The geologic timescale. The column on the right is the enlarged top section of the column on the left.
Modified from USGS
Geologic Time: Our Earth Is Old!
We know that the Earth is very old. Scientists currently understand that it is about 4.6 billion years old. (That's 4,600,000,000 years!) This huge amount of time is called geologic time. The evidence of Earth’s age comes from its rocks. The rocks that are exposed at Earth’s surface are all different ages. Some are quite young, made in the past few million years. Others are quite old – many millions or even billions of years old. These old rocks are usually quite deep within the Earth’s crust but are often exposed as plate tectonics pushes ancient rocks to the surface. Scientists who study rock layers developed a timeline of Earth history called the geologic time scale to describe the ages of various rock layers.
The geologic time scale expresses the 4.6 billion years of geologic time along a timeline that is divided into sections. Broad sections of time are called Eras and smaller sections of time are called Periods. Having names for the different sections of time helps people communicate about when events happened long ago such as when a dinosaur lived, when a volcano erupted, or when an asteroid hit.
Shop Windows to the Universe Science Store!
The Fall 2010 issue of The Earth Scientist
, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!
You might also be interested in:
Scientists have known for a long time that whales, the largest marine mammals, have distant relatives that lived on land millions of years ago. Little was known about whales’ land-loving ancestors until...more
To predict the future diversity of life on Earth, scientists are turning to the fossil record of marine creatures – the ancestors of snails, clams, sand dollars, and crabs. Diversity is the number of species...more
If you went looking for frogs today on the island of Madagascar, the largest one you could find would be just over four inches long. But if you went looking for frogs more than 65 million years ago, you...more
Tens of millions of years before dinosaurs roamed Earth, their ancestors were all but eliminated in a catastrophic event called the Permian Mass Extinction. This was the greatest extinction event ever...more
Measuring sea level, the height of the ocean surface, allows scientists to calculate whether sea level is changing over time and how much sea level rise is happening now because of global warming. But...more
About 250 million years ago, almost all of the life in the sea became extinct – about 95% of species. This was during a huge mass extinction. Mass extinctions happen when the number of species decreases...more
Earth is old, 4.6 billion years old to be exact. But there isn’t much hanging around the planet from those early days. That’s because our planet is a great recycler. Most of the rocks that were formed...more