Absolute dating A way of estimating the age of an object by measuring its chemical make-up. An example of absolute dating is radiocarbon dating.

Amber A hard yellow-orange substance formed when sticky tree resin is fossilized. Amber sometimes contains insects and other small animals that were trapped inside it.

Cast fossil A fossil formed when minerals fill in a mould fossil.

Coprolite Fossilized animal dung. Coprolites are a type of trace fossil. They can reveal what animals ate.

Excavation The process of examining layers of soil for fossils and other material from the past.

Fossil The remains of a once-living thing preserved in rock. Most living things are eaten or rot away when they die, leaving no trace. But sometimes, if animals are quickly buried by sediments, their remains may turn into rock and be preserved as fossils. After millions of years of Earth movements and the wearing away of rocks, some fossils may come to be exposed at the surface of the Earth. Fossils are the main way that we can learn about dinosaurs and other prehistoric life-forms.

Ichnite A fossilized footprint, a type of trace fossil. The depth of the prints and the distance between them can reveal how fast an animal walked or ran, and how heavy it was. Footprints also show whether an animal walked on two or four legs, and whether it lived alone or as part of a group.

Index fossil A common fossil that is known to date back to a particular time. Index fossils are used to date the layer of rock in which they are found. Ammonites and trilobites are excellent index fossils because they are abundant, easy to identify, and are known to come from a specific period in Earth’s history.

Matrix The rock in which fossils form.

Mineral A naturally occurring solid substance that is neither plant nor animal. Rocks are made up of minerals.

Mould fossil A hollow, bone-shaped hole, formed when the skeleton of an animal is dissolved by water underground.

Palaeontologist A scientist who studies fossils and other signs of life from the past.

Permineralization A fossil-forming process in which water seeps into the hollows in bones, plants or shells, and leaves hard mineral deposits in these spaces. The minerals make the remains harder, helping to preserve them in the ground.

Petrification A fossil-forming process in which water dissolves an organism’s remains, replacing them with minerals. These then harden into the shape of the organism itself.

Radiocarbon dating A way of calculating the age of an object by measuring how much carbon-14 (C-14) it contains. C-14 is a special form of the element carbon. It is radioactive, meaning that it regularly changes into different elements, a process called radioactive decay. All living things absorb C-14 from the atmosphere. When they die, they stop taking in carbon, and the C-14 within them starts to decay. Because it decays at a known rate, scientists can find out the age of an object by measuring how much C-14 is left. This method can be used to date objects back about 62,000 years. As most fossils are much older than this, other radioactive substances are used to date the rocks in which they are found.

Relative dating A way of estimating the age of an object by showing that it came before or after another object. Relative dating relies upon stratigraphy and index fossils. It is less exact than absolute dating.

Sediment Eroded rock fragments that are transported by wind, water or ice and laid down elsewhere. These fragments can cover skeletons and other once-living materials. This is the first stage in the formation of fossils.

Sedimentary rock A type of rock that is formed by the pressing together of rock fragments. These fragments, including sand, gravel and mud, are formed when other rock types are worn away by the wind and rain. They gradually settle in layers. As more layers settle on top of each other, the particles are compressed and cemented into sedimentary rock. Fossils are only found in sedimentary rocks.

Stratigraphy The study of rock layers, or strata. By estimating the order in which different rock layers were formed, scientists can guess the age of the fossils found within them. Deeper layers of rock are generally older than the layers above them.

Trace fossil The fossilized signs of the activity of life, such as footprints, droppings or animal burrows, giving important clues about how animals once lived, including those animals that are not themselves found as fossils.

Consultant: Ian Fairchild