Dead people. They've been around the block and today on SciShow News, dead person wisdom is helping to enrich our understanding of the natural world. For starters, how in Odin's name did Vikings manage to be such awesome navigators? Medieval Chinese explorers used the first magnetic compasses and Mediterranean sailors used the sun, but historians have longed scratched their heads over how Vikings so readily found their way through foggy, often sunless Northern seas. Vikings sailed as far South as Africa, as far East as Siberia and they beat Columbus to the Americas by hundreds of years. Well, Viking legend has it that they used a gem called a sunstone to reveal the position of the sun through fog, clouds, pre-light and twilight. But Viking legend also has it that people are made out of driftwood. However, three years ago, divers found a crystal among navigation tools on a sixteenth century English shipwreck off the island of Alderney. Physicists from France's University of Rennes studied the card deck shaped crystal and found it to be Icelandic Spar, a type of calcite. And the crystal had an unusual property called birefringence. It creates a double refraction of light revealing the direction of the lights source to within one degree of accuracy and its in dull light, even when the sun is below the horizon. Reporting in the proceedings of the Royal Academy A, the physicists say that they believe the were using the stone as a solar compass. We've yet to find anything like the crystal in a Viking shipwreck, though fragments of Icelandic Spar were found last year in a Viking settlement. The authors of the study say that a sunstone has probably never been discovered until now because the crystal's structure is so fragile. But compasses it appears are nothing new. And neither is heart disease. Gerontologists from the University of Southern California revealed in the Lancet on Sunday that arteries of mummies discovered all over the world are just as clogged as ours. Atherosclerosis is the number one cause of death in the developed world, causing blood clots, heart attacks and strokes. For it's prevalence we've blamed tobacco, pepperoni pizza, and the ability to just get into your car and drive to the grocery store that's just two blocks down the street, people. But CT scans revealed that 137 mummies hailing from 4 continents and spanning 4,000 years of history had clogged arteries too. Though a daily double bacon doughnut burger and a sedentary lifestyle probably accelerated atherosclerosis, it appears that there's more to it than that. The mummies had a wide range of diets and lifestyles, Peruvian mummies, Aleutian mummies and mummies from the Southwestern US had been normal people in life mummified by naturally cold or dry conditions. And Egyptian mummies were mummified intentionally because of there status as aristocrats. Despite the differences in lifestyle, all of the mummies should about the same level of atherosclerosis. One group that did show more signs of the condition was the elderly. In all populations, there is a connection between the disease and age, which suggests that calcium build-up in the arteries is somehow inherent, just part of growing older. You're demise is inevitable. And that note thank you for watching this episode of SciShow. If you want to keep up to date on the all the breaking news you can go to youtube.com/scishow and subscribe. And if you have any questions or ideas, we're on Facebook and Twitter and down in the comments below. We'll see you next time. BAM!