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How does amber form?

Updated: 7 days ago

How does amber form?

Amber starts off its life millions of years ago as a sticky type of sap exuded by a tree, called pitch. Pitch is similar to sap, but more sticky, and if an insect lands on the pitch it will be trapped forever. You can still find pitch on trees today, like on the cherry tree pictured below.


Fresh pitch on a cherry tree that will become amber
Fresh pitch on a cherry tree - This is an example of how pitch forms. You may have seen something similar in real life. You can see a leaf stuck to the pitch on the left side. This is the first stage of amber.

The Amber forms out of trees like in the diagram below. During this process in insects can become stuck in the Amber. Read this For more information about how insects get stuck in Amber.


Diagram of amber forming in a tree
How amber forms - When a tree is damaged in any way, it produces pitch. Pitch comes out slowly and progresses over time. Eventually, very large globs of pitch can form which will later turn into large pieces of amber

When this pitch is buried underground for millions of years, it gradually hardens and fossilizes into amber!



Why do trees produce resin, and what is it made of?

Amber isn't fossilized tree sap, it's fossilized pitch. Pitch is sap that has dried and concentrated, becoming much thicker and stickier. Trees produce pitch to defend itself against insects and disease. So how does a tree defend itself against a beetle boring into it? It produces pitch, which goops out of the beetle's bore hole. And it covers up the beetle in the process, preserving it perfectly.


Fresh pitch oozing out of a cherry tree
Cherry Tree Pitch - This cherry tree was attacked by beetles, and each bore hole produced fresh pitch. This pitch can capture insects that it touches, and will eventually fossilize into amber if the conditions are right.

Resin production is often related to insect attacks, but it can also result from forest fires burning trees, high winds breaking branches, and even animal damage to the trees. The resin serves both to protect from creatures as well as from diseases like fungal infections.



How do insects get stuck in amber?

Pitch is very sticky when fresh on a tree. It is a very similar consistency to honey. Therefore, any insect that lands on the pitch is likely to get stuck. The pitch runs down the trees, so in it's path it can run over insects and lift them into the resin flow, trapping them. Sometimes, pockets of resin can build up inside a tree and burst violently. When that happens, the resin can capture even large creatures in it's path like lizards or birds. And in the case of Burmese amber, possibly even dinosaurs. Other things can get captured in amber too, like plants, flowers, mushrooms, seeds, and more. These fossils help scientists assemble the biota of ancient forests, which expands our fossil record.


Diagram showing how a mosquito gets trapped in Amber
How A Mosquito Gets Stuck in Amber - The mosquito is attracted to the pitch because of it's sweet smell. When it lands on the pitch, it gets stuck. More pitch flows over the mosquito, entrapping it. Even more flows over, making it buried deep inside golden amber.
Mosquito and Amber held in a hand
A Mosquito in Amber - The end result of the mosquito getting trapped in amber.
Lots of insects in Amber being held in hand
Dominican Amber with Wasps - A clear yellow piece of Dominican amber that has a swarm of clear wasps preserved inside. This is a museum-grade piece.

How does the amber get preserved for millions of years?

Some ancient trees produced a lot more resin that modern trees. Imagine a forest full of trees producing large globs of resin. Those globs of resin are what will eventually become amber. Now a river that runs through that forest will collect falling trees and their globs of amber. Amber is buoyant and easily carried downstream. Those streams lead into lagoons or river deltas, where the trees and their ambers collected. These places eventually became large deposits of amber. The earth covered them up, and they end up underground for millions of years. Being underground protects them from the elements, and they stay perfectly preserved for all this time. Therefore a rich amber deposit is a combination of fortuitous factors involving concentration of the amber, appropriate burial, as well as a nearby forest that produced large quantities of the right kind of resin.


Diagram of how Amber deposits are formed
How Amber Deposits Form - A forest of trees produce resin. The dead trees and their resins fall into nearby rivers. When the trees float downstream, they become deposited in lakes and estuaries, where they aggregate and form a concentrated deposit. Over time, the resins become amber and the trees become lignite.


Do any trees still produce as much resin as in prehistoric times? Yes, some living trees still produce very large amounts of resin that could become amber in millions of years. Most notably is the Kuari tree in New Zealand, famous for it's resinous output of "Kuari Gum," a type of copal.

Large kauri tree
The Kauri Tree - This tree produces massive amounts of resin to this day. The resin is called “Kauri Gum,” and is technically copal. This is the same species of tree that produced Burmese amber 100 Million Years Ago.

In fact the ancient forests that produced Burmese amber were mostly made of Kuari Gum trees. Also the Ponderosa Pine produces massive flows of resin when bark beetles chew galleries into the wood. Cherry Trees also produce notable amounts of resin that can be collected by hand.

Large glob of pitch hanging off a kauri tree
Large Fresh Pitch on the Kauri Tree - This is what amber production would have looked like in the time of the dinosaurs. And with a whole forest of these trees, it would have been a very sticky world with lots of insects getting stuck.

So remember next time you see a sticky golden substance dripping down a tree. If you bury it and come back in 100 Million years, it will be amber!


Sources:

Zheng, Daran, et al. “A Late Cretaceous Amber Biota from Central Myanmar.” Nature Communications, vol. 9, article 3170, 2018, https://doi.org/10.1038/s41467-018-05650-2







 
 
 

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