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NOVA ScienceNOW

Trapped in Salt

  • By Rachel VanCott
  • Posted 04.01.09
  • NOVA scienceNOW

Scientists have discovered water-filled air bubbles trapped in salt crystals that are fully a quarter billion years old. In this audio slide show, biophysicist Jack Griffith describes ancient cellulose fibers and even DNA that he's found within such bubbles using an electron microscope. The material, he claims, is the oldest biological material ever discovered.

Launch Interactive

Biophysicist Jack Griffith takes you on a narrated photo tour of quarter-billion-year-old water bubbles.

Transcript

Trapped in Salt

Posted: April 1, 2009

JACK GRIFFITH: I'm Jack Griffith. I'm a professor of microbiology and biochemistry at the University of North Carolina in Chapel Hill.

This photograph, to the unexperienced eye [sic], looks like a lake that is partially frozen. You'd think this is ice and open water, but actually this is a salt lake on the surface above the Salado deposit in southern New Mexico. And the white material is solid sodium chloride, or halite salt, that is slowly crystallizing, and the Salado deposit is way underground, a half mile below. You have to go through a half mile of rock and then a half mile of solid salt in the Salado layer. And so that is where we go, going straight down through the 2000 feet of rock into the middle of the Salado deposit. And in this photograph I'm actually a half a mile under the ground, and I'm holding two salt crystals that we have collected for examination in our laboratory back in Chapel Hill.

Our goal was to see what might be present in tiny liquid droplets that are trapped within these salt crystals because these droplets are time capsules from a quarter of a billion years ago.

Several years ago, I believe the year 2000, a biologist, Russ Reland, and a geologist, Dennis Powers, and their colleagues took samples of the halite material and carried out some experiments that suggested that there might be the very rare occasional bacterium trapped in the salt material. In this photo Dennis Powers is using the light from his headlamp to illuminate an area on the salt wall where he thinks there might be crystals that would be good to look at in the laboratory.

This is a photograph of Sam Dominguez, who spends much of his life under the ground helping out and working with the geologists and physicists in the study of halite. And he is able to drill into the wall and then pull out a piece of salt that looks somewhat like a bagel. Round, flat, with a hole in the middle. And those are useful for us to look at.

In addition we carry geologist hammers and picks and often we will find salt crystals near the surface that we can collect simply by chopping and picking and prying them out.

This is a very low-power light microscope photograph of a solid piece of sodium chloride that has no discernable cracks in it, and so it's just one large, somewhat irregular-shaped crystal. It's perhaps the size of the average dog's paw. Two things immediately stand out when you look at it, and these are very small circular little, almost like little eyes, little round things with white centers.

Those are air droplets, so if you look more carefully, you see that each of those round air droplets is inside a rectangular cavity, and this regular cavity is full of fluid, and we've been particularly interested in pulling the liquid itself out and examining that in an electron microscope.

And for that process we have to drill into the crystal with a very tiny drill. In this photograph, we see one of the primary halite crystals being held in a clamp, and you can see above it—somewhat out of focus—a tiny 20 mil—that's twenty thousandths of an inch—steel drill. Then you slowly lower the drill, which is spinning at fairly low RPM, you don't want it to be shredding things too much, and then just at the moment when the drill penetrates into the liquid pocket, you quickly lift it out, and then we remove the liquid. Our current method is to use very thin glass capillary tubes.

This one is a little smaller, a bit bigger than an almond. You can very clearly see in the center a pocket, and this pocket has been drilled out, and I've inserted a very thin 22-gauge needle through the drill hole down into the pocket. This was our original way of removing the liquid, but it's not very efficient.

This is me in the lab with Smaranda Willcox, my research associate. We are standing in front of one of the two electron microscopes we have in Chapel Hill.

This electron microscope magnifies about 500,000 times. Costs a million dollars. It has numerous television cameras for collecting the images. The sample is placed on a tiny three-millimeter-diameter copper screen covered over by a very thin support. And then following our preparative steps that is placed on the end of a rod, and that is what Smaranda is doing in this photograph. She is placing the sample on the end of the rod, which will then be moved through an air lock into the center of the electron microscope.

When we first started viewing the samples we saw fields and fields of material that we did not know what it was, and the fibers were very small, they were quite stiff. In this image you can see two large, very big, clumps of the material, and then spewing out of that are ropes of these fibers of all different sizes.

We looked at the ropy material at higher and higher resolution, and they had dimensions typical of fibers that had been seen by other scientists and had been identified as cellulose fibers.

This is a magnification of the area from one of the last micrographs where you can see this angel-hair-pasta-like fibers even more clearly. The dimensions of these thinnest fibers is five nanometers, and that is known to be the size of the finest filament of cellulose. This ancient material was very likely ancient cellulose.

This may not look like cellulose, but it's what's left over when we treated the ancient fibers with an enzyme called cellulase. So when we took small amounts of this enzyme and mixed it with our ancient fibers, all that was left when we looked in the electron microscope were these little bits and pieces. This was the key experiment that defined our material as ancient cellulose.

When we looked at these samples on rather rare occasions in the background were clear examples of DNA molecules. We were rather surprised that there was DNA there because physical studies had indicated that DNA should not last as long as a quarter of a billion years. On the other hand, the high salt that is present in the liquid and also the fact that it is 2,000 feet beneath the surface and shielded from cosmic rays could be playing a great role in protecting DNA molecules.

This ancient DNA is 11,000 base pairs long. It could contain perhaps one or two genes worth of information. Occasionally we could find DNAs that were even longer than the 11-kilobase DNA. This one is perhaps twenty or thirty thousand base pairs in length.

It has been very useful to compare ancient and modern material. The modern material contains obviously much more biological material. In this image we see a bacterial cell that very likely grew in the high salt environment, and so when we washed it with water, the bacteria ruptured, spilling its insides out. And so this long, hotdog-like structure is the dense bacterium, and then the kind fluffy stuff on either side of it is other material that was inside the bacterium. In the background then are more cellulose fibers, looking identical to what we had seen in the ancient material.

Now the modern fibers have little bumps and blips on them, material that was present initially on the sample trapped in the salt, but over a quarter of a billion years that material would apparently dissolve and disappear. So by comparing modern and ancient we can see what sort of material may survive the quarter of a billion year trip.

Of the perhaps thousands of images we have collected, the low magnification fields of the cellulose fields are the most striking. They're not only beautiful in an artistic sense, but the fibers are highly regular, they're twisted, they're very interesting in the way they're put together. So they're really no different from normal cellulose produced in nature today, and yet they're a quarter of a billion years old, so this is the oldest biological material, intact biological material, ever discovered on the planet by about 200 million years.

Credits

Audio

Produced by
Rachel VanCott

Images

(all)
© Courtesy Jack Griffith

Related Links

  • Secrets in the Salt

    Salt deposits that formed 250 million years ago hold tantalizing hints of early life.

  • Secrets in the Salt: Expert Q&A

    Jack Griffith answers questions about cellulose, DNA, and other organic bits found in Permian salt deposits.

  • Martian Salt

    If cellulose survived 250 million years on Earth, could it survive in salt deposits on Mars?

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