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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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The Sweet Surprise Reunion Mr. Rogers Never Saw Coming
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For more than 30 years, legendary children’s show host Fred Rogers used his PBS series Mister Rogers’ Neighborhood to educate his young viewers on concepts like empathy, sharing, and grief. As a result, he won just about every television award he was eligible for, some of them many times over.

Rogers was gracious in accepting each, but according to those who were close to the host, one honor in particular stood out. It was March 11, 1999, and Rogers was being inducted into the Television Academy Hall of Fame, an offshoot of the Emmy Awards. Just before being called to the stage, out came a surprise.

The man responsible for the elation on Rogers’s face was Jeff Erlanger, a 29-year-old from Madison, Wisconsin who became a quadriplegic at a young age after undergoing spinal surgery to remove a tumor. Rogers was surprised because Erlanger had appeared on his show nearly 20 years prior in 1980 to help kids understand how people with physical challenges adapt to life’s challenges. Here's his first encounter with the host:

Reunited on stage after two decades, Erlanger referred to the song, “It’s You I Like,” which the two sang during their initial meeting. “On behalf of millions of children and grown-ups,” Erlanger said, “it’s you I like.” The audience, including a visibly moved Candice Bergen, rose to their feet to give both men a standing ovation.

Following Erlanger’s death in 2007, Hedda Sharapan, an employee with Rogers’s production company, called their poignant scene “authentic” and “unscripted,” and that Rogers often pointed to it as his favorite moment from the series.

Near the end of the original segment in 1980, as Erlanger drives his wheelchair off-camera, Rogers waves goodbye and offers a departing message: “I hope you’ll come back to visit again.”

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20 Things You Might Not Have Known About Firefly
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© 2002 Twentieth Century Fox

As any diehard fan will be quick to tell you, Firefly's run was far, far too short. Despite its truncated run, the show still offers a wealth of fun facts and hidden Easter eggs. On the 15th anniversary of the series' premiere, we're looking back at the sci-fi series that kickstarted a Browncoat revolution.

1. A CIVIL WAR NOVEL INSPIRED THE FIREFLY UNIVERSE.

The Pulitzer Prize-winning novel The Killer Angels from author Michael Shaara was Joss Whedon’s inspiration for creating Firefly. It follows Union and Confederate soldiers during four days at the Battle of Gettysburg during the American Civil War. Whedon modeled the series and world on the Reconstruction Era, but set in the future.

2. ORIGINALLY, THE SERENITY CREW INCLUDED JUST FIVE MEMBERS.

When Whedon first developed Firefly, he wanted Serenity to only have five crew members. However, throughout development and casting, Whedon increased the cast from five to nine.

3. REBECCA GAYHEART WAS ORIGINALLY CAST TO PLAY INARA.

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Before Morena Baccarin was cast as Inara Serra, Rebecca Gayheart landed the role—but she was fired after one day of shooting because she lacked chemistry with the rest of the cast. Baccarin was cast two days later and started shooting that day.

4. NEIL PATRICK HARRIS WAS ALMOST DR. SIMON TAM.

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Before it went to Sean Maher, Neil Patrick Harris auditioned for the role of Dr. Simon Tam.

5. JOSS WHEDON WROTE THE THEME SONG.

Whedon wrote the lyrics and music for Firefly’s opening theme song, “The Ballad of Serenity.”

6. STAR WARS SPACECRAFT APPEAR IN FIREFLY.

Star Wars was a big influence on Whedon. Captain Malcolm Reynolds somewhat resembles Han Solo, while Whedon used the Millennium Falcon as inspiration to create Serenity. In fact, you can spot a few spacecraft from George Lucas's magnum opus on the show.

When Inara’s shuttle docks with Serenity in the pilot episode, an Imperial Shuttle can be found flying in the background. In the episode “Shindig,” you can see a Starlight Intruder as the crew lands on the planet Persephone.

