Every day, a fine sprinkling of dust covers your city or farm, landing across the roof of your house or onto the hood of your car. Some of it may settle in your hair, or onto the vegetables you eat in your salad. If you take a closer look, you’ll notice it isn’t just any dust – it’s oddly metallic and finely grooved.
And it’s from outer space.
Every year, somewhere between 40 and 80 thousand tons of extraterrestrial material falls to Earth. That’s equivalent to the weight of five to ten Sears Towers. The majority of this material comes in the form of tiny “micrometeorites,” which can be as small as one tenth of the width of a human hair. Enthusiasts around the globe collect samples from rooftops, sifting through exhaust particles and bits of cement to find and photograph these tiny cosmic visitors. But many don’t realize that similar extraterrestrial matter, from microscopic space dust to asteroids several miles across, has changed the course of history.
You might remember one of the more recent (albeit not hugely impactful) meteorites to cross the sky. On one morning in February 2013, thousands of car dash cams and phone cameras caught the dramatic fireball that streaked across the sky over Chelyabinsk Oblast in southwestern Russia. More than a thousand people were injured and more buildings were damaged by the powerful shockwave produced when a city bus-sized asteroid exploded in midair. The thousands of videos went viral on the internet, and their sheer volume made this particular event the best-documented extraterrestrial “impact” in history.
I use the term “impact” generously here. When a meteorite explodes in the atmosphere, it’s called an “airburst.” A similar such airburst occurred over 100 years before the Chelyabinsk event, also over Russia. This airburst was named the Tunguska Event after a nearby river. The meteor in question was triple the size of the Chelyabinsk object, but produced the largest impact event ever witnessed by humans. Releasing the energy of 1,000 atomic bombs, the explosion flattened an area equivalent to the area of three Chicagos. People as far away as England felt the Earth shake. The blast was large enough to have destroyed entire cities, but by a stroke of dumb luck, the impactor exploded above remote Siberia and nobody was harmed – save for some unfortunate wildlife and about 80 million trees.
Though the Tunguska event was powerful, it’s nothing compared to the biggest impacts we’ve found evidence of in Earth’s geological record. The most famous occurred about 66 million years ago, when a six-mile-wide asteroid struck what’s now Mexico’s Yucatan Peninsula with the force of a billion atomic bombs. This impactor left a crater the size of Maryland in what happened to be soft, sedimentary rock. The impact ejected these sediments into the atmosphere, where they eventually enveloped the globe. This debris cloud effectively blocked light and heat from the sun, causing extended global cooling and rendering many environments uninhabitable. To add insult to injury, the sediments reacted with water vapor, producing extremely acidic rain.
This presented a problem for the inhabitants of Earth at the time. Though initially a highly controversial theory, it’s now widely accepted among the scientific community that the extended impact “winter” was the primary driver of the fifth mass extinction, in which three-quarters of all species perished; most notably, the dinosaurs. A tragic consequence of such an unlucky, random event. But when these millions of species disappeared, they opened ecological niches that mammals evolved to fill. Has this not happened, mammals may never have risen to prominence and we may never have existed! In a way, we can thank this unlucky, random event for our presence here on Earth.
Though the catastrophic events I mentioned are the most well-known and perhaps the most exciting to think about, cosmological and geological processes usually operate on timescales beyond our comprehension. It follows that much of the overall accumulation of extraterrestrial matter on Earth has been similarly slow and steady, much like the dust falling in our backyards today.
For example, far earlier in Earth’s history, well before the dinosaurs, even before the planet hosted life, a heavy accumulation of extraterrestrial matter likely varnished the surface with enough asteroids, comets, and space dust to cover the globe in a ten-mile-thick blanket. Many scientists believe that this “Late Veneer” is to thank for the presence of heavy elements in the Earth’s crust today, as the original metals had long since sunk to the core. The Late Veneer may hold the answer to another problem in our understanding of Earth’s history: the origin of the abundance of volatiles, or chemicals that can easily turn into gas and float around into our atmosphere. These chemicals, including carbon, nitrogen, and water, are the keys to the existence of life as we know it.
It’s widely accepted that the inner planets in our solar system (Mercury, Venus, Earth, and Mars) were “dry” when they formed; they didn’t house any volatiles because young planets were too hot to hold onto them. Later, volatiles were introduced by objects that originated further away from the sun, where it was cool enough that water ice could form and survive. These objects were likely a mixture of “wet” (volatile-rich) meteorites and comets.
Comets are icy bodies that form a characteristic tail of gases that get released when they pass close to the sun. Scientists favor the theory that comet impacts are what brought volatiles to Earth during the Late Veneer, bringing us oceans, the atmosphere, and maybe even life. Studies suggest that these comet impacts could have favored linear peptide synthesis, a process that is necessary to form amino acids, the building blocks of all life on Earth – life including you and me. This kind of protein-building is only possible at the lower temperatures that geologists think dominated early Earth. All life, from the tiniest microbes to human beings, may only exist due to the impacts of particularly wet celestial bodies on Earth billions of years ago.
Today, scientists continue to collect and study extraterrestrial matter that falls into our world. They search for clues about the history of our Earth, our solar system, and the universe beyond. Fortunately, researchers have found easier ways to do so than to sift through the dust on our roofs or park benches. One option is to explore the South Pole.
Near the South Pole, the closest soil is literally miles away. So if you discover any natural dust, you’ve discovered space dust. Antarctica, then, is a prime location for collecting cosmic particles. Here, researchers have built vacuums (just like your vacuum cleaner at home) in research station wells and giant air suckers atop remote plateaus to trap the alien grains.
But you need not travel far to find yourself immersed in space dust. If you ever find yourself with access to a microscope and a good amount of time on your hands, you too could see the very same micrometeorites anywhere you choose to look. After all, the celestial bodies that fell to Earth millions of years ago may have dramatically paved the way for our species’ presence. Perhaps the tinier cosmic visitors from billions of years ago eventually became the molecules that make up you. Who knows what today’s visitors may become?
Katarina Keating is a student at the University of Chicago studying Geophysical Sciences and Creative Writing. She works as a research assistant in the planetary sciences, focusing on the early climate of Mars. She also enjoys hiking, biking on the Lakefront Trail, and dreaming of being the first human on Mars. You can find her at LinkedIn or email her at kakeating [at] uchicago.edu.
Katarina’s article is part of a collaboration between the Illinois Science Council and the University of Chicago.