How amber locks history in its golden tomb


These amber-entombed cockroaches were discovered in Lebanon. (From Peter Vrsansky/Geological Institute Slovak Academy of Sciences)
January 20

In the 1993 film “Jurassic Park,” miners discover a mosquito entombed in a red-yellow substance, supposedly carrying the DNA of long-extinct dinosaurs, waiting to be revived by modern scientists. It’s a dramatic moment, but as recent events have shown, amber’s real-life exploits are so much more interesting.

This month, a team of researchers in Oregon and Germany released a series of remarkable photographs of a 100-million-year-old flower frozen in the act of sexual reproduction in a piece of amber. This just after scientists released images of an ancient species of cockroach trapped in amber. In 2012, amber gave us a pair of 100-million-year-old spiders locked in combat.

How did these living things become encased in their golden tombs? If you don’t know, don’t be embarrassed. People have long misunderstood the magic of amber. In the ambitiously titled 1803 book “The Wonders of Nature and Art: or, A Concise Account of Whatever Is Most Curious and Remarkable in the World,” the author notes that the issue of how animals become locked in amber “is a question much agitated amongst the curious enquirers into the works of nature.” He goes on to dismiss speculation that amber is “of vegetable origin,” since animals only get stuck to the outside of such juice flows, not entombed within them.

In fact, that is exactly what happens. Amber begins as resin, a reddish, viscous liquid that flows out of a diseased or damaged tree. Several different types of trees are capable of producing the resin that becomes amber, but it’s usually one particular tree in each area where fossilized amber is abundant. In the Dominican Republic, for example, an extinct leguminous tree provided most of the resin responsible for the area’s 16-million-year-old amber fossils.

When an animal comes along — often an insect, but larger animals have occasionally become engulfed — it can get stuck in the resin flow. At first, it may be only a part of the animal caught in the resin, but several additional doses of resin can come flowing down, eventually submerging the trapped creature. This is why you can sometimes observe layers in a piece of fossilized amber. Not all amber specimens are layered, though. If the animal is small enough, and the flow of resin large enough, a single dose of resin may engulf the creature. These flash floods of resin produce the some of the best preserved fossils.

After the animal is caught, the resin begins to polymerize and harden. (The exact chemistry is not completely understood.) Perhaps the tree falls and becomes covered in other organic matter. If the pressure and temperature conditions are right, the resin transforms into the semi-fossilized substance copal. The speed of this process varies tremendously depending on the conditions. Scientists don’t agree on when resin officially becomes copal, or when copal officially becomes amber. Some say that amber must be at least 2 million years old, but that cutoff is arbitrary. (Copal is a notable substance, because fraudsters often peddle the substance as the older and far more valuable amber. If you’re ever considering dropping a large sum of money on fossilized amber that you suspect might be copal, apply a solution of ether to the surface. Amber does not react with ether, while copal will become sticky.)

Most true form fossils — the kind you typically see at a natural history museum — lack soft tissue. It wasn’t until 2005, for example, that paleontologists managed to detect the remains of blood cells buried deep within rock-solid, 68-million-year-old dinosaur fossils. Fossilized amber can be an exception, because it rapidly dehydrates an animal. In some cases, the process preserves soft tissue like the animal’s brain or other parts of the nervous system.

Many scientists have even reported extracting DNA from an ancient animal encased in amber, which brings us back to the “Jurassic Park” scenario. Steven Spielberg released his film at a time of great excitement among paleontologists. In the early 1990s, several researchers announced remarkable DNA recoveries from a variety of creatures preserved in amber, including bees and beetles, some of which were more than 100 million years old. The claims upended the conventional wisdom that DNA could not survive more than approximately 1 million years. It now appears, however, that the conventional wisdom was correct.

David Penney, a researcher at the University of Manchester, published a study in September 2013 showing that most of the DNA “finds” of the 1990s were, in fact, contaminants rather than true ancient DNA. “Some of those researchers have held up their hands and said it was probably contaminant DNA, but some still hold to their claims,” he notes.

The problem with the early studies was that the PCR sequencing technique used two decades ago preferentially detected long strains of DNA. Any modern DNA floating around the laboratory, therefore, was likely to be picked up and amplified. Next-generation methods are better at detecting ancient strands, which are likely to be small and broken-up. Using those methods, Penney’s team came up empty. Sorry, Spielberg fans.

Still, though we may not be on the verge of reviving dinosaurs, that doesn’t mean you should ignore the wonders that amber has brought us.

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