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As a SciShow viewer, you can keep building your STEM  skills with a 30 day free trial and 20% off an annual premium  subscription at Brilliant.org/SciShow. 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. [INTRO] 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.

And because diatom frustules persist for so long, and there are so many of them  kicking around in bodies of water, their remnants deposit themselves to  make vast layers of silica-laden sand. That sandy silica made of  diatom corpses is precisely what you can buy at the hardware  store as diatomaceous earth! And all of those properties of  silica that we just mentioned come together to deliver a fatal blow to bugs.

For starters, the tiny size of diatoms  means that the silica particles can easily stick onto the exoskeletons of passing  insects that come into contact with it. Once they’re on there, the remarkable  moisture sucking property of silica takes hold and absorbs the oils and fat on the  insect’s soft outer shell, breaking it apart. And, all those sharp edges start to  cut up the bug’s cuticle pretty badly, which breaks it open and allows the water  out of the insect’s body until it dehydrates!

After getting cut up and dried,  creatures like slugs, beetles and worms crawling along your prized  petunias won’t get very far. And while this is pretty gruesome for  the insect, the way diatomaceous earth works is mostly mechanical, meaning  it relies on physically hurting an insect rather than trying to  poison it with toxic chemicals. All in all, this could be much kinder  to the surrounding environment than other kinds of pesticides that can  wreak havoc in the local ecosystem.

It’s kind of fascinating that these  fossil organisms have evolved for millions of years and became incredible  pest-killers, basically by coincidence. But like we said at the beginning,  we have found uses for diatoms well beyond gardening and insect-killing! There are lots of places where  the humble diatom’s absorbing, durable and scratchy frustule finds a purpose.

For instance, that great absorption  quality means that diatomaceous earth often finds its way into cat litter.  It’s excellent at soaking up those interesting smells that your cat  leaves in the tray when it is in there. And in the food industry, diatomaceous  earth is used to absorb contaminants from certain products, helping to  purify and filter out unwanted liquids in the process of making vegetable  oil, sugar, syrup, wine and even beer! Those frustules’ tough, pointy exteriors  come in handy as a kind of abrasive, too.

Diatom frustules are great for smoothing down and polishing metals like bronze and aluminum, and even ceramics like marble and glass. But maybe the place you might least  expect to find millions of years old fossils of algae cell walls is as  hidden nanotechnology components. Take the field of plasmonics, where  researchers need to create tiny optical and electrical components,  just a few molecules large, which can manipulate light signals on tiny scales.

These have a whole host of applications  from telecommunications to things like chemical sensing, biomedicine  and even quantum computing! As great as that all sounds,  and it does sound great, the hard part is often actually  creating nanoscale components with intricate patterns capable of  manipulating light in the required way, such as tiny well-organized structures  that can refract and reflect light. But guess what happens to form  in tiny, sturdy geometric shapes?

Yes, diatoms. Silica, as we mentioned, is basically  just glass that can refract light in a way that plasmonic nano-components need. But the real magic happens when  you combine diatoms with metal.

Coat a bunch of diatoms with a light  dusting of silver nano-particles, and you can make a surface that detects  the presence of certain chemicals. For instance, the illegal food additive  melamine can lead to kidney disease and even death, so knowing when food  is laced with it is pretty important. In a 2016 study at Oregon State  University, researchers dropped melamine laced samples onto a  silver and diatom coated surface and shone a laser on it to  measure the spectrum of light that was refracted off of that surface.

In the presence of melamine, the  spectrum had a tell-tale fingerprint that indicated the presence of the offending molecule! Basically, if there’s melamine on the sensors,  the reflected laser signal can pick it up. And, those same diatoms could  detect the compound Xylene, which pollutes air, water and soil and irritates  your skin if you encounter a lot of it.

Not only that, the diatom  sensor did a better job at detecting Xylene than their other technique! Admittedly, this is pretty early  days for this kind of technology. But it’s well within the realm of possibility  that diatom sprinkled nano-sensors could be monitoring many aspects  of our environment before long.

From pollutant detection to pest protection,  there’s not much we can’t do with diatoms. We owe a lot to those funky little  guys, just doing their thing and making their little silica houses. But just like the packet says, they  still don’t make a very good snack, nobody’s perfect.

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