Science is an ongoing process, which means new discoveries often upend old theories.
Contrary to what many people learned in school, Pluto is not a planet (well, sort of), dinosaurs didn't look like the pictures in your textbook, and atoms aren't the most basic components of matter.
Here are some science "facts" you may have learned in school that aren't true.
Visit Business Insider's homepage for more stories.
If you were to file into a classroom and open your notebook for science class today, the subject matter might be a little different from when you were in school.
Our body of scientific knowledge is constantly growing and changing. New discoveries or studies often lead to changes in old theories and sometimes even invalidate them altogether. That means some of the "facts" you learned in school aren't necessarily true anymore.
For example, dinosaurs probably didn't look the way your textbook depicted them. The origins of Homo sapiens aren't as neat as the timeline you might have learned. And many of the nutrition and exercise guidance from your health classes has been debunked.
Here are some science facts you may have learned in school that aren't true anymore.SEE ALSO: 9 things that aren't helping the environment as much as you think they are, from recycling to carbon offsets
Myth: We don't know what caused the dinosaurs' mass extinction.
Scientists used to scratch their heads about what caused the extinction that ended the age of dinosaurs — theories ranged from low dino sex drives to a world overrun by caterpillars.
But in 1978, geophysicists stumbled upon Chicxulub, a crater in the Yucatan Peninsula made by the 6-mile-wide asteroid that likely triggered the dinosaurs' demise.
Since that discovery, researchers have uncovered more details about the asteroid's impact. The collision caused a mile-high tsunami, sparked wildfires, and released billions of tons of sulfur into the atmosphere, blotting out the sun for years.
This year, new climate modeling laid a popular competing theory about the dinosaurs' extinction to rest.
Many scientists had previously suggested that eruptions of a giant range of volcanoes in modern-day India — called the Deccan traps — contributed to the dinosaurs' downfall. The sulfur gases they released were thought to have rapidly cooled the climate, much like the asteroid's global dust cloud.
But recent climate-modeling research found that those eruptions weren't a big factor. A January study found that the major temperature changes at the time only aligned with the asteroid impact.
"It was the asteroid 'wot done it," Paul Wilson, a paleoclimatologist who co-authored that paper, told the BBC.
Another study found that the Deccan volcano eruptions may have actually helped re-warm the climate after the asteroid hit.
Myth: Dinosaurs were scaly, earthy-colored lizards.
Dinosaurs likely had feathers.
Feathers are rarely preserved in the fossil record, but scientists have uncovered feathered dino fossils in China and Siberia, suggesting plumage was common across the great lizards.
"Probably that means the common ancestor of all dinosaurs had feathers," Pascal Godefroit, a paleontologist who wrote a 2014 study on a key Siberian fossil, told National Geographic.
Underneath the feathers, dinos could have had brightly colored scales, like many modern-day lizards.
Feathers have never been found on a T. rex specimen, but fossils of other tyrannosaur species do have preserved feathers. So paleontologists can assume the T. rex had them too.
Though adult T. rexes were mostly covered in scales, scientists think they had patches of feathers on attention-getting areas like the head and tail.
Myth: The T. rex was a running, roaring lizard like the one you saw in "Jurassic Park."
Though a terrifying predator, the "king of the dinosaurs" probably did not roar or sprint.
The dinosaur's long stride could carry it as fast as 25 mph, but it never reached a suspended gait, since it always had at least one leg on the ground.
A 2016 study suggested that instead of roaring, the T. rex probably cooed, hooted, and made deep-throated booming sounds like the modern-day emu.
Myth: Dinosaurs laid eggs with hard shells.
Early dinosaurs may have laid leathery, soft-shelled eggs, like turtles do today. Paleontologists recently found fossils of such eggs from two dinosaur species in the Gobi Desert.
Myth: Neanderthals were dumb brutes who didn't mingle with Homo sapiens.
Evidence of Neanderthal cave art in Europe significantly predates similar paintings by Homo sapiens.
Our extinct cousins also crafted tools and ornaments out of stone and bone, made tar glue from birch bark that allowed them to attach wooden handles to stone tools, and cooked with fire (though they may have relied on lightning strikes to start the flames).
