What are Two Different Ways that Fossils Form?

What are Two Different Ways that Fossils Form?
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Amber and Fossilized Shark Teeth Are Often Found on Beaches

What are two different ways that fossils form? Fossils can form in a number of ways; they have in common that it takes several million years. Here we describe permineralization and how organisms are captured in amber. You can be lucky and find amber on beaches where it is washed ashore after it has been in the sea for millions of years. Amber is often used for jewelry. Permineralization is the process that turns bones, teeth and wood into fossils. Petrified wood is an example of this process, and so are shark teeth, which you can also be lucky to find on beaches.

Permineralization Fills out Pores With Minerals

During permineralization minerals such as silica, calcite or iron are deposited into porous tissue, such

Valdosaurus nigeriensis

as bones, teeth or wood. It can preserve both hard and soft body parts. The minerals fill out the internal structures and the cells of the organism. Permineralization produces fossils that contain both original organic material and the minerals. The fossils can remain for many millions of years deep underground until the layers they are in are pushed closer to the surface and they are exposed by weathering.

Here is a step by step process of how fossils form by permineralization:

  1. An organism dies and is buried in water.

  2. Sediments bury the organism. This can happen fast with landslides.

  3. Water containing dissolved minerals infiltrates the pores in the bone or wood and deposits the minerals in the pores and cellular spaces.

  4. Many layers are formed and eventually fill out all the bone or wood.

  5. Sediments continue to pile on top of the bone or wood, and as they pile up, they put pressure on the lower layers creating a hard

    petrified wood


Examples of permineralized fossils include dinosaur bones, shark teeth, many marine invertebrates, trilobites and plants. Permineralized fossils are found from all the Geological Time Periods.

The organic material can later be replaced with minerals turning the whole bone or piece of wood into stone - this process is called petrification. This process commonly happens in wood, and examples of this are the petrified forests found in Namibia, California, Mississippi, Arizona and Washington.

Preservation of Organisms in Amber

Amber formation is a very different way that fossils form. Amber is also called fossil resin. The resin is excreted from pine trees and buried under sediments, and over time, polymerization takes place and hardens the resin.

Insects in baltic amber

Amber is in itself a plant fossil, but even more interesting is when organisms are trapped inside the amber. Fossilized organisms found in amber include insects, spiders, plants, fungi, bacteria and even small geckos.

Here is the step by step process of how amber fossils form:

  1. Resin is produced by coniferous trees as a defense mechanism or to heal holes. Essential oils compose most of the resin.
  2. Resin flows down the tree and traps animals, bacteria or plant material.
  3. Polymerization changes the structure of the resin and hardens it. This stage is called copal.
  4. The concentration of essential oil decreases and the polymerization continues.
  5. After million of years, it hardens into amber.

Amber is up to 300 million years old, the Carboniferous Period, though most are from the Jurassic Period or younger, 140 million years ago.

Mosquito in amber

Amber is so interesting because it preserves whole organisms including the soft tissues, and sometimes it can preserve a whole ecosystem by entrapping animals, plants and bacteria at the same time. It is possible to extract and sequence DNA from preserved species, but there will rarely be enough to replicate the organism.

The majority of amber is found in the Baltic Sea Region from pine trees in Russia. They wash ashore on beaches in Germany, Poland, Lithuania, Denmark, the former Soviet Union, Great Britain, Estonia, Latvia, and Holland. Amber is also found in Colombia.

Fossil Formation Is a Long Process

Permineralization and amber formation are two very different ways that fossils form. These two processes have in common that it takes million of years before the organism becomes a fossil. They are very different in the way that permineralization turns a bone, wood or teeth into a fossil from the inside out while resin traps and encapsulates a whole organism. Both kinds of fossils provide valuable insight about the fossil record and help us understand how life forms have evolved.

Now that you know the answer to the question: “what are two different ways that fossils form?” you may be curious to learn about other ways that fossils form. You can see permineralization and other ways of fossil formation in this video from FlashYourBrain: how do fossils form in animation.


Anderson, K., et al. In Amber, Resinite, and Fossil Resins; ACS Symposium Series; American Chemical Society: Washington, DC, 1996. https://pubs.acs.org/doi/pdf/10.1021/bk-1995-0617.pr001

Butterfield N. J. “Exceptional Fossil Preservation and the Cambrian Explosion.” Integrative and Comparative Biology. Volume43, Issue1. Pp. 166-177. 2003. https://icb.oxfordjournals.org/content/43/1/166.full

Oregon State University (2008, September 3). “Oldest Gecko Fossil Ever Found, Entombed In Amber”. ScienceDaily. Retrieved February 24, 2011, from https://www.sciencedaily.com­ /releases/2008/09/080902163920.htm

The Virtual Fossilmuseum: https://www.fossilmuseum.net/fossilrecord/fossilization/fossilization.htm and https://www.fossilmuseum.net/Tree_of_Life/FossilAmber.htm

University of Florida (2007, October 20). “How Amber Becomes Death Trap For Watery Creatures.” ScienceDaily. Retrieved February 24, 2011, from https://www.sciencedaily.com­ /releases/2007/10/071018123512.htm

University of California Museum of Paleontology: https://www.ucmp.berkeley.edu/paleo/fossils/permin.html and https://www.ucmp.berkeley.edu/paleo/fossils/amber.html

Image Credits

Dinosaur Bone: Wikimedia Commons/Ghedo

Shark Tooth: Wikimedia Commons/Chmee2

Mosquito: Wikimedia Commons/Mila Zinkova

Insects in Baltic Amber: Wikimedia Commons/ Mila Zinkova

Bee: Wikimedia Commons/ Michael S. Engel

Petrified Wood: Image provided by writer.

This post is part of the series: All About Fossils

This article series focuses on fossils. It includes a guide to the major groups of fossils, explores which fossils are found in the deserts around the world, describes how deep sea fossils are used to shed light on evolutionary events, explains the fossil record, and describes how fossils are formed

  1. A Guide to the Major Groups of Fossils
  2. Paleontologists Define Fossil Records as all the Fossils Found on Our Planet
  3. Two Ways in Which Fossils Form: Permineralization and Amber
  4. What Kind of Fossils are Found in the Desert?
  5. Fossils in the Oceans Document Mass Extinctions and Climate Changes