Humans have been around for a long time. We’ve seen and accomplished what might be thought of as miracles, but something in our nature doesn’t just let a miracle rest. When an amazing thing happens, we immediately set out to duplicate it. This is seen in how we judge scientific experiments (“Can the results be replicated?”) and is found on playgrounds everywhere. (“I bet you can’t do it again!”)

Some of our greatest, most difficult accomplishments have been repeated. When humans put a man on the Moon, we did it 11 times after that. Even some of the craziest oddities in nature have been witnessed more than once. Did you know the Mississippi River has flowed backward three times?

But occasionally, there are truly unique events—incredible things never seen again in recorded history. Here are ten.

10 Comet West

Visible in March 1976, Comet West, named after astronomer Richard West, who first observed it, was a remarkable sight that reached an apparent magnitude of –3. That’s brighter than Jupiter ever appears from Earth. While impressive, its place on this list is not because of its brightness but its orbital period.

Some comets are once-in-a-lifetime events, such as the famous Halley’s Comet, which orbits the Sun once every 76 years, but Comet West is estimated to orbit the Sun only once every 250,000 years. This figure is by no means certain; loss of mass or interactions with other solar bodies could change the comet’s orbit. Of course, 249,000 years is still a lot.

Regrettably, Comet West was not well-reported by the media. Prior to that, Comet Kohoutek had been hyped up but was a disappointing display, which led to Comet West’s lack of coverage. Some of us missed its visit in 1976, and we’re somewhat unlikely to see its next.

9 The Carrington Event

The Carrington Event was a geomagnetic storm caused by a massive solar flare at 11:23 PM on September 1, 1859. The flare was observed by Richard Carrington and hit the Earth’s magnetosphere the next morning, lighting the predawn sky with auroras seen as far south as Jamaica. Newspapers could be read in the light of these auroras.

More troubling was that telegraph wires the world over sparked and caught fire. Even when disconnected from their power sources, they were able to send messages because of the electrical currents caused by the event. Until that day, no one was aware that solar flares existed.

We routinely observe solar flares now, but the Carrington event was unique because of a combination of two things: It hit us, and it was massive, the largest solar flare to hit Earth in at least 500 years. If a similar event happened today, it would cause an estimated $1–2 trillion in damage. Here’s hoping it maintains its place on our list.

8 The Eradication Of A Human Disease

When the goal was set to eradicate smallpox in 1967, there were still an estimated 10 to 15 million cases a year, resulting in two million deaths and millions of disfigurements as well as leaving hundreds of thousands blind. It took more than a decade, but the last case of smallpox occurred in 1978, and the disease was declared officially eradicated in 1979. It is the only human disease to be completely eradicated from our population.

Prior to this, it had been a danger for 3,000 years and was only eradicated by the coordinated efforts of countries from around the world. In all, the complete destruction of one of mankind’s oldest and cruelest enemies cost roughly $100 million. It was a good deal.

Smallpox was the first disease fought on a global scale—but not the last. Other diseases are being combated in similar ways. Dracunculiasis, measles, and taeniasis, among many others, are being pushed toward total eradication. It’s safe to say that we’re all rooting for this list entry to be out-of-date as soon as possible.

7 Visiting The Solar System’s Two Ice Giants

The only man-made object ever to have gone to either Uranus or Neptune was the Voyager 2 spacecraft. During its flyby of Uranus, Voyager 2 came within 81,400 kilometers (50,600 mi). With just 5.5 hours to study the giant, it found that Uranus’s atmosphere was 85 percent hydrogen and 15 percent helium, that there was a boiling ocean 800 kilometers (500 mi) below the planet’s clouds, that its magnetic field was surprisingly aligned toward its equator, and that the planet had 10 more moons than previously known.

Its flyby of Neptune produced just as many surprises, such as the existence of the Great Dark Spot and active geysers on Neptune’s moon, Triton. These unique visits account for much of what we know of these planets.

It would be fair to mention that Voyager 2’s sibling is no slouch (and a bonus item for this list). Voyager 1 is the first and only man-made object to reach interstellar space, which is where the Sun’s magnetic field and constant flow of material stop affecting things. In other words, it’s in the space between stars.

6 A Capture Of Warships By Cavalry

The winter of 1795 was so cold that a Dutch fleet anchored near the island of Texel was frozen in the water during the French Revolutionary War. This allowed the French, under the command of Louis Lahure, to assault the warships on horseback. The result was 14 ships captured.

