Module 9: Earth’s History

Earth’s history is not easily pieced together. You might think that getting an accurate and detailed history of Earth is an easy task. However, this is not the case. Earth is 4.6 billion years old. The earliest human fossils found date back to an estimated 195,000 years ago. When compared to the age of Earth, humans have only lived on the planet for a small fraction of time. Dinosaurs have a longer evolutionary record than humans. Dinosaurs roamed the planet for an estimated 65 million years.

It may help to think about the history of Earth like a large, old textbook. The oldest pages are found near the back of the book, with the youngest pages found towards the front cover. The textbook is tattered, missing pages, and even missing entire chapters. The rock record of Earth should give scientists a full picture of history. But, like the textbook, the rock record has been altered and in some areas destroyed. There is still enough of the rock record to piece together the history of Earth, but it will take investigations of both the rocks and fossils to re-create the story. In this module, you will explore the different ways scientists learn about the history of Earth. You will begin by studying the clues that are found in the rock record. You will learn how the age of rocks and fossils can be determined scientifically through different dating techniques. You will explore the formation of the many types of fossils to understand how scientists decoded Earth’s history, allowing for the construction of a geologic time scale.

Getting Started

A type of geologist, called a paleontologist, is responsible for the investigation of fossils. Paleontologists begin by extracting a fossil from sedimentary rock. It is possible that the fossil was persevered in the rock for over a billion years. The paleontologist acts like a crime scene investigator. They try to piece together the life and death of the organism. Often, paleontologists will not get the luxury of extracting the bones and hard parts from the entire organism. Sometimes, they have to piece together the life of the organism with only a few fragments.

From studying fossils, paleontologists are able to describe the history of the Earth. The organisms that lived on the planet can help draw a picture of what life was like during different periods in Earth’s long history. View the video, Fossils | Science Trek, from eMediaVA℠ to investigate the ways that fossils are formed and how paleontologists piece together the fossil record.

 

Key Vocabulary

To view the definitions for these key vocabulary terms, visit the course glossary.

actual remains	half-life	radioactive decay
cast	isotope	radiometric dating
daughter isotope	Law of Original Horizontality	relative age dating
eon	mass extinction	rock correlation
epoch	mold	rock record
era	paleontologist	trace fossil
extinct	parent isotope	unconformity
fossil	period	uniformitarianism
fossil record	Principle of Superposition
geologic time scale	Principle of Cross-Cutting Relations