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Fossils encompass a variety of natural remnants, such as this trilobite fossil from the Green River Formation in Wyoming. Layne Kennedy / Getty ImagesFossils refer to diverse natural evidence of ancient plant and animal life, conserved within the Earth's crust.
When discussing fossils, most people refer to a specific category where the structure of the organism remains intact, but its organic material has vanished. So, how are fossils created, and what insights do they provide into Earth's distant past?
Understanding Fossils: A Quick Primer
At its core, a fossil represents the conserved remnants or imprints of organisms that once inhabited Earth. Fossils extend beyond dinosaur bones or ancient flora; they can also include footprints, trails, or even fossilized excrement, known as coprolite.
Types of Fossils
- Body fossils: These are the most commonly recognized type of fossils, encompassing the preserved remains of ancient animals and plants, such as dinosaur bones or fossilized leaves.
- Trace fossils: These are not the actual organism but evidence of its presence, including footprints, burrows, or fossilized droppings.
With a clear understanding of what fossils are, let’s explore the fascinating process behind their formation.
The Making of a Fossil
- An animal dies. This is the first step in the fossilization process. When an animal perishes and is swiftly covered by sediment, such as mud or sand, the conditions for preservation are set. Quick burial is crucial for safeguarding harder body parts like bones or shells. Soft-bodied organisms, however, rarely fossilize due to their fragile nature.
- Sediment layers build up. Over millions of years, layers of sediment accumulate over the buried remains, eventually compacting into solid rock.
- Nature plays its part. Groundwater infiltrates the sediment, depositing minerals into the pores and cavities of the remains. As the organic material decays, it leaves behind a natural mold. Minerals like calcium carbonate fill this mold, creating a cast fossil.
- The fossil forms. Over time, erosion or human activity may uncover these rocks, revealing the ancient preserved remains.
A fossil of a Microraptor from a 130-million-year-old forest in what is now Liaoning Province, China, is exhibited at the American Museum of Natural History in New York City.
Getty ImagesNature's Treasure Chest: Unique Fossil-forming Processes
Fossil formation isn't confined to sedimentary rock processes. Nature employs a variety of methods to create these ancient treasures.
- Amber: Certain ancient insects met their fate by becoming ensnared in tree sap, which, over millions of years, hardened into amber.
- Petrified wood: Minerals gradually infiltrated fallen trees, replacing their organic material cell by cell, maintaining their structure while transforming them into stone.
- Tar pits and other sticky situations: Animals occasionally became trapped in tar pits, bogs, or quicksand, resulting in exceptional preservation. Volcanic ash has also contributed to fossil preservation, particularly for terrestrial creatures.
Why Should We Care About Fossils?
Fossils reveal the types of plants and animals that lived in prehistoric eras and offer insights into their environments, behaviors, and interactions. The fossil record — the global collection of all fossils — acts as a historical archive of Earth's past.
Moreover, through methods like carbon dating, paleontologists can estimate the age of fossils, aiding in the reconstruction of life's timeline on Earth. This helps determine which species coexisted and which existed earlier.
Fossil Fun Facts
Most Organisms Don't Become Fossils
In reality, fossilization is an exceptionally rare occurrence. Rapid burial is essential, and the environmental conditions must be precisely suitable.
Not All 'Fossils' Are Ancient
Some fossils may be only a few thousand years old, while others, especially those of marine creatures preserved in sedimentary rocks, can be over 500 million years old.
The Jurassic Period Rules
When imagining dinosaur fossils, the Jurassic period often comes to mind, as it was a flourishing era for these colossal reptiles.
