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This week on SciShow news Hank explains what Curiosity has found, . . .water on Mars!

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Sources for this episode:
http://www.pnas.org/content/early/2013/09/20/1308825110.full.pdf+html
http://www.eurekalert.org/jrnls/sci/summaries-09-27-13.php#A
http://www.pnas.org/cgi/doi/10.1073/pnas.1308825110
You probably already knew that Mars had water, and you probably already knew that human beings are predictable. But, until this week, no one knew that the surface of Mars is, in effect, covered in water, and human beings are so predictable that computers can actually forecast our history.

I'm Hank Green, and welcome to SciShow News..

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The Curiosity rover has been beating us over the head with its findings for the last couple of months. As such, it's released another chunk of very interesting data in this Thursday's issue of the journal Science. The results are from the first scoop of Martian soil Curiosity ever analyzed. In October 2012, it took a spoonful from a pile of dirt and dust named "Rocknest," heated it up in an oxygen-free chamber, and measured what gasses it gave off, using a gas chromatograph, mass spectrometer, and tunable laser spectrometer, which we talked about last week.

And it turns out, the soil has lots of water: 2% by weight, which is really high. Now, we knew that there was water on Mars. There's ice caps on the poles and a little water vapor in its atmosphere, but the fact that surface is covered in even small amounts of water, is pretty exciting. As the study's lead, Dr. Laurie Leshin said to the press, and I quote: "We now know there should be abundant, easily accessible water on Mars. When we send people, they could scoop up the soil anywhere on the surface, heat it just a bit, and obtain water." And if you're thinking that one sample can't be used as proof that there's water all over the place, keep listening. Because Curiosity also found compounds in its Rocknest sample that NASA thinks came from far away, mountainous areas.  Specifically, the ratio of isotopes and variations in elements in those compounds were very similar to ratios in Mars' atmosphere.  These findings suggest that the water was distributed, moved around the planet, which is a big deal.  Scientists are calling the surface of Mars the 'global layer', meaning that the surface oil gets picked up by dust storms and then redistributed.  So a scoop of dirt in one spot is an accurate model of Mars as a whole, and that model has a whole lot of water in it.

Another significant model this week had a lot of history in it.  A group of anthropologists and mathematicians joined forces to create a computer model that accurately predicated where and when complex societies, like empires and states, developed.  They published their results to the proceedings of the National Academy of Sciences on Monday.  The model was based on a map of Africa, Europe, and Asia around the year 1500 BCE, with a bunch of geographical and ecological factors put in, including what groups lived where.  The researchers also plugged in where and when certain innovations took place that had to do with warfare, like the invention of chariots or the domestication of horses.  Their hypothesis was that warfare encouraged the evolution of complex societies because the groups that worked together were the ones that survived wars.  So they put those factors to the test, running the model for 3,000 years forward to the year 1500, and the computer model predicted with 65% accuracy when and where large scale societies arose.  According to the scientists, this suggests that warfare is the driving force behind the evolution of large, complex societies, and also that to computers at least, warfare itself is pretty predictable.  The authors say it mostly comes down to geography, where people live in close proximity to each other and where they have fewer resources to share.  In fact, they note, historically one of the strongest indicators for warfare was your proximity to grasslands inhabited by nomads, especially if they were really good at riding horses, because they tended to roam farther and compete more for resources while spreading the technology of war.  Yes, we're looking at you, Mongols.  Even though the Mongols were the exception to many of the major trends in world history, in this case, they were the rule.  Using their innovations in warfare and making the most of their geography, they pillaged their way to becoming the most influential cultures in Eurasia.  So it looks like history isn't just a collection of random events after all.  There are larger mechanisms at work, and the better we understand these mechanisms, maybe we'll be better at shaping our future.  

Thank you for watching this episode of SciShow news.  If there's a news tip you have to share for us or something you'd like us to discuss, we're on Facebook and Twitter and down in the comments below, and don't forget to go to youtube.com/scishow and subscribe.

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