How long is an era in geology?
A geological era is a large period of time that is broken down into smaller time frames called periods, and is generally marked by some type of extinction event.
The beginning of the Paleozoic era (543 million years ago) is marked by an explosion of life such as trilobites and other animals as discovered in the Burgess Shale. The end of the Paleozoic era/beginning of the Mesozoic era (248 million years ago) is marked by an extinction event called the Permo-Triassic extinction event. The end of the last period of the Paleozoic era, called the Permian, saw the largest extinction event known in paleontology. 97% of all marine life was killed and 70% of all families on land went extinct. The first period in the Mesozoic era is the Triassic, hence the name ‘Permo-Triassic’ extinction.
The end of the Mesozoic era/beginning of the Cenozoic era (65 million years ago) is marked by what is referred to as the K-T extinction. At that time a meteor hit in the Yucatan peninsula creating the Chixulub crater. The impact was large enough that more than three-fourths of all life on Earth went extinct, including the last of the few remaining dinosaurs.
We are currently in the Cenozoic, and so no end has yet been determined.
Our word era was borrowed from a Latin word for the brass counters used to keep accounts. Accounts suggest bookkeeping, which suggests a period of time. An era came to mean a period of time starting on a certain date, and in modern language its length may be brief or immensely long. There is plenty of reason for us to become confused about this small word. Since Roman days, when it was a brass money counter, it has taken on many meanings. As a rule it is a period of time, but the duration of time may vary. The Christian era is some 2000 years old. The era of a king may be a generation. The era of the auto began in the days of your grandparents, and sometimes era and day or days have the same meaning. The eras of geological history are immense periods of time covering hundreds of millions of years. But they are eras nonetheless and as eras are related indirectly to the word day. They could be those stupendous days of the Earth’s creation, for each covers a stage in the miraculous develo