7. HAN SOLO FROZEN IN CARBONITE POPS UP THROUGHOUT FIREFLY.

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Nathan Fillion is a big Han Solo fan, so the Firefly prop department made a 12-inch replica of Han Solo encased in Carbonite for the Canadian-born actor. You can see the prop in the background in a number of scenes.

8. ALIEN'S WEYLAND-YUTANI CORPORATION MADE AN APPEARANCE.

In Firefly’s pilot episode, the opening scene features the legendary Battle of Serenity Valley between the Browncoats and The Union of Allied Planets. Captain Malcolm Reynolds takes control of a cannon with a Weyland-Yutani logo inside of its display. Weyland-Yutani is the large conglomerate corporation in the Alien film franchise. (Whedon wrote Alien: Resurrection in 1997.)

9. ZAC EFRON'S ACTING DEBUT WAS ON FIREFLY.

A 13-year-old Zac Efron made his acting debut in the episode “Safe” in 2002. He played Young Simon in a flashback.

10. CAPTAIN MALCOLM REYNOLDS'S HORSE IS A WESTERN TROPE.

At its core, Firefly is a sci-fi western—and Malcolm Reynolds rides the same horse on every planet (it's named Fred).

11. FOX AIRED FIREFLY'S EPISODES OUT OF ORDER.

Fox didn’t feel Firefly’s two-hour pilot episode was strong enough to air as its first episode. Instead, “The Train Job” was broadcast first because it featured more action and excitement. The network continued to cherry-pick episodes based on broad appeal rather than story consistency, and eventually aired the pilot as the show’s final episode.

12. THE ALLIANCE'S ORIGINS ARE AMERICAN AND CHINESE.

The full name of The Alliance is The Anglo-Sino Alliance. Whedon envisioned The Alliance as a merger of American and Chinese government and corporate superpowers. The Union of Allied Planets’ flag is a blending of the American and Chinese national flags.

13. THE SERENITY LOUNGE SERVED AS AN ACTUAL LOUNGE.

Between set-ups and shots, the cast would hang out in the lounge on the Serenity set rather than trailers or green rooms.

14. INARA SERRA'S NAME IS MESOPOTAMIAN.

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Inara Serra is named after the Mesopotamian Hittite goddess, the protector of all wild animals.

15. THE CHARACTERS SWORE (JUST NOT IN ENGLISH).

The Firefly universe is a mixture of American and Chinese culture, which made it easy for writers to get around censors by having characters swear in Chinese.

16. THE UNIFORMS ARE RECYCLED FROM STARSHIP TROOPERS.

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The uniforms for Alliance officers and soldiers were the costumes from the 1997 science fiction film Starship Troopers. The same costumes were repurposed again for the Starship Troopers sequel.

17. "SUMMER!" MEANS SOMEONE MESSED UP.

Every time a cast member flubbed one of his or her lines, they would yell Summer Glau’s name. This was a running gag among the cast after Glau forgot her lines in the episode “Objects In Space.”

18. THE SERENITY SPACESHIP WAS BUILT TO SCALE.

The interior of Serenity was built entirely to scale; rooms and sections were completely contiguous. The ship’s interior was split into two stages, one for the upper deck and one for the lower. Whedon showed off the Firefly set in one long take to open the Serenity movie.

19. "THE MESSAGE" SHOULD HAVE BEEN THE SHOW'S FAREWELL.

Although “The Message” was the twelfth episode, it was the last episode filmed during Firefly’s short run. Composer Greg Edmonson wrote a piece of music for a funeral scene in the episode, which served as a final farewell to the show. Sadly, it was one of three episodes (the other two were “Trash” and “Heart of Gold”) that didn’t air during Firefly’s original broadcast run on Fox.

20. FIREFLY AND SERENITY WERE SENT TO THE INTERNATIONAL SPACE STATION.

American Astronaut Steven Ray Swanson is a big fan of Firefly, so when he was sent to the International Space Station for his first mission (STS-117) in 2007, he brought DVD copies of Firefly and its feature film Serenity aboard with him. The DVDs are now a permanent part of the space station’s library.

This post originally appeared in 2014.

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