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(This program is no longer streaming). Sixty-six million years ago, an asteroid wiped out the dinosaurs in a fiery global catastrophe. But we know little about how their successors, the mammals, recovered and took over the world. Now, hidden inside ordinary-looking rocks, an astonishing trove of fossils reveals a dramatic new picture of how rat-sized creatures ballooned in size and began to evolve into the vast array of species—from cheetahs to bats to whales to humans—that rule our planet today.

Amazing fossils reveal how mammals took over after an asteroid wiped out the dinosaurs.

Rise of the Mammals

From singing whales and squeaking bats to thumping spiders and clicking dolphins, the world is filled with the exotic sounds of our fellow creatures. What are they saying? While we believe language sets us apart, some animals demonstrate they can learn our language—like Chaser the dog, who recognizes hundreds of words, and Kanzi the bonobo, who appears to have a sophisticated understanding of spoken English. But can we decode their own communications? NOVA Wonders follows researchers around the globe who are deciphering an amazing array of clues that reveal how animals share information critical to their survival. Will we one day be able to write the bat dictionary or decode the hidden sign language of chimps? And what can these findings tell us about the roots of our own language?

Can we crack the code of animal communication?

What Are Animals Saying?

(This program is no longer available for online streaming.) A seven-mile-wide asteroid collided with Earth 66 million years ago, triggering a chain of events that coincide with the end of the dinosaurs. But experts have long debated exactly what happened when the asteroid struck and how the giant beasts met their end. Now, scientists have uncovered compelling new clues about the catastrophe—from New Jersey to the wilds of Patagonia—and an international expedition of scientists has drilled into the impact crater off the coast of Mexico, recovering crucial direct evidence of the searing energy and giant tsunami unleashed by the asteroid. Join NOVA as scientists piece together a chillingly precise unfolding of the Earth’s biggest cataclysm, moment by moment, and discover how our early mammalian ancestors managed to survive and repopulate the Earth. (Premiered December 27, 2017)

Experts drill into the impact crater of an asteroid that created a worldwide cataclysm.

Day the Dinosaurs Died

The Surprising Power of a Bird Brain

Bird brains may be tiny, but they pack in as many—or more—neurons as much larger animals.
Similar to humans and other animals with higher intelligence, the executive center of a bird&#x27;s brain allows them to strategize and organize ideas.
The Surprising Power of a Bird BrainPublished: August 28, 2025NARRATOR: Compared to other birds, parrots and crows have large brains in relation to their body size. And scientists believe that may be one reason why they can work out solutions to problems they don&#x27;t encounter in the wild. Most bird brains are small, but they have one critical area in common with humans and other animals with higher intelligence.JOHN MARZLUFF: The executive center of the bird&#x27;s brain really allows them to make plans and strategies and organize ideas.NARRATOR: Bird brains may be tiny, but for their size they seem to contain more brain cells or neurons than many other animals.JOHN MARZLUFF: The number of neurons is a better indication of brain power than the physical size of the brain. And this is an interesting thing we&#x27;ve learned recently that bird brains actually pack a lot more neurons into a particular area than do mammal brains. So even though they&#x27;re physically very small in size, they have a lot of punch in that size.

Bird brains may be tiny, but they pack in as many—or more—neurons as much larger animals.

These Birds Are Smarter Than You Think

Can these birds solve the puzzle and claim their prize?
When birds crack a puzzle in more than one way, they’re showing the kind of flexible problem-solving once thought uniquely human. Could intelligence be more widespread in nature than we realized?
These Birds Are Smarter Than You ThinkPublished: August 19, 2025NARRATOR: This experiment is designed to compare how New Caledonian crows and kea solve problems. Wek represents the crows, and for the kea parrots, this is Kermit. Their reward: a peanut. Their challenge is called a multi-access box. The first time both birds see the puzzle, they make the same choice. They just pull the string. Then the researchers take that solution away to see what they&#x27;ll do next. Wek uses the stick to poke the nut free, but this isn&#x27;t a surprise.AUGUSTE VON BAYERN: New Caledonian crows are very special because they&#x27;re the only crow species that use tools in the wild. They obtain a lot of their diet by using tools.NARRATOR: Kea parrots don&#x27;t use tools in the wild, but Kermit figures out a solution with the ball and chute. Again, the researchers remove the option that&#x27;s been used. For Wek, the hole for the stick is taped over. Wek has to try something else, so she tries the ball and chute. With two choices left, Kermit just opens the door, reaches inside, and takes the peanut. But Wek won&#x27;t take this approach.JOHN MARZLUFF: The last thing a crow wants to ever do is stick its head in something. They&#x27;re extremely vulnerable if they do that and to stick their head inside that box, it could trap them in it.NARRATOR: Wek still opens the door, but rather than put her head inside, she pokes the nut free with a stick. Kermit&#x27;s last option is the stick. His curved beak makes it very hard to hold, but he still sees this as a potential solution, even though it&#x27;s not easy. Both birds found four different solutions to the puzzle, showing they&#x27;re able to think flexibly.

