Fossil

A fossil is any preserved remains, impression, or trace of a living thing from a past geological age. This can include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, and even DNA remnants. The study of fossils, called paleontology, helps scientists understand how life on Earth has changed over millions of years.

Fossils can vary greatly in size, from tiny one-micrometre bacteria to huge dinosaurs and trees. They provide important clues about the history of life, showing how different species evolved and lived together. By studying where fossils are found and their age, scientists have been able to create a geological timescale that helps us understand the order in which events happened in Earth's past.

Many processes can lead to the formation of fossils, including permineralization, casts and molds, and carbonization. Fossils are not always the actual remains of an organism; sometimes they are marks left behind, such as animal tracks or feces known as coprolites. These are called trace fossils or ichnofossils, and they give scientists valuable information about how ancient animals lived and behaved.

History of study

Main article: History of paleontology

For a chronological guide, see Timeline of paleontology.

People have found and studied fossils for thousands of years. Fossils help us learn how life on Earth has changed. They are important for understanding evolution. Paleontologists study fossils to see how species have changed over time.

Long ago, people used fossils in many ways. For example, some early humans in Europe used fossil shells to make jewelry. The ancient Egyptians kept fossils that looked like animal bones in their temples. In China, fossils were sometimes thought to be dragon bones and used for medicine.

As time went on, people learned more about fossils. Scientists like Aristotle discovered that fossils in rocks were actually old sea creatures. Scholars used fossils to learn about Earth's history and its living things. Today, fossils are still important for learning about the history of life on our planet.

Dating/Age

Main articles: Geochronology and Relative dating

Fossils help scientists learn about life from long ago. But finding out exactly how old they are can be hard. One way to find the age of rocks is called radiometric dating. It measures how some elements change over time. This works best for rocks older than 50 million years, like volcanic ash.

Scientists also use a method called stratigraphy. This looks at layers of rock. Newer layers are on top of older ones. Fossils found between dated layers can give clues about their age. Special fossils, called index fossils, lived for short times and are found all over the world. They help match rock layers from different places. But dating fossils is not always simple, especially if the rock layers are broken or worn away.

The fossil record is not complete. Only a few organisms become fossils. Most fossils are from animals with hard shells or bones. Creatures with soft bodies are rarely preserved. This means we are missing many parts of the story of ancient life.

Sites

Main article: Lagerstätte

Further information: List of fossil sites

Some fossil sites are special because they show us amazing details about ancient life. These sites are called Lagerstätten, which means "storage places" in German. They form when animals are buried quickly, helping keep their remains safe. Examples include the Cambrian Maotianshan Shales and Burgess Shale, the Devonian Hunsrück Slates, the Jurassic Solnhofen Limestone, and the Carboniferous Mazon Creek areas. Scientists can learn a lot from these places.

Fossilization processes

Fossilization is how parts of living things get trapped in rock over time. One way this happens is through recrystallization. This is when materials like shell change into different crystal shapes, such as from aragonite to calcite.

Another process is replacement. This is when the original material of a shell or bone gets swapped out for minerals. This can save very tiny details of the old organism. Permineralization is a special kind of replacement. Minerals fill the empty spaces inside the organism, making very detailed fossils. Other replacement ways include phosphatization, where organic matter turns into dark minerals, and pyritization, where sulfur and iron create a fossil using pyrite.

Casts and molds happen when the original organism dissolves away, leaving a shape in the rock. If this space later gets filled with sediment, it makes a cast that looks like the original organism. Adpression means fossils made by compression, where the remains get flattened but still show details of the original organism. Some fossils can even save soft parts or tiny cell structures, which is rare but has been found in some dinosaur fossils.

Types

Index

Main article: Index fossil

Index fossils help us find out about old times in Earth’s history. They work because different layers of rock can have the same species of fossil. The shorter the time a species lived, the better these fossils can help match different rock layers. Species that changed quickly are especially useful as index fossils.

