Facts for Fossils & Imprints

Fossils are, without the shadow of a doubt, one of the most important tools used by scientists to peer back into times long gone. Without them, the biological past would be lost to dust of history. Luckily, though, fossils are not only useful, but abundant, and they exist in the utmost variety, each with their own story to tell.

  1. What is a Fossil?

    • In short, fossils are the preserved evidence of a long-dead organism, whether it be teeth, bones, footprints or eggs. They can be a found all over the world, from mountaintops to deep trenches. With a trained eye, scientists can examine fossils and make determinations about the past. Though there are many types of fossils, the two you might most commonly come across are imprints, which can be either types of trace fossils or molds, or the skeletons like the ones seen in museums, which are created via another process entirely.

    Imprints

    • The definition of imprint fossils is in the word, but they come in several different forms. A rock with fossilized shape pressed into it representing evidence of an organism is, essentially, an imprint fossil. A good example would be dinosaur tracks, which get preserved over time. However, there are other types of imprint fossils that are much more common.

    Molds

    • A mold is an imprint of an organism in the rock and is created through a fairly simple process. First, an organism, usually one with a hardened exterior like that of a bivalve, dies and is covered up by sediment. Over time, the sediment hardens, while simultaneously the deceased organism dissolves. Over the eons, when the sediment has completely solidified and is found by a scientist, what remains will be rock with the imprint, or an internal mold, of the bivalve. These are extremely common and can be found at virtually any museum in the world. They give us a detailed look at extinct organisms, but there's a rarer occurrence that involves molds that gives us a more complete picture.

    Casts

    • Casts are rarer and are essentially a stone model of an extinct organism. They're created in a similar fashion to internal molds, with one exception. After the organism dissolves, the resulting mold is filled with another type of sediment. Later, when the scientist finds the rock, what they'll discover won't be an imprint, but a complete rocky clone of the organism that perished.

    Permineralization

    • The most recognizable fossils in the world, permineralized remains can typically be found standing proudly in the dinosaur halls of museums everywhere as the skeletons of dinosaurs like tyrannosaurus rex or triceratops. These fossils, which are coveted and enjoyed by millions, are created through a unique process called permineralization. When an organism like a dinosaur died, it was covered by sediment. Over the ages, mineral-laced groundwater seeps into the empty, porous spaces in the bones and they literally mineralize, turning the bone into rock. Mineralization is responsible for some of the most detailed fossils ever found, and offers the clearest glimpse into the prehistoric past.