What happens to diatoms’ shells when they die?
When diatoms die, their shell, the frustule, is not eaten and does not decompose, instead it sediments and accumulates to the bottom of the water. When that happens for millions of years in a lake or a sea, the accumulation of billions of diatom frustules forms a layer at the bottom of it. In some places those seas and lakes are not there anymore, they dried out, making the deposits of frustules, called diatomaceous earth (DE), available for extraction.
The DE was first discovered by Peter Kasten in 1836 in Northern Germany. The region has been exploited for DE since then, but since the first world war extraction has occurred all over the world, from the USA, to the Czech Republic, from China to Algeria and Mexico.
The very first significant impact of DE use was developed by Alfred Nobel. He discovered that nitroglycerin, a liquid explosive, when mixed and absorbed by DE becomes more stable, which makes it much safer to transport. He patented the mixture and called it dynamite in 1867. The same absorbance capacity of DE is used in the production of pets litter.
Another important discovery was made around 1890 by Wilhelm Berkefeld. He discovered that thanks to the porosity of DE, if pressed into a cylinder, it could act as a filter for water. He called them filter candles. They helped fight the cholera epidemic in Hamburg, Germany, in 1892. Since 1950, filter candles are also used to clarify beer, and other forms of the same filtering capacity are used for swimming pool filters, fish tanks filters, and also in laboratories.
Abrasion is another characteristic of frustules that has been exploited for decades, as a component of toothpaste and as a natural effective pesticide in agriculture. Indeed the abrasion capacity of DE damages the lipid layer on insect exoskeleton, modifying its permeability and making the insects vulnerable to dehydration.
Quite recently, a new discovery brought diatom’s frustules to a new light. In their beautiful and intricate structure there are innumerable tiny holes that interfere with the direction of light waves. This means that looked at from different angles, the same structure assumes different colours. It is called iridescence. Mixed to paint and other materials, DE could bring the power of iridescence to make-up and fabric, but it could also be used by engineer to enhance the efficiency of solar panel to capture solar energy.
Diatoms are amazing!