Can these birds solve the puzzle and claim their prize?

The Next Big Earthquake Could Sink Parts of the Pacific Northwest

A massive earthquake along the Cascadia Subduction Zone could unleash a tsunami and sink parts of the Pacific Northwest by several feet.
A 2025 study suggests that when the next &quot;Big One&quot; hits, coastal land could sink by up to 6 feet. That sudden drop could instantly double the number of people, homes, and roads exposed to flooding.
The Next Big Earthquake Could Sink Parts of the Pacific NorthwestPublished: August 4, 2025NARRATOR: In this region, a massive earthquake is pretty much inevitable. This is the Cascadia Subduction Zone. It&#x27;s one of the top hazards on the planet. Here, the ocean floor is slowly diving under North America. Massive earthquakes are expected here every 500 years or so, and the last one was in 1700.WENDY BOHON: So it&#x27;s not a matter of if, it&#x27;s just a matter of when.NARRATOR: A 2025 study suggests that the quake could suddenly sink part of the Pacific Northwest and climate driven sea level rise would only make it worse. So why is the Cascadia Subduction Zone so dangerous and when will the next big one happen? The Cascadia Subduction Zone is a major fault line that spans Vancouver Island in Canada to Northern California, but it&#x27;s not really a line at all. It&#x27;s a crack where two massive tectonic plates meet. It&#x27;s where one of the largest earthquakes in the history of North America happened more than 325 years ago. in January of 1700. The earthquake had an estimated magnitude of nine, and it caused a tsunami. A graveyard of trees that fell victim to flooding are still in the area. The subduction zone has been pretty quiet ever since. The last magnitude nine earthquake on Earth was caused by a subduction zone known as the Japan Trench in 2011. It spurred a tsunami and caused widespread devastation, including a nuclear disaster at the Fukushima Daiichi power plant. Subduction zones produce the biggest earthquakes in the world. They happen where one tectonic plate is sliding down another plate.WENDY BOHON: In Cascadia, you have one plate diving down beneath another. This section gets locked and it pushes this part up. When the fault ruptures, when the amount of stress overcomes the friction, it bounces back, which lifts up the water above it and causes that water to flow out in all directions. And that water flowing out in all directions is the tsunami.NARRATOR: The inevitable earthquake in the Pacific Northwest is what&#x27;s called &quot;the big one,&quot; and it would absolutely be devastating to a number of coastal communities. But the Cascadia Subduction Zone is not actually one continuous fault line. It has ruptures in it that form at least four major segments. It&#x27;s possible that an earthquake in one zone might not trigger an earthquake in the others, but the longer the segment, the bigger the quake. One segment runs from Vancouver Island to the Oregon border. Some scientists think that this is the most dangerous section and could spark the biggest earthquakes. So when will this happen? Unfortunately, earthquakes often happen without any clear warning signs, and scientists haven&#x27;t yet identified reliable predictors. The United States Geological Survey even says that, &quot;Neither the USGS nor any other scientists have ever predicted a major earthquake,&quot; and that they do not expect to know how to predict earthquakes in the foreseeable future. Whoa. Even if scientists can&#x27;t predict when an earthquake will strike, they can use analytical models to study the potential effects. Some researchers found that if the Cascadia earthquake were to strike today, the coastline could suddenly sink by up to six feet raising the sea level. And more than doubling the number of people, buildings, and roads currently exposed to coastal flooding risks. Sea levels are already rising across the globe. But the Pacific Northwest coast has seen much slower rise than other parts of the US coastline because of the subduction zone. It&#x27;s slowly pushing the coastline up almost as fast as the sea level is rising in some areas. But a massive earthquake could quickly reverse that. According to one projection, by the year 2100 sea levels along the Pacific Northwest could rise by almost three feet. Combined with a Cascadia quake, that&#x27;s a sea level difference of nearly nine feet compared to today. And don&#x27;t forget that when the earthquake strikes, it will trigger a tsunami, which could bring waves over 50 feet high in some locations. For now, some communities are taking action against these deadly threats by creating high ground. A tsunami could come only 15 minutes after an earthquake, and experts say it&#x27;s imperative to get to high ground ASAP. The thing is that in many low lying coastal communities, that isn&#x27;t an option. So vertical evacuation structures like towers and platforms where people can get to high ground without traveling, great distances are essential. Right now, there are three vertical evacuation towers in the Pacific Northwest, a tsunami evacuation tower built by the Shoalwater Bay Indian Tribe, an elementary school gym that was rebuilt with a fortified foundation to withstand massive earthquakes and a new roof built to hold more than a thousand people, and an Oregon State University marine sciences building. There are more vertical evacuation structures planned for the Pacific Northwest, but one study found that many more are needed. The trouble is we don&#x27;t know how much time we have until the next big one.

