Fossil Formation and Uncovering the Ancient Past
How do we know that dinosaurs existed? Well, it’s not just from looking at their evolutionary descendant the chicken. Instead, the truth about ancient history and its dwellers lie in the discovery of a fossil. But, what is this scientific capsule? In today’s blog, we uncover the formation of these records. Plus, disclose how they reveal the history of the world.
What is a Fossil and How Does it Form?
A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include:
- bones
- shells
- exoskeletons
- stone imprints of animals of microbes
- objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants
Specimens are fossils if they are over 10,000 years old. In fact, the oldest dates to around 3.48 -4.1 billion years old. The process of dating these ages has evolved over the centuries thanks to advancements in technology.
The Fossilisation Process
The transformation varies according to tissue type and external factors.
- Permineralisation occurs when an organism is buried. The empty space within an organism fill with mineral-rich ground water. This allow for some specimens to contain traces of skin, feathers, or even soft tissues.
- Casts and moulds occur when the original remains completely dissolve or are otherwise destroyed. But, in it’s place, it leaves an organism-shape hole. Often, this void fills with a sediment to create a cast resembling what the organism looked like.
- Replacement occurs when another mineral replaces the shell, bone, or another tissue. Recrystallisation is when the original skeletal compounds are still present, but in a different crystal form.
- Compression is a result of the chemical reduction of the complex organic molecules. In many cases, compressions and impressions occur together.
- Preservation depends on the arrangement of certain fibres and molecules. For example, tight packing favours good preservation. Additionally, the alternation of an organism’s tissues by chemical reduction must have occurred.
- Carbonisation consists of the reduce organic remains to the chemical element carbon. It shows a think film which forms a silhouette of the original organism.
- Bioimmuration occurs when a skeletal organism overgrows and preserves another organism.
What They Tell Us About History
We now know how a fossil comes to be. But, how do scientists (specifically known as palaeontologists) use them to uncover the ancient past?
Types of Fossils
As we’ve discovered, a fossil appears in many different forms. But, what’s more, they also belong to different categories that reveal different information.
- Index. These specimens define and identify geologic periods. They work on the premise of spotting the same species of fossil despite the process of fossilisation.
- Trace. These specimens represent animal behaviours. They consist mainly of tracks and burrows, but also include marks left by feeding.
- Transitional. These reminds exhibit traits common to both an ancestral group and its derived descendant group.
- Microfossils. This terms applies to fossilised plants and animals who are no visible to the naked eye.
- Resin. Colloquially called amber, the hardening of this natural polymer traps bacteria, fungi, other plants, and animals for thousands and thousands of years.
- Subfossil. This type refers to remains whose process is not complete. They are often found in caves or another shelters because this allows them to be preserved for thousands of years. What’s more, these specimens contain organic material perfect for radiocarbon dating.
Dating
So, how do we go from a fossil discovered today to knowing when the fossilisation process occurred? Whilst radiometric dating is very exact, it cannot work on fossil beds that lack the necessary radioactive elements.
Instead, a process called stratigraphy reveals the age of the layers the specimen lies in. Thus, if a scientist knows the age of the two layers an organism lies in, then we know the specimen’s age lies between these two know ages.
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