary body and have extremely high densities.
- They contain varying amounts of nickel-iron masses.
- They are subdivided into three groups hexahedrites, octahedrites, and ataxites which are differentiated by the amount of nickel in each.
The tiny cube in lower right is 1cm X 1cm
Mesosiderites: contain equal parts of metallic nickel-iron and silicate.
Image obtained from: http://curator.jsc.nasa.gov/antmet/
Pallasites: contain olivine crystals of peridot quality in an iron-nickel matrix. You can see the olivine suspended in the iron-nickel in this image.
Image obtained from:
- These rocks are the most abundant type of meteorite found. They have been known to come from the Moon, Mars, and the asteroid belt.
- These rocks are suspected to have formed 4.56 billion years ago, after the formation of the sun.
- Stone meteorites consist of two subgroups: chondrites and achondrites.
close-up under polarized light of an
ordinary chondrite. You can see the gaseous chondrule
inclusions in the rock. Image obtained from: http://curator.jsc.
on Antarctica. Image obtained here: http://curator.jsc.nasa.gov/antmet/
- Although meteorites are not typically associated with aesthetically pleasing gemstones, they are being cut and fashioned using the cabochon style. Their unique origins set them apart from other gems with the exception of moldavite!
- Meteorites provide a glimpse into planetary geology and the possible formation of our solar system. These gemstones are extremely valuable for their geologic significance.
finds, it’s imperative that this research
continues and that some specimens
are preserved as gems!