Fourth Grade Earth Science
One way that earth science is beneficial to our current society is that it allows us to study the past as well as the creatures that lived in various points in time during earth's history. Being able to look back at what was left behind by other living organisms can tell us what happened to our earth and can prepare us for what to do in case it happens again. One such example is studying fossils. If the fossil of a certain animal found is extinct, scientists often determine what could have killed it off and if this factor is a threat towards us. The meteor that killed off many of the dinosaurs, for example, could be very threatening to humankind, though humans in some parts of the world can survive.
Another beneficial study in earth science is the study of systems or cycles that have been around for centuries. Like fossils, these cycles can tell us how our current earth came to be and why we have the kinds of flora (plant species) and fauna (animal species) that we presently see. A good example of a cycle that has been around for a very long time is the water cycle. This age‐old cycle is a combination of certain factors that are still present in our earth and still continue to work. It is a cycle that every living organism on earth depends on to survive and continue living, and it needs to be understood well in order to understand how our weather system works.
The Age of Fossils
You learned from previous science classes that when a living organism dies, and given the right conditions, it can leave behind a trace or imprint or something of itself. Thus, we say that a fossil is any living organism that has been preserved in some way in the materials in the earth's crust. There are several types of fossils. These are natural cast fossils, mold fossils, true form fossils, and trace fossils. The types of fossilization are replacement, carbonization or coalification, authigenic preservation, recrystalization, unaltered preservation, petrification, and freezing.
Many things can turn into fossils, but how can scientists tell how old a fossil is? To determine the age of a fossil, scientists use a method called carbon‐14 dating or radiometric dating. What they do is they measure the decay of certain elements found in the living organism's remains. For example, while alive, a dinosaur was absorbing carbon‐14 from the air. When it died, its body stopped absorbing carbon‐14, and instead, it started releasing it little by little in stages known as a half‐life.
A half‐life is the amount of time it takes for half of a certain substance to decay. Since scientists know the half‐life of certain substances or elements, (to put simply, they know the amount of time it will take for it to be reduced by half,) they can retrace the steps of the half‐life to determine how old the fossil is.
To illustrate, let's say you have a chocolate cake in front of you. Say it takes you half an hour to eat half of the cake, and you eat it. If a scientist comes across the cake and knows that it takes half an hour to eat half, then it knows that one hour ago the cake was still whole or “alive.” Half‐lives are estimates, though, as we will see in our science activity.
Another way to determine the age of fossils is to study the layers of rocks that you find them in. The earth's crust is made up of layers and these layers get added to overtime. After many years have passed, a layer that was originally on top can now be way down below. When a scientist finds a fossil in a certain layer of the earth's crust, and he knows when or at what time in history that layer was on top of all other layers, then he can give a date for when the fossil was likely to have been alive.
Determining the age of fossils tells us a lot about the history of our earth because we come to know what kinds of animals lived at different periods, as well as what their actions might have been. We benefit from studying all sorts fossils, but scientists especially love well preserved fossils. Some fossils are so well preserved that we are able to recreate the animal itself by piecing together its bone structure, much like the famous T‐Rex fossil in the Field Museum. This gives us an understanding of how tall, heavy, or menacing the animal was.
Next Article: Understanding Half Life