Perhaps this intelligence is what inspired early humans to breed with Neanderthals and Denisovans, another early hominin species.
Myth: Homo sapiens first emerged 200,000 years ago in east Africa.
Groups of Homo sapiens may have evolved at the same time all over Africa instead of in one primary location, a 2018 paper suggested. A skull discovered in 2017 also showed that was happening about 300,000 years ago, further back in history than previously thought.
Not all of these groups would have looked identical, but they may have been close enough to all be considered Homo sapiens. The groups would have interacted with one another and migrated across the continent.
So instead of emerging in one area in eastern or southern Africa and then spreading from there, distantly related groups of humans across the continent could have become more similar over time.
Read more: A handful of recent discoveries has transformed our entire understanding of human history
Myth: Humans first reached North America 13,000 years ago by crossing the Bering land bridge.
Archaeologists have discovered evidence of much earlier human presence. Most recently, they uncovered nearly 2,000 stone tools, ash, and other human artifacts in a high-altitude cave in Mexico, some of which date back 30,000 years.
Scientists have also found fossilized human poop that's about 14,000 years old in an Oregon cave. Artifacts from a settlement in southern Chile were dated to between 14,500 and 19,000 years old. And a horse jaw bone that bore human markings suggested humans occupied the Bluefish Caves of Yukon, Canada 24,000 years ago.
But none of these discoveries pushed the timeline as far back as the Mexican cave artifacts.
The evidence from the cave suggests humans lived in North America during the last Ice Age — long before the Bering land bridge existed.
Lorena Becerra-Valdivia, an archaeological scientist at the Universities of Oxford and New South Wales, told Business Insider that "the new findings suggest that humans likely took a coastal route."
That means they were probably seafarers who arrived by boat, possibly from modern-day Russia or Japan. Then they expanded south by sailing down the Pacific Coast.
Myth: Camels store water in their humps.
Camels humps store fat, which the animals burn for fuel when traveling long distances with limited resources. A camel can use that fat to replace about three weeks' worth of food, according to Animal Planet.
It's the camel's red blood cells that enable it to go a week without drinking water. Unlike other creatures, camels have oval-shaped blood cells that are more flexible and enable them to store large quantities of water.
Myth: Bats are blind.
Many bats rely on echolocation to navigate, but that doesn't mean they can't see.
Myth: The food pyramid is the gold standard of nutrition.
The US Department of Agriculture released the Food Guide Pyramid in 1992, but much of the nutritional advice it offered has since been debunked.
The pyramid made no distinction between refined carbs like white bread and whole grains like brown rice. There is also no distinction between the healthiest proteins (like beans, nuts, and fish) and red meat, which can increase one's risk of cancer and heart disease.
The chart also banished healthy fats to the "use sparingly" tip of the pyramid, lumping them in with added sugars and trans fats from processed oils and packaged foods. In the mid-1990s, Harvard researchers estimated that trans fats led to roughly 50,000 preventable deaths each year in the US. However, research has found that the healthy unsaturated fats found in foods like nuts, seeds, and avocados are crucial to a balanced diet.
Myth: Milk is good for your bones.
Much of the hype about milk comes from dairy industry marketing campaigns, though the USDA helped too. A page on the department's website tells us that adults should drink three cups of milk per day, mostly for calcium and vitamin D, and that kids should drink two to three cups to build strong bones.
However, multiple studies have found no association between drinking more milk (or taking calcium and vitamin D supplements) and experiencing fewer bone fractures. Some studies have even found an association between drinking milk and higher overall mortality; that doesn't mean milk consumption was the cause, but it's not an endorsement.
Another page on the USDA's website has changed the three-cup recommendation to encompass the entire dairy category, which includes yogurt and cheese.
Myth: Crunches and sit-ups are great for your core.
A lot of us practiced this move in gym class, but many experts have told Business Insider that crunches are not efficient core-builders and that they can damage your back and neck if you do them wrong.
The nonprofit American Council on Exercise says that when it comes to crunches, a lot of people "perform this movement too rapidly" and cheat by using their hip flexors.