Trace

Main article: Trace fossil

Trace fossils show clues about ancient life through tracks, burrows, and other marks, not the actual remains of the animals. They are important because they show what animals were doing and can go back further in time than fossils of their bodies.

Transitional

Main article: Transitional fossil

Further information: List of transitional fossils

Transitional fossils show features from both an older group of animals and the group that came after them. They help us remember that groups of animals are labels we use, and that all life changes gradually over time.

Microfossils

Main article: Microfossil

See also: Micropaleontology and Protists in the fossil record

Microfossils are very small fossils that you can only see with a microscope. They include tiny organisms or parts of bigger ones, like teeth or spores. Microfossils help scientists learn about past climates and are used to figure out the age of rock layers.

Resin

Main article: Amber

Fossil resin, called amber, is a natural polymer that can trap and preserve tiny creatures. These trapped fossils, called inclusions, can include insects, spiders, and even small pieces of DNA. They give scientists a close look at life from long ago.

Derived or reworked

See also: Zombie taxon

Derived or reworked fossils are fossils that were formed long ago but were moved and placed in newer rock layers by natural forces like wind or water.

Wood

Fossil wood is wood that has been preserved in the fossil record. It can become stone, a process called petrification, or it can stay as wood. Petrified wood often shows details like growth rings.

Subfossil

The term subfossil describes remains that are not fully turned into fossils. These can be bones or shells that are thousands of years old but not old enough to be true fossils. Subfossils can still have organic material that helps scientists study past environments and climates.

Chemical fossils

See also: Biosignature

Chemical fossils are chemicals found in rocks that show signs of ancient life. These include certain molecules and isotope ratios. Some of the earliest proof that life existed on Earth comes from chemical fossils.

Stromatolites

Main article: Stromatolite

Further information: Earliest known life forms

Stromatolites are layered structures made in shallow water by very small organisms, especially cyanobacteria. They trap and bind bits of sediment. Stromatolites are some of the oldest fossils we know, dating back more than 3.5 billion years.

These structures tell us about the first life on Earth.

Stromatolites were more common in the past, before complex animals appeared. Their numbers dropped when grazing animals began to eat them. This shows that more advanced life developed over a billion years ago. Today, similar structures can still be found in some places. They help scientists learn about how life began and changed on our planet.

Pseudofossils

Main article: Pseudofossils

Pseudofossils are patterns in rocks that look like fossils but are made by nature, not by living things. For example, some pseudofossils, like geological dendrite crystals, form when cracks in rocks fill with minerals. Others, such as kidney ore or moss agates, might look like round shapes or plant leaves. Concretions, round nodules found in layers of sediment, were once thought to be dinosaur eggs but are really just natural rock formations.

Astrobiology

Scientists think that special minerals made by living things could help us find life beyond Earth, especially on planets like Mars. These minerals and other signs of life are called biosignatures. They are important for understanding how life might start and grow.

In 2014, NASA sent robots called Curiosity and Opportunity to Mars. The robots looked for clues about past life. They searched for signs of tiny living things and places where water once existed. Finding these clues helps scientists learn if Mars ever had or still has life.

Art

Some very old pieces of art may show fossils. One idea is that a vase from long ago might show a fossil, but another study says this is not correct. The shape on the vase looks more like a type of lizard that people in ancient times would have known about.

Trading and collecting

Fossil trading is when people buy and sell fossils. Sometimes this happens in ways that are not allowed, taking fossils from places where scientists study them. This can mean we lose important pieces that help us learn about the past.

Fossil collecting, or fossil hunting, is when people look for fossils. They do this to study them, have fun, or to sell them. Both experts and people who just enjoy it collect fossils because they help us understand life from long ago.

As medicine

Some cultures used fossils to help with health problems. They thought the fossil looked like the body part that needed healing. For example, dinosaur bones were called "dragon bones" and used in traditional medicine. These treatments might have made people feel better, but they did not really cure anything. Fossils may have given some minerals our bodies need.