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It also allowed the establishment of the thermohaline circulation, a global water conveyor belt, which transports warm water across the Atlantic, and influences the climate of the East Coast of North America, the West Coast of Europe,and many other areas.It's a challenge to track all of the ways the collision of the Americas changed the world,but it's safe to say that the ripples of the Great American Biotic Interchange have propagated through the history of life on the planet, and that of mankind. What if these species hadn't gone extinct, or if there were no monkeys in Central America, or jaguars in South America? What if the thermohaline circulation wasn't flowing? Would the East Coast of North America be much colder? It all goes to show some of the most impactful transformations of our planet aren't the explosive ones that happen in an instant, but the ones that crawl towards irreversible change. We are the product of history.

Horses, llamas, tapirs, cougars, saber-toothed cats, gomphotheres, and later humans also headed south across the land bridge. But what happened on land is only half the story. What had been one giant ocean was now two, creating differences in temperature and salinity for the two bodies of water.The isthmus also became a barrier for many marine organisms, like mollusks, crustaceans, foraminifera, bryozoans, and fish, and separated the populations of many marine species.

From South America, mammals like ground sloths and glyptodonts were widly distributed in North America. Moreover, many South American tropical mammals, like monkeys and bats, colonized the forests of Central America, and are very abundant today. South American predator marsupials went extinct 3 million years ago,at which point North American predators, such as cats, bears and foxes, migrated south and occupied the ecological space left behind.

As these plates continued to surf the Earth's magma layer far beneath the Pacific Ocean floor, the Caribbean Plate migrated eastward,and about 15 million years ago, South America finally collided with this Central American Arc. This gradually closed the water connection between the Pacific and the Caribbean, creating a land bridge, which connected North America to South America. Terrestrial organisms could now cross between the two continents, and from the fossil records, it's evident that different waves of their dispersals took place. Even though plants don't physically move,they are easily dispersed by wind and waves, so they migrated first, along with a few species of birds. They were followed by some freshwater fishes and amphibians, and finally, various mammals began to traverse the bridge.

Our story begins 65 million years ago, the beginning of the age of mammals,when what is now North and South America were continents separated by a marine connection between the Pacific and Atlantic Oceans. During this time, South Americawas the home of fauna that included armored glyptodonts as large as compact cars,giant ground sloths weighing more than a ton, opossums, monkeys, and carnivorous terror birds. North America had its own species, such as horses, bears, and saber-toothed cats. Over 20 million years, the shifting of the Farallon and Caribbean Plates produced the Central America Volcanic Arc, a peninsula connected to North America, with only a very narrow seaway separating it from South America.

Tens of millions of years ago,a force of nature set two giant masses on an unavoidable collision course that would change the face of the Earth and spell life or death for thousands of species. The force of nature was plate tectonics, and the bodies were North and South America. And even though they were hurdling towards each other at an underwhelming 2.5 cm per year, their collision actually did have massive biological reprocussions by causing one of the greatest episodes of biological migration in Earth's history: The Great American Biotic Interchange.

Stars explode, mountains erode,and buildings, plants, and animals are all slowly but surely pulverized into fine grey powder.We’re all destined to become dust, but it’s also possible that we came from it.Interstellar dust has been found to carry organic compounds through space. It’s possible that billions of years ago, some of these cosmic particles were the seed of life on our little blue planet.

In addition to markers of humans, animals, and landscapes, dust also contains particles from further afield. When a star explodes in a distant galaxy, super hot gases vaporize everything nearby.Then, the dust settles; minerals condense out of the gas. Floating out there between planets and galaxies, this extraterrestrial dust contains tiny pieces of extinguished stars and the building blocks of future celestial bodies. Every year, tens of thousands of tons of cosmic dust lands on Earth and mingles with terrestrial minerals. This blend of chemicals, minerals, and intergalactic particles settles out of the air onto surfaces in our homes, mixing with the detritus of each house’s occupants.

In Spain, where the land is rich in carbonate materials, dust contains 20 times as much calcium as dust in Nigeria, where the geology is quite different. After a particularly violent storm,scientists identified dust from the Sahara Desert thousands of miles away in London,based on its specific composition. In the future, we may be able to pinpoint the origins of dust samples even more specifically, down to a particular neighborhood or even house something that may be of great help for forensic specialists.

Dust mites eat animal dander, human skin, and some fungi. We shed dead skin cells constantly, and wherever we live, they mix into the household dust. The same goes for our pets: their dander and hairs enter the mix, as do tiny pieces of thread and cotton fibers from our clothes. These components make every household’s dust a unique blend of bits from its particular inhabitants. Household dust also contains substances that blow in from the wider world. Depending on the local geology, finely ground quartz, coal, or volcanic ash might enter the air as atmospheric dust, along with pollen and fungal spores. Industrial activities also contribute cement powder, particles from car tires, and other chemicals to the airborne mix.The combination of these elements can be as unique as a fingerprint.

