What is Paleontology?

Meaning of Paleontology

The earth has been here for approximately 4.6 billion years and has a long legacy of a diverse collection of species and events that ultimately led to the era that we as humans live in now. Even though humans have lived only for a small fraction of the 4.6 billion years, we can glean information about what it was like in the past by analyzing and studying fossils, rock formations, and other signs in nature. Paleontology offers itself as a tool and scope through which you can view the world; it reminds you that humans are just one of the many million species that have roamed on this Earth. Paleontology is a branch of science that aims to paint a picture of the past, a place that we no longer have direct access to. However, paleontology acts as the bridge that connects us and gives us the ability to travel through time.

Bridge, Black And White, Black, White, Architecture

The Beginnings

Earth at the beginning was an inferno, being hit by asteroids, and having volcanoes that expelled gases, like carbon dioxide, ammonia, and methane into an atmosphere. Even the oceans were filled with dangerous chemicals. It was a toxic wasteland, extremely unsuitable for life and vastly different from the beautiful Earth that we know today. Fast forward a bit and the earth starts to form its crust after some of the heat dissipates. This crust wasn’t a smooth and continuous eggshell that wrapped around all of earth. Instead, it was a cracked egg shell due to the motion of hot magma below. When you boil water, the water is heated from the bottom and that water then rises. When it reaches the surface it spreads outwards to the sides and then cools before sinking back down to be reheated. This is the convection current as shown in the figure below. Similarly, the core of the Earth heated the molten rock and led to the convection current, ultimately leading to the cracks in the crust. These cracks then formed what we call tectonic plates that are constantly in motion and changing thanks to convection currents. The basaltic rocks of the oceanic crust is often heavier which leads to continental crust “floating” above. The continental tectonic plates move along due to tectonic plates like something on a conveyor belt. As you could guess, this can lead to plates colliding, which has lead to some of the most beautiful landmarks, mountain chains all over the world. The Himalayas, the Rockies, and the Alps are all examples of mountain chains that were created through tectonic plates and convection current.

So why should a paleontologist care about any of this? Fossils and signs from history are stored in the rocks of the Earth so its imperative to understand how the Earth came about and understand that the world is dynamic and fluid. The world has undergone change constantly, for there wasn’t always seven continents. 180 million years ago there was a supercontinent called Pangea which eventually split into two continents called Laurasia and Gondwana. Finally these continents split into what we know as the seven continents today. Below you can see a graphic that shows the splitting of Pangea into the Earth that we know today.

ConvectionPangea_animation_03

https://upload.wikimedia.org/wikipedia/commons/0/08/Convection.gif

Rocks

There are three types of rocks: metamorphic, igneous, and sedimentary. Metamorphic rocks are formed through high pressure nad heat, igneous rocks are made from the cooling of magma, and sedimentary rocks are made from particles of other rocks which were transported and compacted by wind and water. Fossils are mostly found in sedimentary rocks because fossilization is a truly delicate process. Usually only the hard parts of an organism make it through, but sometimes soft part can leave impressions into sediment. Even the hard parts have a difficult time of being fossilized, for the remains could be eliminated by scavengers, bacteria, water, and wind can all contribute to the fossils’ demise. Paleontologists usually only find fragments at a time. It is rarely them finding a whole complete skeleton lying there waiting to be discovered.

Relative Dating and Geological Time Scale

So what can we learn from rocks? Paleontologists and geologists can glean some information from the rock structures that contain fossils. Sedimentary rocks usually stack themselves in layers called strata. First, the law of superposition states that the oldest strata lies at the bottom and that newer strata is near the top layers. Paleontologists also understood that fossils called index fossils were widely dispersed organisms that were known to be alive in certain periods of time. These fossils acted as references so that paleontologists could sort out the how old everything was relative to each other. Paleontologists attempting to date and segment periods of time led to the rise of the geological time scale.

File:Geological time spiral.png

By United States Geological Survey [Public domain], via Wikimedia Commons

Chronometric Dating

Nowadays, dating relies on the radioactivity of chemical isotopes. Certain isotopes decay to a stable state at a constant rate unaffected by environmental factors. Hence, if we measure how much has decayed, we can determine the age of the compound that we are dealing with. This rate of decay is in terms of the isotope’s half-life, the time it takes for half of the isotope to decay. Potassium/Argon and Argon/argon techniques are used to date very old rocks currently. However, this provides us  with the age of the rock and not a fossil specimen. To date fossils, paleontologists use radiocarbon dating is used with the C14 isotope which is incorporated in all living things thanks to the carbon cycle as seen below. The C14 isotope only has a half-life of 5,730 years which is relatively short so it can only be used for samples up to 40,000 years old. Potassium/Argon dating can date rocks much older than that.

File:Carbon cycle-cute diagram.svg

By Carbon_cycle-cute_diagram.jpeg: User Kevin Saff on en.wikipedia Derivative work: FischX [Public domain], via Wikimedia Commons

What Can Fossils Tell Us Then?

The first step for a paleontologist is to classify the specimen and decide what family it belongs to, or whether its a new species that needs to be created for it. Taxonomy, the system with which the fossils are named, is crucial because giving fossils names allow us to understand what its relatives are and communicate with other paleontologists about what we are referring to. Next, the most obvious characteristic of the fossil specimen that you are studying is its morphology, its appearance. Looking at its structure, paleontologists can infer about some of the limitations and hypothesize about what certain structures could be used for. For instance, the velociraptor’s talon was thought to be used to disembowel and tear the flesh of its prey, but new research on the strength of the talon has led to us to believe that the velociraptor used its talons to pin down its prey. Another example, is the teeth of dinosaurs. The teeth of a stegosaurus  provides evidence of its dietary habits as a herbivore. Many different theories emerge then to explain what paleontologists see which can be problematic because usually observations are based on only a few fossils that are found. Hence, using a small sample size, paleontologists often have to extrapolate and generalize a population through the characteristics seen in the small group of fossils available to them. Fossils are like clues of a larger puzzle of the past that paleontologists must struggle to piece together in order to see how fast a T-Rex would run or whether triceratops used its horns in combat. Paleontology offers itself as a lens for people to look into the past to travel in time to better understand what life was like before us and about how these past conditions culminated to our present situation. It really does make you appreciate Earth a lot more and make you think of how little time humans have lived on Earth.

Meaning of Paleontology

Works Cited
Tattersall, Ian. Paleontology: A Brief History of Life. West Conshohocken, PA: Templeton, 2010. Print.