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July 23, 2012

As we work to develop materials, we often overlook the fact that real world materials are quite unlike the 99.999% pure chemicals we use in our laboratories. When our new materials leave the laboratory and become production items, there are a myriad of things that can go wrong because the lesser grades of materials used to compound a product may have important impurities. As an example, sulfur is one impurity that leads to corrosion problems with high temperature superalloys.

We forget that nearly every inorganic chemical we use is dug from the ground and is somehow refined to the point at which it contains just one, or a few, elements. However, there are some things that are just dug from the ground and used as-is. One example is kieselguhr, more commonly known as diatomaceous earth.

Aulacodiscus Grevilleanus (after Ernst Haeckel)

Nature Imitating Art

The diatom, Aulacodiscus Grevilleanus, as drawn by Ernst Haeckel (1834 - 1919).

Haeckel was an eminent German biologist and artist. He discovered and named thousands of species.

(Via Wikimedia Commons))

Diatomaceous earth consists of the silica-rich fossil shells of diatoms, a type of algae (See figure). The fossil remains are laid in thick sediments, and they are composed of a useful mixture of silica (SiO2, 80-90%), alumina (Al2O3, 2-4%) and iron oxide (Fe3O4, 0.5-2%). Diatomaceous earth is used, not surprisingly, as an abrasive.

Diatomaceous earth is also used for filtration, a filler for plastics, and a support medium for catalysts. Its absorbency makes it useful for cat litter, and that's how the Nobel Prize and the family cat have something in common. Alfred Nobel made his fortune by mixing nitroglycerin and diatomaceous earth to form dynamite, a stable explosive. As can be expected from its composition, diatomaceous earth is a good material for thermally insulating high temperature furnaces.

The most important material to be dug from the ground and used in its pristine state is coal. Coal fueled the Industrial Revolution, and about 45% of electrical generation in the US in 2009 was from coal. The use of coal, however, declined from 52.8% in 1997. The former prominence of coal-fired power plants is because coal is cheap. The current decline is because the burning of raw coal damages the environment.

The environmental damage isn't just from the carbon dioxide building up in the atmosphere, it's from the impurities in coal. The sulfur dioxide formed in combustion of the sulfur impurity in coal causes acid rain when converted to sulfuric acid in the atmosphere. Coal also contains significant quantities of mercury; so much so, that many tons of mercury are injected into the atmosphere from coal combustion each year.

If it wasn't for coal, our lives would be quite different. So, what's the origin of coal? Coal is the fossilized remains of plants that lived about 300-360 million years ago.[1] What was fossilized was mostly lignin, a complex polymer that's a part of the cell walls of plants. Lignin serves to give wood its robust mechanical properties. The deposition of coal came to an abrupt end at the aptly-named Carboniferous period. Why did this happen?

A research study by a team of 71 scientists from twelve countries,[2] funded by the National Science Foundation and published in the June 29, 2012, issue of Science,[3-4] suggests that white rot fungi evolved at the end of the Carboniferous with the capacity to digest lignin.[2] White rot might be the factor that ended the sixty-million year span of coal deposition, since it may have single-handedly destroyed the accumulation of woody debris that would have fossilized as coal.[2]

Wood rot micrograph

A scanning electron micrograph of wood that has been decayed by white rot. The rot has largely destroyed the wood structure.

(NSF photo, Robert A. Blanchette / Joel A. Jurgens, University of Minnesota))

David Hibbett, a Professor of Biology at Clark University, led the research team.[2] Hibbett is an acknowledged expert on fungi, and Clark University maintains the Clark Fungal Database. The team looked at the genomics of fungi known as Basidiomycetes, which include white rot fungi.[1] They compared 31 fungal genomes, 26 of which were sequenced at the Department of Energy's Joint Genome Institute.[2]

The team did a "molecular clock" analysis of genome mutations that traced the lignin-degrading ability back about 290 million years.[2] Says Hibbett,
"Our results suggest that the ability of fungi to break down lignin evolved only once."[2]
The same organisms that ended the production of coal might be able to help with our future energy requirements. The fungal genomes might offer the basis for development of fungal species for biofuel production. These would break down lignin of woody plants, releasing cellulose from cell walls that could be fermented into sugars. These sugars would then be used for production of alcohol by yeast for biofuel.[2] Fungi may also be used for bioremediation, since they can break down complex organic molecules.[2]

Says Joseph Spatafora, a professor at Oregon State University and a co-author on the study,
"There's an estimated 1.5 million species of fungi... We have names for about 100,000 species, and we're looking at 1,000 fungi in this project. This is still the tip of the iceberg in looking at fungal diversity and we're trying to learn even more to gain a better idea of fungal metabolism and the potential to harness fungi for a number of applications, including bioenergy. It's a really exciting time in fungal biology, and part of that is due to the technology today that allows us to address the really longstanding questions."[1]


  1. Tracking the Remnants of the Carbon Cycle: How an Ancestral Fungus May Have Influenced Coal Formation, Joint Genome Institute Press Release, June 28, 2012.
  2. Study on Fungi Evolution Answers Questions About Ancient Coal Formation and May Help Advance Future Biofuels Production, NSF Press Release 12-117, June 28, 2012.
  3. Chris Todd Hittinger, "Endless Rots Most Beautiful," Science, vol. 336 no. 6089 (June 29, 2012) pp. 1649-1650.
  4. David S. Hibbett, et al., "The Paleozoic Origin of Enzymatic Lignin Decomposition Reconstructed from 31 Fungal Genomes," Science, vol. 336 no. 6089 (June 29, 2012) pp. 1715-1719.
  5. The Hibbett Laboratory at Clark University.
  6. David Hibbett, "Evolutionary Perspectives on Diversity of Lignocellulose Decay Mechanisms in Basidiomycetes" at the 7th Annual Genomics of Energy & Environment Meeting on March 21, 2012 in Walnut Creek, CA.

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