There is some dispute over how much of a battle actually took place. The Dutch report states that it was less of a battle and more of a discussion to comply with French orders, not to set sail, and to maintain military discipline. One Dutch surgeon aboard a captured ship reported quite calmly, “On Saturday morning, my servant informed me that a French hussar stood near our ship. I looked out my porthole, and indeed, there stood an hussar.”

Lahure later reported on the attack:

When the ships saw us, they prepared their defenses. I sent some tirailleurs ahead, and followed with the rest of my forces. The fleet was taken. The sailors received us [willingly] on board . . . This is the true story of the capture of the Dutch fleet, devised and executed by a 23 year old Chef de Bataillion.

French naval painters have portrayed the incident as a glorious battle, and that is how it is often remembered. Battle or not, the fleet was taken by the French in the one and only recorded capture of warships by cavalry.

5 The New Hebrides Trench

We may feel that there are few places left unexplored on Earth, but there are notable exceptions on the ocean floor. Our oceans are home to some 30 deep sea trenches, and as a species, we’re only just beginning to explore their mysteries. One example is the New Hebrides Trench, a 7,200-meter (23,600 ft) underwater gash that sits about 1,600 kilometers (1,000 mi) north of New Zealand, which has been visited only once by an unmanned lander.

The expedition in late 2013 found that not all deep sea trenches are alike. Creatures such as grenadiers, which are readily found in other trenches, were completely absent in New Hebrides. On the other hand, the usually rare cusk eel teemed in this particular trench. On our own planet, there still are places we’ve only seen once, let alone ever visited in person.

4 A Human Completely Cured Of HIV

Around 35 million people have died due to human immunodeficiency virus (HIV), and 1.1 million died in 2015 alone. With an estimated 36.7 million people living with the disease, it may seem surprising that only one human has ever been completely cured of it: Timothy Brown. This was accomplished by a bone marrow transplant from a donor with a genetic mutation that makes immune cells resistant to HIV infection.

Mr. Brown has remained cured of HIV since his treatments in 2007 and 2008. Because of the nature of his cure, it is very difficult to replicate Mr. Brown’s success, but doctors and scientists are still hunting for a way to remove this accomplishment from our list with gene therapy and other similar methods.

3 A Dry Niagara Falls

Though usually flowing at a rate of roughly 567,800 liters (150,000 gal) a second, the American Falls and the Bridal Veil Falls ran dry for several months in 1969. These are two of the three waterfalls that make up Niagara Falls, the third being the Horseshoe Falls. Their drying was to accommodate repair and preservation of the famous landmark.

Unsurprisingly, this lead to an increase in tourism. 89,790 people were recorded visiting in just one weekend. Some of those were even able to walk the dry riverbed, despite police warnings that doing so was dangerous.

The work was eventually complete, and the waters were released. Many hoped for an enormous wave of rushing water, but instead, the waters were released gradually until the flow returned to normal. It has stayed so ever since, but there has been some recent talk of drying the falls again for bridge repair and removing it from our list.

2 A Hurricane In The South Atlantic

Large storms are a common enough occurrence in the North Atlantic, with an average of 12 tropical storms and six hurricanes per season, but since 1974, only nine tropical storms have been observed in the South Atlantic. The reasons for this are a lack of preexisting disturbances and a commonly high vertical wind sheer, which disrupts the formation of these powerful storms.

Still, one of those rare South Atlantic tropical storms eventually developed into a hurricane: Cyclone Catarina. It made landfall as a Category 1 hurricane in March 2004, the only hurricane ever recorded in the South Atlantic. Named unofficially by Brazilian meteorologists, this hurricane reached wind speeds of 127 kilometers per hour (85 mph), damaged 36,000 homes, and killed at least three people.

1 A Flood Of Beer

The Horse Shoe Brewery, at the corner of Great Russell Street and Tottenham Court Road in St Giles, London, owned an incredible, 6.7-meter-high (22 ft) fermentation tank. This tank was in the process of brewing a brown porter ale on October 17, 1814, when one of the iron rings holding the structure together snapped. An hour later, the entire fermentation tank burst, releasing more than 1.2 million liters (320,000 gal) of fermenting beer.

