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SEM image of the week: The iron-sulfur world

Posted on Monday, April 23, 2012 by for SEM.

Pyrite, also known as iron disulfide (FeS2), is a semiconductor which has nicknames such as fool’s gold. Pyrite’s metallic luster and appearance has earned it this name, but it is a lot lighter than gold. Ironically, pyrite is sometimes is found together with small quantities of gold. Pyrite’s original name comes from the Greek word for fire and was applied to any stone that would create sparks when struck.

Perhaps the most interesting thing about pyrite is not its ability to serve as a mineral detector, or its ability to produce sulfuric acid, or even its use by the paper industry. The most interesting thing about pyrite is the role it may have played in the origin of life. The iron-sulfur world theory proposed that pyrite, which is abundant near hydrothermal vents, reacted with carbon monoxide, hydrogen sulfide, and other inorganic gases under high pressure and high temperature to form organic compounds such as amino acids.

This SEM images below are part of our project to determine if pyrite could have played a role in the origin of life on earth. This project was originally proposed by Mr. Elert when we told him we wanted to do a project which investigates materials. After further research and input from Mr. Rosenfeld, I learned about the primordial soup theory and the iron-sulfur world theory. The primordial soup theory was proposed and tested by Stanley Miller and Harold Urey at the University of Chicago in the 1950s and involved exciting gases with electricity and heat to produce amino acids. However, this theory had its problems, the gases used in the experiment were not present in the early atmosphere and it would take a lot of luck to hit the right amino acids to produce the proteins. The iron-sulfide world theory proposed by Günter Wächtershäuser, a Munich patent lawyer, in the 1980s revolves around the role of iron pyrite as a catalyst in high pressure, high temperature environments to create amino acids.

Our project involves testing the iron-sulfur world theory by investigating the chemical and optical properties of pyrite. We wish to examine the surface of pyrite and later try to react pyrite with gases present in the early atmosphere under the right conditions to check if there is any reaction that could lead to production of amino acids, proteins, and even life.

Surface of the "inside". The pyrite was cut using a diamond cutter at Brooklyn College. Zoom in of one of the "caves" on the surface of the pyrite. There seems to be a lot of dirt, but those are actually inclusions of other minerals. Close up image of an inclusion, a chunk of foreign mineral stuck inside the pyrite. The edge of the pyrite. The "dirt" is actually sediments of pyrite and other minerals.
A crevice looking thing at the edge of the pyrite that seems to contain tons of dirt particles wanting to get off the pyrite. Surface of the "outside" pyrite. The original outside surface was bumpy, but we managed to smooth it out with sand paper. Notice the two major inclusions. A level view of the pyrite. The edges look pretty flat and parallel. Zoomed image of the surface. It doesn’t look so smooth now, does it?

Text and caption credit: Yao Jiang. Image credit: Yao Jiang and Tiffany Loi.

A few words about last week’s image of the week. It was a staple.