"This technique tilts the pelvis anteriorly, increasing the stress on the low back, and should be avoided," the council says on its website.
Read more: Traditional sit-ups and crunches are terrible for you, according to personal trainers — here's what they suggest instead
Myth: Drinking alcohol kills your brain cells.
Alcohol can damage the connections between your brain cells, but it doesn't actually kill them.
Still, many studies have found that excessive drinking over long periods can damage the brain, and children with fetal alcohol syndrome often have fewer brain cells.
Studies have also found that heavy (and even moderate) drinkers can have increased brain shrinkage.
Myth: Diamonds come from coal.
Diamonds and coal are both made from carbon, but most of Earth's diamonds are much older than its coal.
Diamonds also form much deeper in the Earth's high-pressure mantle, via a process that has nothing to do with coal.
Coal, meanwhile, is found in Earth's crust.
Myth: There's a dark side of the moon.
There is a side of the moon that we never see from Earth, but it's not dark all the time.
The moon is tidally locked with Earth, which means that we are always looking at the same side of it. As Earth spins, and our cold rock satellite rotates around it, sunlight falls across all sides of the moon.
Myth: Pluto is the ninth planet. (Well, this one's complicated.)
The International Astronomical Union originally classified Pluto as the ninth planet that orbits the sun.
But in 2005, Eris, another really big space rock that orbits the sun, was discovered. It's 27% more massive than Pluto, though a 2015 finding later revealed Pluto to be slightly larger. That forced the IAU to rethink what a planet actually is.
The IAU decided on criteria that neither Pluto nor Eris met, so neither could be considered one of the major planets that orbits the sun. Instead, they're both dwarf planets.
So yes, Pluto is a planet — it's just a dwarf planet.
Myth: Mars is a desert of red dust with no water.
Three years' worth of radar data suggests that a lake of liquid water might lurk beneath Mars' polar ice caps, a study published last year said.
Previous findings also indicated that liquid water might flow seasonally across Mars' surface, though the discovery has been thrown into question.
Myth: Black holes are invisible.
In school, you may have learned that black holes swallow everything around them, including light. That's sort of true.
A black hole is an extremely compact, massive object with a powerful gravitational pull — so powerful that not even light can escape. But that reach only extends a few billion miles.
The dark center that swallows up light is called the event horizon, and it's usually surrounded by a glowing circle of dust, rock, and other space debris that is slowly falling towards it. This region of the black hole, called the accretion disk, produces plenty of visible light. That's how scientists got the first picture of a black hole last year.
Sometimes collisions or reactions within the accretion disk even produce explosions of bright light.
Myth: Nothing moves faster than light.
Light moves at 299,792,458 meters per second in a vacuum, but it slows down when it travels through various substances. For example, light moves at about 75% of that speed through water and about 41% of that speed through diamond.
Electrons, neutrons, or neutrinos can outpace photons of light in such media — though they have to bleed off energy as radiation when they do.
The expanding fabric of space also once exceeded light-speed during the Big Bang, and physicists think wormholes and quantum entanglement might defy the rule as well.
Read more: The speed of light is torturously slow, and these 3 simple animations by a scientist at NASA prove it
Myth: The phases of matter are liquid, solid, and gas (and maybe plasma).
This may not be elementary-school-science material, but there are many more states of matter, including quark-gluon plasma, superfluids, Bose-Einstein condensates, fermionic condensates, photonic matter, and possibly even supersolids — just to name a few.
Liquid, solid, and gas are just the states you can observe in everyday life.
Plasma, which some people learned about as the state of matter for lightning, is the most abundant form of matter in the universe.
Myth: Atoms, the building blocks of matter, can be broken down only into electrons, protons, and neutrons.
Matter gets much smaller and more complex than that. Quantum physics predicts 18 types of elementary particles, 16 of which have been detected by experiments.
Protons and neutrons are made up of quarks, which are held together by gluons.
Dave Mosher and Aylin Woodward contributed reporting to this post.
This article has been updated to include new information. It was originally published on September 19, 2019. An earlier version of this story incorrectly stated that Eris is larger than Pluto.