A massive earthquake along the Cascadia Subduction Zone could unleash a tsunami and sink parts of the Pacific Northwest by several feet.

Can Birds Recognize Faces?

Crows remembered the face of a person they considered a threat—even across generations.
Researchers caught, tagged, and released crows to see if they can recognize the face of a person who’s a threat. They discovered the crows were warning each other that the person in the mask was dangerous — even generations after it the initial capture.
Can Birds Recognize Faces?Published: July 30, 2025NARRATOR: John Marzluff went undercover to test the birds&#x27; reactions to being caught and tagged.JOHN MARZLUFF: When we first captured birds, we were wearing this mask, so the birds that were immobile under a net saw this person coming to them, grabbing them, stretching their wings out to measure them, applying rings to their legs to identify them, and then letting them go.NARRATOR: Crows don&#x27;t like being caught, even when they&#x27;re unharmed, so the question was: would they remember that the masked man was a threat? A few days after the initial tagging, Marzluff walked across the campus again. He kept the mask on, but he left the crows alone to see if he&#x27;d get any response.JOHN MARZLUFF: It was very striking. The first time after we did this experiment and we walked with the caveman mask, birds immediately responded to that. They scolded with harsh calls that are indicative of a predator, and they gathered around us. They attracted others in and they would even dive down at us.NARRATOR: Marzluff discovered that the crows were somehow telling each other that the person in the caveman mask was dangerous. And what&#x27;s more amazing, even though the team never again caught crows with the mask on, that reaction has been passed down through several generations.JOHN MARZLUFF: It&#x27;s been 11 years since we caught seven birds on our campus with this mask, and nearly half of all the birds we encounter on a given day respond strongly to that face, even though they weren&#x27;t even born at the time we first did our capture, the only experience they have with that caveman is hearsay.

Crows remembered the face of a person they considered a threat—even across generations.

Why Are There Stone Tree Trunks in the Arctic?

Fifty-million years ago these rocks were trees and this Arctic tundra was a steamy swap.
Ellesmere Island, high in the Canadian Arctic, is only 800 miles from the North Pole. 50-million years ago, the treeless hillside would have been completely different.
Why Are There Stone Tree Trunks in the Arctic?Published: July 7, 2025KIRK JOHNSON: This frozen tundra may look barren, but for me as a paleobotanist, this is geologic heaven. There are a few small arctic wildflowers and some scrappy ground cover, but the nearest living tree is a thousand miles south of here. Finally, we reach what I&#x27;ve been looking for.Wow. Oh my God, there are some amazing stumps here. Look at this.Sticking out of the hillside are a bunch of weird brown rocks. These are petrified tree stumps. Geologists have dated these trees to around 50 million years ago. Back then, this treeless hillside would have been completely different.There&#x27;s a lot of clues here to how this forest got to be the way it is. The first is that all these stone trunks are surrounded by coal, black rock, which is a very strong signal that these trees when they were growing were growing in a swamp. The second clue are these radiating roots. In swamps, roots grow out and not down.But what kind of trees were these?These rocks are just chunky silt stones that are quite near the petrified forest, and I&#x27;m breaking them apart because I&#x27;m looking for Fossil leaves. If I can find the leaves that go with those trees, I can put that forest back together again. Come to papa.Now, here we go. You see through the close-up of that thing?KIRK JOHNSON: What have you got?KIRK JOHNSON: This is Metasequoia, little needles. It&#x27;s the dawn redwood. It&#x27;s this Conifer, and these whole sprigs will fall off as they&#x27;ve done here and land in the mud. This used to be mud. Now, it&#x27;s a rock. That would go with those trunks, the petrified forest.Together, these leaves and tree trunks give us a window into the past. 50 million years ago, this dried, barren tundra was a warm, humid swamp covered with lotus plants, ferns, and Metasequoia trees that were as tall as 150 feet. The area covered in ice today was once a massive forest that stretched all the way up to the edge of the Arctic Ocean. Water ran off the land forming a surface layer of freshwater. Instead of sea ice, the North Pole was covered in subtropical floating ferns.