This realm is right under our noses, but from our perspective, the tiny specks of brilliant color blend together into a nondescript grey. What are these colorful microscopic particles? What distinguishes the dust in your house from, say, sand on a beach is that it is a mixture of many different ingredients. It can contain grains of sand, dead skin cells, tiny hairs and threads, animal dander, pollen, manmade pollutants, minerals from outer space, and, of course, dust mites.

Meet Dermatophagoides farinae. Crawling around on eight legs, this creature has no eyes to appreciate the kaleidoscope of colors around her. She relies on her extraordinary sense of smell to lead her to food and safe places to lay eggs. And she’s smaller than a pinhead. Dermatophagoides farinae is a dust mite. Less than a tenth the size of an ant,a dust mite’s whole world is contained in the dusty film under a bed or in a forgotten corner.

elephant attacks on human villages have usually occurred right after massive poachings or cullings, suggesting deliberate revenge. When we consider all this evidence, along with the fact that elephants are one of the few species who can recognize themselves in a mirror, it's hard to escape the conclusion that they are conscious, intelligent, and emotional beings. Unfortunately, humanity's treatment of elephants does not reflect this, as they continue to suffer from habitat destruction in Asia, ivory poaching in Africa, and mistreatment in captivity worldwide. Given what we now know about elephants and what they continue to teach us about animal intelligence, it is more important than ever to ensure that what the English poet John Donne described as nature's great masterpiece" does not vanish from the world's canvas.

But perhaps the most amazing thing about elephants is a capacity even more important than cleverness: their sense of empathy, altruism, and justice. Elephants are the only non-human animals to mourn their dead, performing burial rituals and returning to visit graves. They have shown concern for other species, as well. One working elephant refused to set a log down into a hole where a dog was sleeping, while elephants encountering injured humans have sometimes stood guard and gently comforted them with their trunk.

The cerebral cortex, on the other hand, enables problem solving, which elephants display in many creative ways. They also tackle problems cooperatively, sometimes even outwitting the researchers and manipulating their partners. And they've grasped basic arithmetic, keeping track of the relative amounts of fruit in two baskets after multiple changes. The rare combination of memory and problem solving can explain some of elephants' most clever behaviors, but it doesn't explain some of the things we're just beginning to learn about their mental lives. Elephants communicate using everything from body signals and vocalizations, to infrasound rumbles that can be heard kilometers away. And their understanding of syntax suggests that they have their own language and grammar. This sense of language may even go beyond simple communication. Elephants create art by carefully choosing and combining different colors and elements. They can also recognize twelve distinct tones of music and recreate melodies. And yes, there is an elephant band.

It is the hippocampus, strongly associated with emotion, that aids recollection by encoding important experiences into long-term memories. The ability to distinguish this importance makes elephant memory a complex and adaptable faculty beyond rote memorization. It's what allows elephants who survived a drought in their youth to recognize its warning signs in adulthood, which is why clans with older matriarchs have higher survival rates.Unfortunately, it's also what makes elephants one of the few non-human animals to suffer from post-traumatic stress disorder.

Looking inside their heads, we can see why. The elephant boasts the largest brain of any land mammal, as well as an impressive encephalization quotient. This is the size of the brain relative to what we'd expect for an animal's body size, and the elephant's EQ is nearly as high as a chimpanzee's. And despite the distant relation, convergent evolution has made it remarkably similar to the human brain, with as many neurons and synapses and a highly developed hippocampus and cerebral cortex.

Elephants remember not only their herd companions but other creatures who have made a strong impression on them. In one case, two circus elephants that had briefly performed together rejoiced when crossing paths 23 years later.This recognition isn't limited to others of their species. Elephants have also recognized humans they've bonded with after decades apart. All of this shows that elephant memory goes beyond responses to stimuli.

Unlike many proverbs, the one about elephant memory is scientifically accurate. Elephants know every member in their herd, able to recognize as many as 30 companions by sight or smell. This is a great help when migrating or encountering other potentially hostile elephants. They also remember and distinguish particular cues that signal danger and can recall important locations long after their last visit. But it's the memories unrelated to survival that are the most fascinating.

It's a common saying that elephants never forget, but these magnificent animals are more than giant walking hard drives. The more we learn about elephants, the more it appears that their impressive memory is only one aspect of an incredible intelligence that makes them some of the most social, creative, and benevolent creatures on Earth.