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Domesticating horses completely  changed the way that people lived, traded goods, and fought battles. And from the earliest known efforts  to domesticate a horse species, some 5500 years ago, until trains  were invented about 200 years ago, horses were the fastest way to travel on land.

For years, scientists have wondered  where modern domesticated horses come from, both genetically and geographically. And a new paper published in  Nature might have the answer. An international team of researchers  looked at DNA from the remains of 273 ancient horses spanning 50,000 years of  history and all the regions that have been hypothesized as the center of horse domestication.

They found remains of the earliest horses  that were genetically similar to modern horses in the Volga-Dom  area of what is now Russia. These horses lived about 4600 to 5500 years ago. That genotype didn’t start showing up in  other regions until about 4200 years ago, suggesting that is the point that  modern horses began to spread.

They also screened for two  genes that might explain why these were the horses that won out. One of the genes is associated with  chronic back pain and painful walking in humans, and the other is associated  with fear and aggression in mice. The researchers propose that those  genes made this new type of horse more docile and able to handle stress, and  made them better at bearing weight and endurance running, all things  you want in a domesticated horse.

But this discovery tells us about  a lot more than ancient horses. It tells us about ancient people. By combining this genetic information  with other archaeological evidence and mythology, we can learn more  about how human populations interacted with each other.

Human DNA suggests that people  from Western Eurasia moved into Europe between 2900 and 2300 BCE. And scientists used to think that  domesticating horses is what let that happen. Because it meant that the people from.

Eurasia could use horse-mounted warfare  to dominate the local populations. But there’s not really any DNA matching modern domesticated horses in Europe from that time. So it seems more likely  that the European population had already declined, allowing people  from Western Eurasia to just walk in.

The researchers also propose that  the people of the Volga-Dom region may have used their horses to conquer other civilizations because of a  need for more grazing land. Meanwhile, these docile horses  with fewer back injuries also made long-distance trade easier. Right now, it looks like the combination  of war and trade led to the newly domesticated horses completely replacing any other domesticated equine species  in less than about 1000 years.

But the researchers acknowledge that  there could be other evidence behind this rapid change that’s just harder to find. Which leaves us with now, where they are  the only domesticated horses we know. Meanwhile, scientists have  also been putting together archaeological remains, artifacts, and stories to understand the first European  settlement in the Americas.

The settlement is called L’Anse  aux Meadows and was built by the Norse at some point. From Icelandic sagas and  the style of architecture, researchers have estimated that the  site was probably built around 1000 CE, but no one has ever been able to  scientifically determine its precise age. Scientists have tried carbon dating  the artifacts from the settlement, but have gotten 150 different  dates spanning 273 years.

But that can’t be right, because the  archaeological evidence indicates that the Norse occupation of  this settlement was really short. This week, scientists announced in  Nature that they had used a new technique to pin the date of the  settlement to exactly 1021 CE. And the technique they used  actually relied on astronomy.

So how? Well carbon dating relies on  measuring the amount of a specific form of carbon called carbon-14 that’s slightly  radioactive and decays at a known rate. So if you measure the amount  of radioactive carbon-14, you can figure out how old an organic object is.

And now scientists can test very small areas. As small as, say, a single tree ring. And by stacking a bunch of rings together,  scientists can use science you might have learned in grade school  to tell how old the tree is.

Through carbon dating of tree rings,  scientists have learned that carbon-14 production usually varies by  less than 2 percent year-to-year. But sometimes, there will be a year with a 10  to 12 percent change from the previous year. That is because cosmic radiation events,  like solar flares and coronal mass ejections, cause a spike in the  amount of carbon-14 in the atmosphere.

And when that happens, that  spike can be seen in the ring that corresponds to that year. By counting the rings of wood  with a known age, scientists were able to figure out that there were cosmic  radiation events in 775 and 993 CE. So an international team of  researchers took three wooden artifacts that included that event in 993  from the L’Anse aux Meadows site.

Because dating tree rings isn't as simple  as looking up the reference in a giant index, scientists first had to use carbon  dating to figure out the range of possible dates for the very outermost ring,  part of the live edge of the wood. Once they had that range of dates, they  knew that the radiation anomaly of 993 would be between 26 and 31 rings, or years,  back. So, they started counting back.

In all three of the artifacts, there was a  big drop in carbon 14 in ring 29, telling the scientists that that’s the ring  from the year before the cosmic radiation event, AKA 992. 992 plus 29 years places all three of the   objects being made and the trees  being cut down in the year 1021. This specific year gives us a new reference  point for thinking about when Europe became aware of the Americas,  as well as context for interactions with local Indigenous populations, disease transmission, and the  introduction of foreign plants or animals. It also shows that using cosmic radiation  events can be an effective way of dating objects, which opens the doors to learning  a lot more about other archaeological sites and the people who lived there.

I hope you enjoyed this episode of  SciShow, and thank you for watching. And thanks to this month’s President  of Science, Matthew Brant! We really appreciate your  support in helping us create educational videos like this one.

If you would like to learn more about  joining our awesome community of patrons, you can check it out at Patreon.com/SciShow. [♪ OUTRO].