字幕列表 影片播放 列印英文字幕 In 1600, William Gilbert published a paper detailing how Earth behaves as a giant magnet. That seems like a long time ago, but in geologic time, that's nothing. It's taken hundreds of years to understand how Earth's magnetic field works… but now that we do, scientists are trying to find hints from Earth's history that might reveal the future of this ever-changing invisible field all around us. Specifically, archaeologists are studying the handles of ancient pottery. Yeah. But before I can explain it, we have to get to how the field affects you. Scientists believe Earth's magnetic field is generated by the spinning of the Earth's core. Our planet's magnetic field is super important, as it blocks harmful rays emanating out of the sun from hitting us on the ground, destroying the possibility of life as we know it. No big deal. It's always around us, and it strengthens and weakens over time -- sometimes, it even flips. If it were to flip, the magnetic north pole would become the south, and suddenly all magnetic compasses in the world would be backwards. Everything else would be fine though. It's not like it would turn off and back on. NASA knows a magnetic field flip happens about every two to three hundred-thousand years. We know the magnetic field has flipped, because there's evidence in the geologic record. Scientists pulled lava from the Mid-Atlantic Ridge, where two tectonic plates meet. The ridge is spreading, giving easy access to very old, cooled lava flows. Minerals embedded in the lava are sensitive to Earth's magnetic field as the lava cools, so, by collecting samples of lava, called “cores,” and analyzing the rock... I think you see where this is going… It reveals a record of Earth's magnetic field over hundreds of thousands of years. This shows the last “major field flip was about 780,000 years ago.” The problem is, cooling lava rock can't be precisely dated... Lava rocks don't have timecodes or calendar reminders detailing when they oozed and then cooled. Geologic timescales can encompass thousands of years at a time, meaning we know this lava cooled within a few millennia of whatever… So, while these rocks can give us an ancient picture of the magnetic field, imagine a pictures that is really zoomed out, or blurry! We definitely would need a better image to fully understand whats happening. Now, a paper published in the Proceedings of the National Academy of Sciences in February 2017, found a way to enhance this hypothetical image by using ancient pottery. Clay is also subject to the same Earth's magnetic field record keeping, but the dates are far more precise. So, by analyzing the clay in 67 jar handles from the Iron Age kingdom of Judah, archaeologists have found evidence of the magnetic field strength rising and falling over the 600 years preceding 200 BCE! All from jar handles made of clay! The results were so clear, they could map the field picture down to a span of give or take 15 years. Imagine how much clearer a 15 year picture is compared to a 1000 year picture from geologic time! It looks like Earth's magnetic field strength was super high in the 8th century BCE, then weakened from the 6th to 2nd century BCE. The kicker for making this picture so clear, was the precise dating on the jar handle because of royal stamps present on the handles of these 67 jars. . Similar to how writing technology has gotten better since the Sumerians in 3000 BCE; over time, stamp technology has changed… allowing the archaeologists to give atmospheric and cosmological scientists a leg up in studying magnetic fields by precisely dating when things changed, and of, by proxy, giving physicists studying the interior movement of the Earth a little bit of help too. A magnetic field flip is coming! Exact magnetic north has moved more than 600 miles further north since it was first pegged in the early 19th century, first at about 10 miles per year , and now closer to 40 miles per year! On top of that, the field has lost “10 percent of its strength over the last two centuries” This causes more vibrant aurora, but don't fret. The field continues to shield the surface of the planet from harmful charged particles, and has the thick atmosphere to catch any that may eek through. Long story short, go take a pottery class. You might help scientists thousands of years in the future! We can't do episodes like this without our sponsors. Thanks to Graze for sponsoring this episode. Graze makes snacking exciting by combining wholesome ingredients with flavors we all love, to create over 100 nutritionist-approved snacks. Go to graze.com and enter promo code SEEKER to get a free, sampler box delivered to your home or work. When the magnetic field flip does happen. Earth's magnetic north will become magnetic south, and all the compasses in the world, and any technology based on that, would be backwards! You want to know more about our magnetic field reversals? Tara's got you, right here. Got a science question? Let us know down in the comments and please subscribe so you get more videos from us. Thanks for watching!