Fifty-million years ago these rocks were trees and this Arctic tundra was a steamy swap.

Can Lemurs Count?

Researchers designed a test to see how well lemurs can compare quantities.
If he chooses correctly, he wins a sugar pellet. But researchers have to ensure Teres is paying attention to number and not something else.
Can Lemurs Count?Published: May 6, 2025Narrator: Like all primates, lemurs are related to humans through a common ancestor that lived as many as 65 million years ago. Scientists believe lemurs share many characteristics with those earliest primates, making them a window, though a blurry one, into our ancient past.Liz Brennan: Got a choice here, Teres. Come on up.Narrator: Duke professor Liz Brennan investigates how well lemurs, like Teres here, can compare quantities.Liz Brennan: We need to figure out whether they can really use number, pure number, as a cue.Narrator: To test how well Teres can distinguish quantities, he&#x27;s been taught a touchscreen computer game. The red square starts a round. If he touches it, two squares appear containing different numbers of objects. He&#x27;s been trained that if he chooses the box with the fewest number, he&#x27;ll get a reward, a sugar pellet. A wrong answer?Liz Brennan: We have to do a lot to ensure that they&#x27;re really attending to number and not something else.Narrator: To make sure the test animal is reacting to the number of objects and not some other cue, Liz varies the object, size, color, and shape. She has conducted thousands of trials and shown that lemurs and rhesus monkeys can learn to pick the right answer.Liz Brennan: Teres obviously doesn&#x27;t have language, and he doesn&#x27;t have any symbols for number. So is he counting? Is he doing what a human child does when they recite the numbers one, two, three? No. And yet, what he seems to be attending to is the very abstract essence of what a number is.

Researchers designed a test to see how well lemurs can compare quantities.

Why Just Planting Trees Won’t Save the Planet

Could restoring lost forests help slow climate change?
A paper published in 2019, estimated that there is enough land on Earth to support an extra trillion trees to capture carbon. But in the rush to grow trees, people ignored the supporting environment that exists in a forest. Discover why biodiversity matters in forests.
Why Just Planting Trees Won’t Save the PlanetPublished: April 17, 2025Narrator: Could restoring lost forests absorb enough carbon to help slow climate change? To find out, Tom and a team built a computer model to estimate the potential.Tom Crowther: So we collect data from all over the planet, and that can show us there&#x27;s about 0.9 billion hectares of land outside of urban and agricultural land where forests might naturally be able to regenerate. That&#x27;s a big chunk of land that would be able to capture a staggering amount of carbon.Narrator: Calculation suggested that to capture this carbon, there was enough land to support an extra trillion trees, a seductive idea that made headlines around the world.Tom Crowther: It just went viral beyond anything I could have been prepared for. And I think that alliteration, trillion trees, was both a blessing and a curse. In one way, it captured everyone&#x27;s imagination. &quot;Great, we bring back a trillion trees and we&#x27;re gonna be flying.&quot; But the downside was everybody thought that meant planting trees. Somehow it wasn&#x27;t about the forest, it was about the trees, and that is where things started to go wrong.It nearly finished all of our careers. Companies and governments were under a lot of pressure to limit their emissions. They saw this as a chance to just bang a load of trees in the ground, and then they don&#x27;t need to cut emissions. The projects denounced as a result of our paper saying, &quot;Don&#x27;t worry, we&#x27;re gonna buy up land and we&#x27;re gonna plant trees.&quot;Narrator: In the rush to grow trees, people ignored the supporting environment that exists in a forest.Robin Wall Kimmerer: There are places on the planet where biodiversity continues to thrive, and those places are by and large in indigenous homelands. Biodiversity is the sum total of all of the organisms that are here, and you think, well, why does it matter?In a forest which is self generating, you get all the different forms of trees and the understory and the mosses and the fungi and the birds all in relationship. It&#x27;s this beautiful web that doesn&#x27;t really exist in a monocultural plantation.Narrator: When Tom&#x27;s paper was published, many quite literally couldn&#x27;t see the forest for the trees. By planting rows of single tree species to capture carbon instead of reducing carbon emissions.Tom Crowther: This greenwashing is one of the most insidious threats to climate change and biodiversity. And through this paper, in some people&#x27;s minds, I become synonymous with greenwashing. I still regret how I handled that paper. It&#x27;s the hardest thing to be hated by people that you agree with.

Could restoring lost forests help slow climate change?

Topic: Nature

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