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10 Methods Scientists Use to Date Things

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Left and right, archaeologists are radiocarbon dating objects: fossils, documents, shrouds of Turin. They do it by comparing the ratio of an unstable isotope, carbon-14, to the normal, stable carbon-12. All living things have about the same level of carbon-14, but when they die it begins to decay at uniform rate—the half-life is about 5,700 years, and you can use this knowledge to date objects back about 60,000 years.

However, radiocarbon dating is hardly the only method that creative archaeologists and paleontologists have at their disposal for estimating ages and sorting out the past. Some are plainly obvious, like the clockwork rings of many old trees. But there are plenty of strange and expected ways to learn about the past form the clues it left behind.

1. Camel on Your Knife

It's wasn't so long ago that megafauna ruled the American continent. Sloths and wooly mammoths pushed their weight around; horses and camels had their day. But after the end of the last Ice Age those animals disappeared, so when scientists turn up traces of those animals on archaeological remains, those remains go way back.

Last year, the University of Colorado's Doug Bamforth analyzed a cache of 80-plus tools that a Boulder, Colorado, man accidentally unearthed in his yard. Those tools showed protein residue from camels and horses, so Bamforth dated them to the Clovis people who lived around about 13,000 years ago. (Not all scientists accept the accuracy of these tests, but that's nothing new in archaeology).

2. Locked Away DNA

Medieval manuscripts have a lot more to say than simply the words on their pages; often they're written on parchment made from animal skins, and organic material keeps its secrets for a long time. Literary historian Timothy Stinson developed a way to extract the DNA from parchment itself, and if you can tell what animal a parchment was derived from, you might be able to tell more about what time and place the document originated.

3. The Secret Life of Dung

Moa, the giant flightless birds of New Zealand, may have been extinct for at least 500 years, but their dung is surprisingly resilient. On cave floors and buried in shelters, researchers found dung from the moa, with some of the samples being 15 cm (nearly six inches) in length. The contents of the droppings give more than a window into the giant bird's eating habits—they preserve a record of what the long-gone moa's ecosystem was like.

The arid conditions of New Zealand caves provide the perfect place for poo preservation. Australia should, too, the researchers say, but the droppings of ancient marsupials just haven't turned up. As professor Alan Cooper says, "A key question for us is 'where has all the Australian poo gone?'"

4. Nuclear Forensics

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If you think your metal detector has uncovered some treasures, try finding vintage plutonium in the backyard. Jon Schwantes of the Pacific Northwest National Laboratory was called in to analyze a sample of plutonium-239 accidentally discovered in a safe during the cleanup of the Hanford nuclear site in Washington. One clue was the "signature" left by the reactor—every reactor's is different. The fingerprint of this discarded material led him to a reactor not in Hanford, but in Oak Ridge, TN. It also led him to the conclusion that it was created in 1944, meaning it was created during the Manhattan Project, making it one of the world's oldest-known samples of enriched plutonium. [Image courtesy of Popular Mechanics.]

5. Chemical Warfare

A pile of skeletons probably wouldn't tell us much more than the obvious. But University of Leicester archaeologist Simon James sees evidence that, to him, dates the first known chemical warfare attack back to 256 A.D.

In that year, Persians attacked a Roman garrison at Dura-Europos in Syria; when they tried to mine under the walls, Romans tried to counter by mining under the Persian tunnels. Archaeologists found the pile of Roman bodies in one of the tunnels, but no cause of death. James thinks it was asphyxiation. In the tunnels, he says, there was bitumen and sulfur—materials that, when burned, give off toxic gas. So, he says, the Persians probably used chemical warfare to do in their rivals.

6. The Magnetic Fields

One classical way to date objects is to take note of what strata of rock they occupy—rocks come in layers, with the oldest at the bottom. But those rocks also carry less obvious information—their magnetic signatures. The Earth's magnetic field varies all the time, by both strength and orientation. At the time rocks form, however, their magnetic materials acquire the particular orientation of the planet's magnetism at the time, giving geologists a window into the Earth's magnetic past.

7. Ice Cores

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You've probably heard about ice cores, but what are they exactly? Ice sheets are laid down in layers, and the layer corresponding to each year is a little different. The important thing for climate researchers is that the oxygen isotopes present in a layer can help show what the temperature was that year. So by extracting a cylindrical core sample containing layers that go way back, they can build a model of the climate of the past. [Image courtesy of AccuWeather.com.]

8. Pollen

Finally, pollen is good for something besides making you sneeze. Deposits of pollen deep in the ground can reveal what the vegetation was like at that time, and ergo, what the area's climate might have been like. Radiocarbon dating has become the standard method to date organic material, making pollen deposits sort of useless in that regard. But pollen can still help scientists interpret the environment of the past.

