Fossils are the preserved remains, or traces, of animals from our past. They can be hard parts such as mineralsised bones, shells and teeth, or they can be impressions or evidence of animals that once lived, for ecample currows, footprints, and even faeces.
The study of fossils is called palaeontology and is used in geology to learn more about our own evolution but also past environments on our planet. For example, from shells found at the top of the alps we know these rocks formed on the seafloor. Or from studying plant materials from millions of years ago we know that the proportion of gases int he atmosphere was different to today.
The olded fossils found on Earth are between 3.5 and 4billion years old - these were simple organisms that lived in shallow waters. Most fossils are used to (i) determine the environment of the rocks they are hosted in and (ii) calculate the ages of those rocks. There are two ways of calculating the age.
Absolute dating: this is where the actual age is measured using techniques such as radiometric or isotope dating.
Relative dating: this is estimating the age of a fossil/rock in relation to those above or below it in the stratigraphy - this is generally referred to as biostratigraphy.
Fossil range hugely in size (from the largest dinoasurs to microbes!) and composition. Most bones, teeth and shells will be comprosed of calcite or aragnonite, which has replaced the original calcium rich structure.
But not all tissues are replaced by minerals. In some cases such as insects in amber or mummies, the environment became sterile or dehydrated before decay of the animal.
Traces can be either the burrows or footprints or an animals or they can be the impression remaining after an animal has been resting in an area. In these cases, the animal either decayed without becoming mineralised, or moved on and did not die in situ.
If you are interested in Geological Survey Ireland's fossil collection, the full list can be found in our Catalogue
If you are interested in learning more about fossil, please viist our colleagues in the Museum of Ireland