In all, eight people died in the event itself, with another nine opportunists perishing some days afterward from alcohol poisoning. The brewery was taken to court on account of the unique flood, but the entire incident was ruled an act of God, and no one was held responsible. We may never see another flood like it, but you can commemorate the event every year at The Holborn Whippet, a local pub that brews a special anniversary ale to remember the one and only London Beer Flood.

Virus. The word is usually met with fear and understandably so. These microscopic collections of biological chemicals have been responsible for countless cases of death and sickness. The very mention of a deadly viral pandemic can send entire neighborhoods, cities, or even geographic zones into a state of sheer, frenzied panic.

Viruses are invisible to the naked eye, and they exist almost everywhere on Earth. They can infect fungi, plants, animals, and yes, humans. Some people have even speculated that viruses could pose a grave threat to the future of humanity.

However, not all viruses are bad. In fact, as we learn more about them, we are discovering that some viruses are actually quite beneficial. They have helped us in ways that we didn’t realize at first, and others pose interesting but positive possibilities for our future.

10 Bacteriophages

Bacteriophages are viruses that infect bacteria. They are found almost everywhere—in soil, in water, and even in the human body (mostly in our gut and mucus).

They were originally discovered in 1915 by Frederick Twort and have since become relatively famous in the field of microbiology as a therapeutic tool to help control bacterial infections.

While “phage therapy” is still under development, it is possible that it could be used in several different applications. It has already been used to treat some different types of ailments, and it shows great promise for the treatment of conditions ranging from cystic fibrosis to cancer. Some say that phage therapy also offers a viable replacement for traditional antibiotics in our age of antibiotic-resistant bacteria.^[1]

9 There Is a Virus That Gives Plants Extreme Heat Resistance

Tropical panic grass has always had the ability to grow in soil with an unusually high temperature. Researchers have since discovered that the cause behind this unique ability seems to be a virus. A fungal endophyte grows on this grass, and a virus that infects this fungus seems to be the source of this heat-resistant power.

Even more interesting, scientists attached the virus to other plants, giving them the same ability. The researchers even managed to grow tomatoes in soil as hot as 60 degrees Celsius (140 °F) without killing them.^[2]

But what happens if you remove the virus? They discovered that plants “cured” of the virus lost the ability to grow in extreme heat. Maybe that’s how the Human Torch does it.

8 Oncolytic Virus

Cancer—a word that causes dread in nearly every person affected by this potentially life-threatening disease. Doctors have sought different treatments and cures for the disease for more than 100 years; however, new interest has shifted focus to using viruses to treat cancer. And in recent years, a small but growing number of patients have begun to benefit from this approach. Research has shown that some viruses can infect and kill tumor cells. These viruses are known as oncolytic viruses and include viruses found in nature and viruses modified in the laboratory to reproduce efficiently in cancer cells without harming healthy cells.

Oncolytic viruses have long been viewed as tools for directly killing cancer cells. But a growing body of research suggests that some oncolytic viruses may work—at least in part—by triggering an immune response in the body against the cancer. When a virus infects a tumor cell, the virus makes copies of itself until the cell bursts. The dying cancer cell releases materials, such as tumor antigens, that allow the cancer to be recognized or “seen” by the immune system. For this reason, some researchers consider oncolytic viruses to be a form of immunotherapy—a treatment that harnesses the immune system against cancer.^[3]

7 Adenoviruses

Adenoviruses are a group of fairly common viruses. They are extremely contagious, usually cause only mild symptoms, and generally go away within a few days.

Some of them are actually quite well known. Bronchitis, pneumonia, many stomach infections, colds, croup, and even meningitis can all be found within the adenovirus family.

But researchers have also learned that one particular strain of the virus, type 52 (HAdV-52), binds to a particular type of carbohydrate found in cancer cells. This creates some interesting possibilities for virus-based cancer therapy.

There is obviously more studying to be done. But in the future, scientists might be able to arm viruses with genes to help fight cancer. They may also be able to use viruses to activate the body’s own immune system to fight the cancer itself.^[4]

6 Norovirus

Virologists have become especially interested in noroviruses. These particular micro life-forms are well known for their ability to cause epidemics of diarrhea on cruise ships. They are also infamous for their ability to ravage laboratory mice colonies with the disease.