9. Volcanic Ash

Everything, it seems, has a fingerprint, and volcanoes are no exception—each eruption contains a chemical mix that is all its own. So if you knew the specific signature of say, the 79 A.D. eruption of Mt Vesuvius that buried Pompeii, you could look for that signature elsewhere in Italy and know that it came from the same eruption. Thus, any objects in that "tephra," the name for solids ejected during a single eruption, date to that era of Roman history, and anything below it would be older. This dating system is called tephrochronology.

10. Thermoluminescence

You probably know that radiation you can't see is flying all around you, but you might not know that not only do objects absorb that radiation, they also let their trapped radiation go when heated up. Knowing this, an archaeologist could heat up an object, watch how much radiation is released and determine how old the thing might be.

It's particularly useful for ceramics. When a potter in Ancient Greece fired his kiln and baked a pot, that released the clay's stored electrons and reset the clock to zero. During all those centuries it sat in the ground, it began storing radiation again at a steady rate. So when a curious 21st century scientist unearths the pot and heats it again, she can measure the radiation released, crunch some numbers and figure out how long ago the pot was first fired.

Andrew Moseman writes about science for publications like Popular Mechanics, Discover, Scientific American and Big Think from his Brooklyn apartment beneath the elevated tracks. He's from Nebraska, and he claims that ex-Huskers are starting a hive in New York City. Just so you know.

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8 of the Weirdest Gallup Polls
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Born in Jefferson, Iowa on November 18, 1901, George Gallup studied journalism and psychology, focusing on how to measure readers’ interest in newspaper and magazine content. In 1935, he founded the American Institute of Public Opinion to scientifically measure public opinions on topics such as government spending, criminal justice, and presidential candidates. Although he died in 1984, The Gallup Poll continues his legacy of trying to determine and report the will of the people in an unbiased, independent way. To celebrate his day of birth, we compiled a list of some of the weirdest, funniest Gallup polls over the years.

1. THREE IN FOUR AMERICANS BELIEVE IN THE PARANORMAL (2005)

According to this Gallup poll, 75 percent of Americans have at least one paranormal belief. Specifically, 41 percent believe in extrasensory perception (ESP), 37 percent believe in haunted houses, and 21 percent believe in witches. What about channeling spirits, you might ask? Only 9 percent of Americans believe that it’s possible to channel a spirit so that it takes temporary control of one's body. Interestingly, believing in paranormal phenomena was relatively similar across people of different genders, races, ages, and education levels.

2. ONE IN FIVE AMERICANS THINK THE SUN REVOLVES AROUND THE EARTH (1999)

In this poll, Gallup tried to determine the popularity of heliocentric versus geocentric views. While 79 percent of Americans correctly stated that the Earth revolves around the sun, 18 percent think the sun revolves around the Earth. Three percent chose to remain indifferent, saying they had no opinion either way.

3. 22 PERCENT OF AMERICANS ARE HESITANT TO SUPPORT A MORMON (2011)

Gallup first measured anti-Mormon sentiment back in 1967, and it was still an issue in 2011, a year before Mormon Mitt Romney ran for president. Approximately 22 percent of Americans said they would not vote for a Mormon presidential candidate, even if that candidate belonged to their preferred political party. Strangely, Americans’ bias against Mormons has remained stable since the 1960s, despite decreasing bias against African Americans, Catholics, Jews, and women.

4. MISSISSIPPIANS GO TO CHURCH THE MOST; VERMONTERS THE LEAST (2010)

This 2010 poll amusingly confirms the stereotype that southerners are more religious than the rest of the country. Although 42 percent of all Americans attend church regularly (which Gallup defines as weekly or almost weekly), there are large variations based on geography. For example, 63 percent of people in Mississippi attend church regularly, followed by 58 percent in Alabama and 56 percent in South Carolina, Louisiana, and Utah. Rounding out the lowest levels of church attendance, on the other hand, were Vermont, where 23 percent of residents attend church regularly, New Hampshire, at 26 percent, and Maine at 27 percent.

5. ONE IN FOUR AMERICANS DON’T KNOW WHICH COUNTRY AMERICA GAINED INDEPENDENCE FROM (1999)

Although 76 percent of Americans knew that the United States gained independence from Great Britain as a result of the Revolutionary War, 24 percent weren’t so sure. Two percent thought the correct answer was France, 3 percent said a different country (such as Mexico, China, or Russia), and 19 percent had no opinion. Certain groups of people who consider themselves patriotic, including men, older people, and white people (according to Gallup polls), were more likely to know that America gained its independence from Great Britain.

6. ONE THIRD OF AMERICANS BELIEVE IN GHOSTS (2000)

This Halloween-themed Gallup poll asked Americans about their habits and behavior on the last day of October. Predictably, two-thirds of Americans reported that someone in their house planned to give candy to trick-or-treaters and more than three-quarters of parents with kids reported that their kids would wear a costume. More surprisingly, 31 percent of American adults claimed to believe in ghosts, an increase from 1978, when only 11 percent of American adults admitted to a belief in ghosts.

