The word fossil was once defined simply as “something dug up.” Today, it is understood to mean the preserved remains or trace evidence of prehistoric life. The scientific study of fossils is known as palaeontology, and a person who collects and studies fossils is called a palaeontologist. Fossils can range in size from microscopic grains of pollen or tiny seeds to enormous limb bones from giant dinosaurs.
For animal or plant remains to become fossilised, they must undergo specific processes that preserve them for millions of years after death. In most cases, only the hard parts of organisms—such as bones, teeth, shells, or wood—survive this long and complex journey to becoming a fossil.
Plant Remains
Hard seeds and woody structures are preserved far more commonly than flowers and leaves. While flowers and leaves themselves usually decay, they can leave behind thin carbon impressions that retain much of their fine detail, revealing the delicate structure of the original plant material.
Animal Remains
Teeth, bones, and shells are far more commonly found than the much rarer skin, flesh, fur, hair, or feathers. In most cases, only one or two bones and/or teeth are discovered at a time, and finding a complete skeleton is extremely rare.
On very rare occasions, entire mammoths have been discovered in places such as Alaska and Siberia, frozen solid for thousands of years. These so-called “frozen fossils” have preserved not only the bones and teeth, but sometimes the whole animal, including soft tissues.
Molluscs
Just as today we can collect seashells along beaches, the shells of marine animals also accumulated along riverbanks, beaches, and coastlines in prehistoric times. When the sea retreated, these shells were buried by layers of mud, silt, and sand. Over time, these sediments hardened into rock, meaning shells can now be found preserved in rocks from many different geological periods.
Amber
Amber is fossilised tree resin (tree sap). In some cases, insects and other small organisms became trapped in the sticky resin and were sealed inside as it hardened, resulting in exceptionally well-preserved fossils. Amber is highly sought after and is commonly used in jewellery.
Along the UK coast there are several locations where amber can be found, with Southwold being one of the most popular sites in East Anglia. Amber occurs in a range of colours, including orange, yellow, green, and red.
Coal, Gas, Oil
More commonly known as fossil fuels, these materials release carbon dioxide (CO₂) when burned. The increased levels of CO₂ in the atmosphere are believed to accelerate climate change by trapping heat and creating a greenhouse effect.
Coal is formed from the carbonised and compressed remains of ancient plants and some animals, which is why it is highly flammable. Oil also originates from the remains of ancient organisms, but it formed mainly in marine environments. Natural gas developed largely from decaying vegetation that was buried and altered over time.
Moulds and Casts
Fossils are often not the original remains of the plant or animal, but rather moulds or casts of them. During fossilisation, the original material can sometimes dissolve, leaving behind a hollow cavity in the surrounding rock. When this cavity later fills with minerals or other substances, it forms a fossil known as a mould.
Casts are another type of fossil. These are formed when a mould is later filled, creating a solid replica of the original organism. Examples of cast fossils include preserved footprints, animal trails, and other surface impressions.
Ripple Marks and Mud Cracks
Occasionally, rocks formed in shallow seas, lakes, or rivers preserve ancient ripple marks, created as soft mud was shaped by moving water and later dried. Mud cracks formed in a similar way, developing when wet, muddy surfaces dried out rapidly under warm conditions.
Both ripple marks and mud cracks provide valuable clues about the climate and environment at the time they formed. Their presence indicates that water was once present and that the area experienced warm, sunny conditions that allowed the mud to dry and harden.
Coprolites
Coprolites are the fossilised excrement of ancient animals. Over millions of years, the waste was buried by sediment and gradually hardened into stone through the process of fossilisation. Although they may appear unremarkable at first, coprolites provide valuable scientific information. By studying them, scientists can learn about the diet, behaviour, and even the health of prehistoric animals, as they often contain fragments of bone, plant material, or shells from the animal’s last meals.
Footprints (trace fossils)
Fossilised footprints of dinosaurs and ancient mammals can sometimes be found preserved in rock. The photograph shows a dinosaur footprint discovered at Hastings in the UK. These footprints formed under very specific conditions, when a dinosaur walked across soft, wet mud that was firm enough to hold its shape. Soon after, layers of sediment were deposited on top, protecting the impression from erosion. Over millions of years, these sediments hardened into rock, preserving the footprint as a fossil that can still be seen today.
Fossilised footprints provide important evidence of how ancient animals moved, their size, and even whether they travelled alone or in groups.
Borings (trace Fossils)
Borings are small channels and tunnels created by worms and molluscs that lived millions of years ago. These organisms burrowed into materials such as wood or shells while they were still soft or submerged in water. Over time, the surrounding material became fossilised, preserving the borings as evidence of ancient life. Fossilised borings can provide valuable information about past environments, including water conditions and the types of organisms that once lived there.
