After reading the CK-12 Chapter 12 sections 12:3, 12:5, 12:7, 12:11, and 12:13, I acquired a vast amount of new knowledge about Earth’s history. I had a little background knowledge on fossilization, but the articles made me realize that the best fossils are the ones you can extract DNA from, a kind of “blueprint” for life. It encodes everything, from traits to appearance, in the form of proteins, extremely beneficial to scientists for learning more about the planet’s past. Also, there were two types of fossilization, trace fossils and body fossils. Trace fossils are not fossils of an organism itself, but of the traces it left, like footprints or nests or eggs. Body fossils depict the actual body of an organism. Fossils are also the best clues to life on Earth before humans and dinosaurs, and index fossils helps determine the age of rocks.
Speaking of the age of rocks, the chapter also led me to contact an area I had not heard of before: relative dating. In early geology, geologists had no method of determining the exact age of geologic material. Thus, a principle called Stero’s principle allowed the relative ages of the rocks to be found, stating that older rock layers lie underneath newer ones. If we know the relative ages of 2 rock layers, we know if one is older and one is younger, but we do not know how old they are in years.
The age of rocks is also interrelated with the geologic time scale, which divides the whopping 4.6 billion year history of the Earth into smaller sections. From largest to smallest: Eons, eras, Periods, and Enochs. Divisions in Earth’s history are all recorded on this scale, and they usually signalled major events in life. For example, the end of the Cretaceous period marked the extinction of the dinosaurs. European geologists were the first to put together the geologic time scale. The Jurrasic period was named after the Jura mountains in France and Switzerland, to prove that point.
The act of putting together events in order requires the correlation of rock layers, or the relative age of rocks as mentioned previously. Early geologic time scales only depicted the order of the events, but the discovery of radioactivity allowed scientists to conduct radiometric dating and carbon dating to produce the age of rocks in years. Thus, dates were assigned to time scale divisions.
The geoligic time scale starts at the formation of the Earth, which was formed 4,600 million (or 4.6 billion) years ago and shares the same age as the rest of the solar system. The age was figured out by radiometric dating. The formation of the Earth occurred when materials at similar distances orbiting the new star, the sun, collided with each other. The collisions resulted in a large mass that increased drastically in temperature due to the increasing number of collisions, and rock and metal melted into layers. Gravity caused the denser materials to get pulled to the center, while the lighter ones rose up to the surface. This explains the composition of the inside of the Earth today: The inner and outer core is made of metal and iron, dense materials, while the mantle is made of rock and the crust is made of light materials like soil, aluminum, and other minerals low in density.
The formation of the moon is different than the formation of the Earth. During the early stages in the solar system, space debris was abundant, and an asteroid the size of Mars collided with the Earth. The impact melted most of the Earth along with the entire asteroid and the materials were sent into orbit. Over time, the materials collided with each other and formed the moon, which occured 70 million years after the Earth was formed.
This was all the new information that I gathered from reading CK-12 Chapter 12.