7. 5 PERCENT OF WORKING MILLENNIALS THRIVE IN ALL FIVE ELEMENTS OF WELL-BEING (2016)

This recent Gallup poll is funny in a sad way, as it sheds light on the tragicomic life of a millennial. In this poll, well-being is defined as having purpose, social support, manageable finances, a strong community, and good physical health. Sadly, only 5 percent of working millennials—defined as people born between 1980 and 1996—were thriving in these five indicators of well-being. To counter this lack of well-being, Gallup’s report recommends that managers promote work-life balance and improve their communication with millennial employees.

8. THE WORLD IS BECOMING SLIGHTLY MORE NEGATIVE (2014)

If you seem to feel more stress, sadness, anxiety, and pain than ever before, Gallup has the proof that it’s not all in your head. According to the company’s worldwide negative experience index, negative feelings such as stress, sadness, and anger have increased since 2007. Unsurprisingly, people living in war-torn, dangerous parts of the word—Iraq, Iran, Egypt, Syria, and Sierra Leone—reported the highest levels of negative emotions.

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11 Times Mickey Mouse Was Banned
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Despite being one of the world’s most recognizable and beloved characters, it hasn’t always been smooth sailing for Mickey Mouse, who turns 89 years old today. A number of countries—and even U.S. states—have banned the cartoon rodent at one time or another for reasons both big and small.

1. In 1930, Ohio banned a cartoon called “The Shindig” because Clarabelle Cow was shown reading Three Weeks by Elinor Glyn, the premier romance novelist of the time. Check it out (1:05) and let us know if you’re scandalized:

2. With movies on 10-foot screen being a relatively new thing in Romania in 1935, the government decided to ban Mickey Mouse, concerned that children would be terrified of a monstrous rodent.

3. In 1929, a German censor banned a Mickey Mouse short called “The Barnyard Battle.” The reason? An army of cats wearing pickelhauben, the pointed helmets worn by German military in the 19th and 20th centuries: "The wearing of German military helmets by an army of cats which oppose a militia of mice is offensive to national dignity. Permission to exhibit this production in Germany is refused.”

4. The German dislike for Mickey Mouse continued into the mid-'30s, with one German newspaper wondering why such a small and dirty animal would be idolized by children across the world: "Mickey Mouse is the most miserable ideal ever revealed ... Healthy emotions tell every independent young man and every honorable youth that the dirty and filth-covered vermin, the greatest bacteria carrier in the animal kingdom, cannot be the ideal type of animal.” Mickey was originally banned from Nazi Germany, but eventually the mouse's popularity won out.

5. In 2014, Iran's Organization for Supporting Manufacturers and Consumers announced a ban on school supplies and stationery products featuring “demoralizing images,” including that of Disney characters such as Mickey Mouse, Winnie the Pooh, Sleeping Beauty, and characters from Toy Story.

6. In 1954, East Germany banned Mickey Mouse comics, claiming that Mickey was an “anti-Red rebel.”

7. In 1937, a Mickey Mouse adventure was so similar to real events in Yugoslavia that the comic strip was banned. State police say the comic strip depicted a “Puritan-like revolt” that was a danger to the “Boy King,” Peter II of Yugoslavia, who was just 14 at the time. A journalist who wrote about the ban was consequently escorted out of the country.

8. Though Mussolini banned many cartoons and American influences from Italy in 1938, Mickey Mouse flew under the radar. It’s been said that Mussolini’s children were such Mickey Mouse fans that they were able to convince him to keep the rodent around.

9. Mickey and his friends were banned from the 1988 Seoul Olympics in a roundabout way. As they do with many major sporting events, including the Super Bowl, Disney had contacted American favorites to win in each event to ask them to say the famous “I’m going to Disneyland!” line if they won. When American swimmer Matt Biondi won the 100-meter freestyle, he dutifully complied with the request. After a complaint from the East Germans, the tape was pulled and given to the International Olympic Committee.

10. In 1993, Mickey was banned from a place he shouldn't have been in the first place: Seattle liquor stores. As a wonderful opening sentence from the Associated Press explained, "Mickey Mouse, the Easter Bunny and teddy bears have no business selling booze, the Washington State Liquor Control Board has decided." A handful of stores had painted Mickey and other characters as part of a promotion. A Disney VP said Mickey was "a nondrinker."

11. Let's end with another strike against The Shindig (see #1) and Clarabelle’s bulging udder. Less than a year after the Shindig ban, the Motion Picture Producers and Directors of America announced that they had received a massive number of complaints about the engorged cow udders in various Mickey Mouse cartoons.

From then on, according to a 1931 article in Time magazine, “Cows in Mickey Mouse ... pictures in the future will have small or invisible udders quite unlike the gargantuan organ whose antics of late have shocked some and convulsed others. In a recent picture the udder, besides flying violently to left and right or stretching far out behind when the cow was in motion, heaved with its panting with the cow stood still.”

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