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When you think of the places fossils are found, you probably are imagining a museum, an excavation pit in the desert, maybe even, like, a beach. But head to your local hardware or gardening store, and you can probably buy fossils by the millions. Alongside the pesticides and roach traps, you’ll find bags of diatomaceous earth, a white, powdery substance that’s a great, nontoxic method for killing bugs. If you got there, and you pick that up, what you are holding is actually a big bag of fossil algae called diatoms. And millions of years after these little animals died, we are using these fossils to do a lot more than kill ants.
Diatoms turn out to be great for everything from cleaning up cat pee to building nanotechnology. The term “diatom” refers to lots of different kinds of phytoplankton, a sort of single-celled algae that lives in lakes and oceans. Diatoms first evolved some time in the late Jurassic period, about 160 million years ago. These primeval plankton are only about as big as the width of human hair! And today, there are at least twenty thousand different species of them around. In fact, scientists suspect there could be as many as millions of kinds of diatoms, since we keep discovering new kinds every year.
What diatoms lack in size, they make up for in their enormous presence in the world. So much so that their combined photosynthesis produces something like a quarter of all the oxygen in the atmosphere. So, if nothing else, we have diatoms to thank for the literal air we breathe! But hiding behind this biological benevolence are the makings of a secret killer.
Take a look under a microscope and you’ll see all kinds of strange and beautiful shapes. As we mentioned, there are a lot of different types of these critters! And their ethereal beauty comes down their cell walls, which are there for more than just looking cool. The cell walls of a diatom are made up of frustules: sturdy barriers made of the material silica, which they produce from the silicic acid floating about in the water around them. And that silica is basically the same stuff as glass, which is what makes a diatom’s cell walls so durable, and also mega-pretty. So diatoms definitely should not throw stones, they are literally living in glass houses.
As well as providing a cozy little home for a diatom, silica frustules have some pretty funky properties as a mineral. Despite the reputation of glass as a fragile material when it’s in a large, thin pane like a window, silica is actually pretty strong as far as materials go. And that silica has another unique property, which is the reason you might encounter it at the bottom of a shoebox. You know these tasty little DO NOT EAT packets? That is silica! Not eating silica, by the way, is great advice because those beads are a major choking hazard and can totally mess up your respiratory system and digestive tract! So, again, like it says, do not eat.
So those tiny beads of silica are actually there because silica is amazing at absorbing moisture! Materials like these with moisture sapping superpowers are called desiccants. They are great for preventing mold forming on all that porous material, like the kind your sneakers are made out of. And, as little water-sucking sponges, they come in handy for all kinds of situations, as we will see in a moment.
The final trick up silica’s sleeve is the fact it’s inorganic. While “normal” fossils are made as minerals replace harder bits of an animal’s remains, like bones, diatom frustules don’t dissolve or get broken down by smaller organisms. So diatom fossils are basically identical to diatoms you’d find around today, just, you know, empty and dead. The results showed that the surface was able to detect the presence of melamine in food samples with a remarkable degree of accuracy.
Diatom frustules persist for a long time and are present in large amounts in bodies of water, depositing themselves to create sandy silica made of diatom corpses, which is available at hardware stores as diatomaceous earth. This earth is a great pest killer, as its tiny size and sharp edges can stick onto the exoskeletons of passing insects, absorb the oils and fat on their outer shells, and cut up their cuticles, leading to dehydration. It is a mostly mechanical process, and is kinder to the environment than other pesticides. Diatoms have also been used in cat litter to absorb odors, in the food industry to purify and filter liquids, and as an abrasive to polish metals and ceramics. They also have applications in plasmonics and nanotechnology, as their frustules can refract and reflect light and coatings of silver nano-particles can detect certain chemicals. In the presence of melamine, the spectrum had a tell-tale fingerprint that indicated its presence. The same diatoms could detect the compound Xylene, which pollutes air, water and soil and irritates skin. Furthermore, the diatom sensor was better at detecting Xylene than other techniques. This technology is still in its early days, but it’s possible that diatom-sprinkled nano-sensors could be monitoring many aspects of our environment soon. From pollutant detection to pest protection, diatoms can be used for many applications. We owe a lot to these tiny creatures and their silica houses.
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