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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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Paw Enforcement: A History of McGruff the Crime Dog
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Jack Keil, executive creative director of the Dancer Fitzgerald Sample ad agency, was stuck in a Kansas City airport at three in the morning when he started thinking about Smokey Bear. Smokey was the furred face of forest fire prevention, an amiable creature who cautioned against the hazards of unattended campfires or errant cigarette butts. Everyone, it seemed, knew Smokey and heeded his words.

In 1979, Keil’s agency had been tasked with coming up with a campaign for the recently-instituted National Crime Prevention Council (NCPC), a nonprofit organization looking to educate the public about crime prevention. If Keil could create a Smokey for their mission, he figured he would have a hit. He considered an elephant who could stamp out crime, or a rabbit who was hopping mad about illegal activity.

A dog seemed to fit. Dogs bit things, and the NCPC was looking to take a bite out of crime. Keil sketched a dog reminiscent of Snoopy with a Keystone Cop-style hat.

Back at the agency, people loved the idea but hated the dog. In a week’s time, the cartoon animal would morph into McGruff, the world-weary detective who has raised awareness about everything from kidnapping to drug abuse. While he no longer looked like Snoopy, he was about to become just as famous.

In 1979, the public service advertising nonprofit the Ad Council held a meeting to discuss American paranoia. Crime was a hot button issue, with sensational reports about drugs, home invasions, and murders taking up the covers of major media outlets like Newsweek and TIME. Surveys reported that citizens were concerned about crime rates and neighborhood safety. Respondents felt helpless to do anything, since more law enforcement meant increased taxes.

To combat public perception, the Ad Council wanted to commit to an advertising campaign that would act as a preventive measure. Crime could not be stopped, but the feeling was that it could be dented with more informed communities. Maybe a clean park would be less inviting to criminals; people might need to be reminded to lock their doors.

What people did not need was a lecture. So the council enlisted Dancer Fitzgerald Sample to organize a campaign that promoted awareness in the most gentle way possible. Keil's colleagues weighed in on his dog idea; someone suggested that the canine be modeled after J. Edgar Hoover, another saw a Superman-esque dog that would fly in to interrupt crime. Sherry Nemmers and Ray Krivascy offered an alternative take: a dog wearing a trench coat and smoking a cigar, modeled in part after Peter Falk’s performance as the rumpled TV detective Columbo.

Keil had designs on getting Falk to voice the animated character, but the actor’s methodical delivery wasn’t suited to 30-second commercials, so Keil did it himself. His scratchy voice lent an authoritarian tone, but wasn't over-the-top.

The agency ran a contest on the back of cereal boxes to name the dog. “Sherlock Bones” was the most common submission, but "McGruff"—which was suggested by a New Orleans police officer—won out.

Armed with a look, a voice, and a name, Nemmers arranged for a series of ads to run in the fall of 1980. In the spots, McGruff was superimposed over scenes of a burglary and children wary of being kidnapped by men in weather-beaten cars. He advised people to call the police if they spotted something suspicious—like strangers taking off with the neighbor’s television or sofa—and to keep their doors locked. He sat at a piano and sang “users are losers” in reference to drug-abusing adolescents. (The cigar had been scrapped.)

Most importantly, the NCPC—which had taken over responsibility for McGruff's message—wanted the ads to have what the industry dubbed “fulfillment.” At the end, McGruff would advise viewers to write to a post office box for a booklet on how to prevent crime in their neck of the woods.

A lot of people did just that. More than 30,000 booklets went out during the first few months the ads aired. McGruff’s laconic presence was beginning to take off.

By 1988, an estimated 99 percent of children ages six to 12 recognized McGruff, putting him in Ronald McDonald territory. He appeared on the ABC series Webster, in parades, and in thousands of personal appearances around the country, typically with a local police officer under the suit. (The appearances were not without danger: Some dogs apparently didn't like McGruff and could get aggressive at the sight of him.)

As McGruff aged into the 1990s, his appearances grew more sporadic. The NCPC began targeting guns and drugs and wasn’t sure the cartoon dog was a good fit, so his appearances were limited to the end of some ad spots. By the 2000s, law enforcement cutbacks meant fewer cops in costume, and a reduced awareness of the crime-fighting canine. When Keil retired, an Iowa cop named Steve Parker took over McGruff's voice duties.

McGruff is still in action today, aiding in the NCPC’s efforts to raise awareness of elder abuse, internet crimes, and identity theft. The organization estimates that more than 4000 McGruffs are in circulation, though at least one of them failed to live up to the mantle. In 2014, a McGruff performer named John Morales pled guilty to possession of more than 1000 marijuana plants and a grenade launcher. He’s serving 16 years in prison.

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Watch a Panda Caretaker Cuddle With Baby Pandas While Dressed Up Like a Panda
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Some people wear suits to work—but at one Chinese nature reserve, a handful of lucky employees get to wear panda suits.

As Travel + Leisure reports, the People's Daily released a video in July of animal caretakers cuddling with baby pandas at the Wolong National Nature Reserve in China's Sichuan Province. The keepers dress in fuzzy black-and-white costumes—a sartorial choice that's equal parts adorable and imperative to the pandas' future success in the wild.

Researchers raise the pandas in captivity with the goal of eventually releasing them into their natural habitat. But according to The Atlantic, human attachment can hamper the pandas' survival chances, plus it can be stressful for the bears to interact with people. To keep the animals calm while acclimating them to forest life, the caretakers disguise their humanness with costumes, and even mask their smell by smearing the suits with panda urine and feces. Meanwhile, other keepers sometimes conceal themselves by dressing up as trees.

Below, you can watch the camouflaged panda caretakers as they cuddle baby pandas:

[h/t Travel + Leisure]

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