But as it turns out, some strains of the virus have proven useful—especially for their role in helping to “normalize” mice that have grown in sterile environments. These mice don’t make enough T cells, which hurts their gut bacteria and immune response.

To fix the problem, researchers have shown that giving bacteria to the mice can help to rebalance their immune cells, but adding a norovirus to the mix can actually solve the same problem. Researchers also found that some norovirus strains helped lessen the effects of pathogens that usually cause weight loss, diarrhea, and other related symptoms in mice.

This makes for an exciting discovery as researchers unveil new ways to use viruses for good. Giving strains of the norovirus to humans to treat other diseases would be seen as highly controversial, but much evidence says that it could actually help.^[5]

5 Ancient Retroviruses

Ancient retroviruses may be the reason we don’t lay eggs.

Scientists have yet to unravel the entire part that ancient retroviruses have played in human development. But some of them, technically referred to as “endogenous retroviruses,” are believed to have helped in the evolution of the placenta in mammals.

To put it in super simple terms, some scientists believe that a primitive human ancestor contracted an endogenous retrovirus that caused mutations in the genetic code. This eventually led to mammals being capable of live birth.^[6]

The formation of the placenta was a huge step in the evolutionary process because it allowed mammals to give birth to live young. But when you take a really close look at the relationship between a mother and a fetus, it is not surprising that it shares many of the same characteristics you would expect to see in the relationship between a host and a parasite.

The work is ongoing. But don’t be surprised if we discover someday that the reason human females give birth to live babies instead of laying eggs is thanks to an ancient virus that altered our DNA.

4 Gamma-herpesviruses

This one is fairly technical, but it is no less amazing.

The Gammaherpesvirinae is technically a subfamily of herpesviruses that includes several different viruses. There are actually many different types of herpes viruses, with the best-known examples probably being herpes simplex virus type 1 and herpes simplex virus type 2, which cause cold sores and genital herpes.

As it turns out, latent infection with one type of gammaherpesvirus (type MHV-68) has been shown to increase resistance to infection with Listeria monocytogenes—the bacteria best known for food poisoning.

Who would have thought that herpes would help to fight food poisoning?^[7]

3 Cowpox

This story actually begins with a dangerous virus called smallpox. Nobody is sure where it came from. But it is believed that even as early as the third century BC, it was afflicting the Egyptian empire. Records of it have been discovered in China from the fourth century, and it has basically shown up everywhere since.

It was a devastating disease that killed about 30 percent of infected people. Even those who survived were often left with terrible scars as a result of the ordeal.

But in 1796, an English doctor named Edward Jenner made a discovery. He noticed that milkmaids tended not to contract smallpox as often as everyone else. Soon, he realized that a similar virus called cowpox often spread from cows to the milkmaids and may have had something to do with it.

He tested his theory by inoculating a boy with material from a cowpox sore and exposing him to smallpox. Although it may sound like a shocking experiment, it was actually successful. This led to the practice of vaccination that ended up eradicating the smallpox virus two centuries later.^[8]

2 GBV-C

HIV is probably one of the most terrifying and infamous viruses of the 21st century. Nevertheless, another virus, GBV-C, has been getting some attention from scientists for its effect on those who are HIV positive.

GBV-C is a member of the Flaviviridae family of viruses and can also be referred to as hepatitis G. The interesting aspect of this virus is its effect on the progression of HIV.

To put it simply, people who have both HIV and GBV-C tend to display a slower progression to AIDS and improved odds of survival—which is pretty amazing.^[9]

Who would have imagined that the existence of another virus could possibly slow down a virus as dangerous as HIV?

1 The Arc Gene

Did you know that human consciousness may have originally been caused by a virus? Yes, it is possible, and here is why.

Researchers believe that a virus attached itself to the genome of one of our ancestors long ago—probably even before we walked on two legs. But they also believe that a tiny bit of the genetic coding contained within the virus still exists within our brains today and may be responsible for some serious “brainpower,” including consciousness itself.

The Arc gene is essential for the learning process in humans. Weirdly enough, it communicates by sending genetic material from one neuron to another using a process that is commonly seen in viruses.^[10]

Further research must be done to determine exactly what this means. But right now, it looks as though it is very possible that we inherited our ability to learn and form conscious thoughts from the genetic material of some ancient brain virus!

Yes, the universe is definitely a weird and mysterious place.

Joshua Sigafus is just a writer who is trying to make the world a better place.