CLOSE
Original image
Thinkstock

How Long Does DNA Last?

Original image
Thinkstock

Even minimal exposure to forensic science on shows like CSI and NCIS will impress upon a viewer what a whopping big deal DNA analysis is. It’s the opposite of circumstantial evidence: undeniable proof of someone’s identity that is impossible to fake, short of swapping out one sample for another. The technique may be applied to murder victims or long-dead English kings or illegitimate children and their custody-dodging fathers—any subject from which intact genetic information can be extracted—and that's what makes DNA as valuable a tool in anthropological study as it is in police investigations. For a long-dead subject, DNA has an expiration date, but when exactly is it?

The entire formula for human life is encoded in the sub-microscopic molecules of deoxyribonucleic acid, and has been throughout all stages of evolution. Like fingerprints, genetic code is particular to an individual, which makes it a unique identifier in the absence of other information, like modern dental records. DNA, however, is fragile, and breaks down over time. How long the decomposition process takes will vary with the circumstances under which it is found. Take, for example, if DNA is exposed to the elements: Like the human body itself, DNA decays with increasing rapidity in the presence of heat, water, sunlight, and oxygen. Those essential conditions of life also speed the process of death, potentially rendering DNA useless for analysis in a matter of weeks.

Scientists have estimated that under the most ideal conditions, DNA can theoretically survive for a maximum of one million years. Although a team of researchers recently claimed to have discovered 419 million-year-old genetic material belonging to prehistoric bacteria in the Michigan Basin, others in the field have loudly contested the claim, especially in light of an earlier sample thought to be 250 million years old, but later proven contaminated by the presence of modern DNA. The oldest actual DNA samples hail from Greenland (the icy one, as opposed to Iceland, the green one), extracted from beneath a mile of ice, a “perfect, natural freezer” for DNA preservation. The 450,000 to 800,000-year-old samples provide evidence of green life on the now largely barren landmass.

As far as human genetic material goes, the record for oldest Neanderthal DNA is held by a 100,000-year-old sample found in a Belgian cave. The longest-lasting sample of human DNA was discovered in northeastern Spain, and boasts a survival age of 7000 years. In both cases, techniques pioneered by Dr. Rhonda Roby allowed researchers to use mitochondrial DNA rather than the type found in the cell nucleus; although mitochondrial DNA only contains only partial genetic information, it provides sufficient evidence for identification and is present in greater abundance than nuclear DNA, increasing its odds of surviving.

How long does DNA last? The short answer is that it’s complicated, and determined by a number of unpredictable factors such as weather and the organism’s final resting place. Your DNA may be the molecular legacy you leave behind, but once you’re dead, there’s not really much you can do about it.

Original image
iStock
arrow
Big Questions
What's the Difference Between Vanilla and French Vanilla Ice Cream?
Original image
iStock

While you’re browsing the ice cream aisle, you may find yourself wondering, “What’s so French about French vanilla?” The name may sound a little fancier than just plain ol’ “vanilla,” but it has nothing to do with the origin of the vanilla itself. (Vanilla is a tropical plant that grows near the equator.)

The difference comes down to eggs, as The Kitchn explains. You may have already noticed that French vanilla ice cream tends to have a slightly yellow coloring, while plain vanilla ice cream is more white. That’s because the base of French vanilla ice cream has egg yolks added to it.

The eggs give French vanilla ice cream both a smoother consistency and that subtle yellow color. The taste is a little richer and a little more complex than a regular vanilla, which is made with just milk and cream and is sometimes called “Philadelphia-style vanilla” ice cream.

In an interview with NPR’s All Things Considered in 2010—when Baskin-Robbins decided to eliminate French Vanilla from its ice cream lineup—ice cream industry consultant Bruce Tharp noted that French vanilla ice cream may date back to at least colonial times, when Thomas Jefferson and George Washington both used ice cream recipes that included egg yolks.

Jefferson likely acquired his taste for ice cream during the time he spent in France, and served it to his White House guests several times. His family’s ice cream recipe—which calls for six egg yolks per quart of cream—seems to have originated with his French butler.

But everyone already knew to trust the French with their dairy products, right?

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Original image
NASA/JPL-Caltech/Space Science Institute
arrow
Big Questions
How Many Rings Does Saturn Have?
Original image
NASA/JPL-Caltech/Space Science Institute

Of all the planets surrounded by rings, Saturn is the most famous. These planetary rings are massive enough that Galileo was able to see them using a simple telescope way back in 1610, though it wasn't until half a century later that another scientist was able to figure out what the "arms" Galileo saw actually were. NASA has since called them "the most recognized characteristic of any world in our solar system."

So how many rings does Saturn have, anyway? If you can see them from your backyard, there must be a lot, right?

Scientists don't know for sure exactly how many rings Saturn has. There are eight main, named ring groups that stretch across 175,000 miles, but there are far more than eight rings. These systems are named with letters of the alphabet, in order of their discovery. (Astronomers have known about ring groups A, B, and C since the 17th century, while others are newer discoveries. (The most recent was just discovered in 2009.)

The rings we can see in images of the planet—even high-resolution images—aren't single rings, per se, but are in fact comprised of thousands of smaller ringlets and can differ a lot in appearance, showing irregular ripples, kinks, and spokes. The chunky particles of ice that make up Saturn's rings vary in size from as small as a speck of dust to as large as a mountain.

While the gaps between Saturn's rings are small, the 26-mile-wide Keeler Gap is large enough to contain multiple moons, albeit very small ones. The largest ring system—the one discovered in 2009—starts 3.7 million miles away from Saturn itself and its material extends another 7.4 million miles out, though it's nearly invisible without the help of an infrared camera.

Researchers are still discovering new rings as well as new insights into the features of Saturn's already-known ring systems. In the early 1980s, NASA's Voyager missions took the first high-resolution images of Saturn and its rings, revealing previously unknown kinks in one of the narrower rings, known as the F ring. In 1997, NASA sent the Cassini orbiter to continue the space agency's study of the ringed planet, leading to the discovery of new rings, so faint that they remained unknown until Cassini's arrival in 2006. Before Cassini is sent to burn up in Saturn's atmosphere in September 2017, it's taking 22 dives through the space between the planet and its rings, bringing back new, up-close revelations about the ring system before the spacecraft dives to its death.

Though it's certainly possible to see Saturn's rings without any fancy equipment, using a low-end telescope at your house, that doesn't mean you always can. It depends on the way the planet is tilted; if you're looking at the rings edge-on, they may look like a flat line or, depending on the magnification, you might not be able to see them at all. However, 2017 happens to be a good year to see the sixth planet, so you're in luck.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

SECTIONS

More from mental floss studios