Fossils are cool. Thanks to a huge amount of cultural exposure and the six Jurassic Park and Jurassic World movies, everyone loves dinosaurs (fig. 1.1). Lots of people enjoy collecting fossils for fun as well, whether they are fossil shells or amazing extinct creatures such as trilobites. Today you can buy all sorts of amazing fossils online and in rock shops around the world.
Figure 1.1 ▲
Skeleton of “Black Beauty,” a complete, articulated Tyrannosaurus rex specimen from Montana, now in the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta. Paleontologist Ashley Fragomeni Hall for scale. (Courtesy of A. Hall)
Fossils are cool by themselves, but they also provide a window into the prehistoric past. We can now visualize immense dinosaurs, larger than any land animal alive today; fantastic sea creatures such as the terrifying sea reptiles known as ichthyosaurs, mosasaurs, and plesiosaurs; and sea floors populated by gigantic shelled squids, huge “sea scorpions,” and incredible predatory fish.
But it’s not just these extinct creatures that are important. Fossils are the best clues we have to understanding the environments of the ancient past. They tell us whether a pile of rocks represents an ancient floodplain, an ancient sea bottom, or a long-gone swamp or lagoon. We can now reconstruct ancient environments at a level unimaginable just a few decades ago. This, in turn, lets us look at issues like past climate changes: episodes of warming, when greenhouse gases warmed the planet and oceans drowned the continents, and times when the world was frozen from the poles almost to the equator. We can reconstruct ancient ocean currents and ancient weather patterns as well. Finally, fossils are the primary means used by geologists to date rocks. Without fossils we could not tell geologic time.
Fossils are really important for our civilization for other reasons too. Not only do they tell us about ancient climates, but fossils (and the life they represent) controlled our climate in the geologic past. Ancient bacteria were responsible for giving our planet the oxygen we breathe—and algae in the oceans remain the major providers of oxygen. Without these organisms, this planet would have been as lifeless as Mars or any other body in space. The next time you see some pond scum, thank them for your ability to breathe!
Thick deposits of coal (fig. 1.2A) are the remnants of huge swamps that did not decay; as the trees fell, their material was locked up in the earth’s crust and became the black rock we burn today. Ancient limestones (fig. 1.2B) are remnants of tropical lagoons similar to those in the Bahamas or the South Pacific today. Their trillions of shells also locked up a huge amount of carbon in the earth’s crust as calcium carbonate, or calcite. Together, coal and limestone are the great regulators of carbon dioxide in our atmosphere. When they lock up lots of carbon in the crust, the planet can go into an icehouse state. When we burn lots of coal (as we do today), the trapped greenhouse gases are released into the atmosphere and global warming occurs.
Figure 1.2 ▲
Many extinct organisms are responsible for controlling our climate: (A) A coal seam, which is made of the remnants of thousands of plants that turned to stone instead of decaying. (B) A fossiliferous limestone from the Late Silurian Wenlock Limestone, Dudley, UK. The large triangular object (right center) is the tail segment of the trilobite Dalmanites. The honeycombed objects are pieces of the coral Favosites. The long cone (left center) is a straight-shelled orthocone nautiloid. There are numerous brachiopods such as Atrypa, Leptaena, and rhynchonellids, as well as branching bryozoans such as Favositella, and stems of crinoids. ([A] Photograph by the author; [B] courtesy of Wikimedia Commons)
Contrary to the popular myth, all the oil and gas that we use did not come from decayed dinosaurs. Instead, it is from the shells of trillions of plankton that once lived on the surface of the ocean and are now buried in deep-sea muds. Just like burning coal, when we burn these fossil fuels, we release the trapped carbon dioxide that was entombed in the crust, which contributes to climate change.
So fossils are not just cool; they tell us amazing stories about the past. The life that fossils represent helps us know why our climate has changed and the vital role oxygen has played in life on this earth. As we burn those same fossils, which are now extracted as oil and coal, we are changing our climate yet again. And we may be transforming the earth in ways that might not be good for our future.
