​How amber creates exquisite fossils

For many thousands of years, the fossilized tree resin known as amber has entranced jewelry makers and inspired the scientific imagination. For the past 200 years especially, paleontologists around the world have turned to amber to understand the ancient past—by studying the amazing fossils preserved within it. 

Have questions about amber? We’ve got you covered.

What is amber, and how do fossil inclusions end up within it?

Plants secrete many kinds of viscous liquids, such as latexes, gums, and waxes. Some kinds of plants, usually woody plants, produce resins: complex, sticky substances that don’t dissolve in water and harden when exposed to the air.

Resins serve to scab over plants’ wounds, making them sort of like the platelets in our bloodstream. When a plant that makes resin gets injured or otherwise has a break in its surface—such as a crack running down a tree’s bark—resin oozes out of the area. As the resin sits out in air and bakes in sunlight, it starts to harden. This process forms a protective cover over the plant’s wound, helping to keep out fungi and other pathogens.

Because resin is sticky, small creatures can get stuck in it as it oozes over trees’ bark, drips onto the ground, or even flows out of trees’ roots. On occasion, some of these globs end up in water: perhaps because a tree happened to be growing on the shore of an ocean or lake, or maybe because a flood swept the tree into a river. Of these waterborne globs of resin, some end up buried within sediment, such as the sand of a floodplain or the silt at the bottom of a lake.

The deeper the resin gets buried over many millennia, the more pressure and heat the resin will end up feeling. Over an extended period, these conditions cause the resin’s compounds to polymerize, or chemically react with each other to form a thicket of molecular linkages. This process yields the hard, glassy material that we know as amber—and it also can preserve, with extraordinary fidelity, the shapes of any small creatures trapped within the amber.

How long does it take resin to form into amber?

It’s hard to say, exactly. Resin’s transformation into amber is ultimately a product of the conditions that the blob of resin has experienced. In general, though, amber is usually well more than 40,000 years old. Any younger than that, and the material has a good chance of being classified as copal, an old, polymerizing resin that still has some of the material properties of the fresh material, such as a tackier surface.

What kinds of fossils have been found in amber?

Because amber can envelop and protect even soft-bodied creatures, it’s great at preserving the tinier, squishier denizens within forest ecosystems. Over nearly two centuries, paleontologists studying amber have found insects, arachnids, crabs, plants, fungi, nematodes, plants, microorganisms, and even the occasional piece of a bigger vertebrate animal.

But as you might imagine, the fossils that end up in amber are skewed toward the creatures that would have had a higher chance of getting entombed within an ancient tree’s resin.

Where are fossils in amber found?

There are more than 160 sites around the world where copal or amber have been found, and the oldest amber on Earth—found in an Illinois coal seam—is about 320 million years old. However, these blebs of amber are less than a quarter of an inch wide on average, and they don’t have any fossils inside them. Of Earth’s total amber deposits, only a few dozen or so yield a wide array of fossils. Nearly all of these fossil-bearing deposits are about 125 million years old and younger, with one known exception: a 230-million-year-old amber deposit in the Italian Alps that preserves a species of fly and two species of mite.

What are some of the best-studied amber deposits in the world?

Baltic amber is usually estimated to be between 34 million and 38 million years old, though some deposits formed earlier. It erodes out of sediments along the shore of northern Europe’s Baltic Sea, with the best-studied deposits coming from what’s now Kaliningrad Oblast, Russia. More than 3,500 species of fossil arthropods have been found in Baltic amber, including more than 650 species of spider. Rarely, Baltic amber yields vertebrate fossils—including a spectacular gecko, named Yantarogekko balticus, dated to around 54 million years old. It’s also yielded fossils of plants, including the biggest known fossil of a flower preserved in amber.

Dominican amber is generally thought to be between 15 and 20 million years old, though its exact age is a matter of debate. Scientists have found more than 1,000 fossil species within its amber, including more than 400 species of insect and 150 species of spider. Occasionally vertebrate fossils also pop up, including anoles and even a salamander.

Burmese amber is about 99 million years old, and it comes from mines in northern Myanmar’s Kachin state, which have been exploited for the jewelry trade for roughly the past 2,000 years. Scientific interest in Burmese amber has surged over the past two decades, as paleontologists have uncovered an extremely diverse ecosystem: carnivorous “hell ants” entombed mid-meal, the partial tail of a feathered dinosaur, the shell of a marine creature known as an ammonite, and even an ancient baby bird.

However, paleontologists are also hotly debating the ethics of studying Burmese amber. Kachin’s amber mines have been at the center of decades of conflict between Myanmar’s military and local independence groups, and few recent scientific studies of Burmese amber have included co-authors from Myanmar.

Canadian amber is between 78 million and 79 million years old, and it primarily comes from a site called Grassy Lake in the western province of Alberta. More than 130 different fossil species have been found within amber here, many of which are aphids or mites. But some pieces of amber include bits of conifer needles, fungi, pollen, and even feathers from birds and other dinosaurs.