Overview: Since its formation 4.6 billion years ago, the Earth has been changing constantly. For the past 3.5 billion years or so, life has also been changing constantly.
Most of these changes are gradual, or slow and steady. For example, weathering and erosion shape the landscape around us, wearing down mountains, moving sediments around, and carving out canyons and caves. Similarly, living things develop new features through small changes over many, many generations.
Earth's history has also included big changes that happened more quickly, and scientists use these major events as dividing points between different eras, or chapters in geologic time. Often a major geological change, like increased volcanic activity led to a major biological change, like a mass extinction. Sometimes it worked the other way around, like when the evolution of plant-like bacteria changed the composition of the atmosphere by adding lots of oxygen.
Scientists are able to understand things that happened millions and even billions of years ago by looking for clues left behind in the rocks that formed back then. The deeper we dig into rock layers, the farther back in time we can see. Fossils show us what kinds of living things were around during different time periods. When we put together the fossils and other clues from rocks all over the world, it's like a geological history book: each layer of rock is like a page in the history of the planet.
GEOLOGY: The study of Earth's physical structures (including rocks and minerals) and the processes that change them over time
BIOLOGY: The study of living things
Earth's History: A Trip Through Geologic Time
Looking for information to help you with your History of the Earth storybook?
Start with this 3-minute video about how Earth formed, how we got oceans, and how life has changed over time: History Channel: Planet Earth
Then check out this site, which has a ton of information: BBC nature: History of Life on Earth
Two visual ways to represent the timeline of life's evolution through the geologic eras.
These two videos take us on a trip through time to revisit the 5 major mass extinction events that have impacted species over the Earth's history, and leave us with some thoughts about what seems to be a sixth mass extinction in the making...and this time, we're the asteroid.
Peering into the Past: The Fossil Record
Processes of Change: Continental Drift
Processes of Change: Weathering and Erosion
Examples of chemical weathering: