Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages. The rocks formed during a period belong to a stratigraphic unit called a system.
Q. What is the past eon?
Eon, Long span of geologic time. In formal usage, eons are the longest portions of geologic time (eras are the second-longest). Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon.
Table of Contents
- Q. What is the past eon?
- Q. What is the recent era?
- Q. What is the longest part of Earth’s history?
- Q. What was probably the first organism on earth?
- Q. What are the 4 eons of Earth’s history in order?
- Q. What are the Earth’s eras in order?
- Q. What are the 7 epochs?
- Q. Which best describes eras and periods?
- Q. How many ages are there in history?
Q. What is the recent era?
Cenozoic Era
Q. What is the longest part of Earth’s history?
Earth Science Chapter 14 – History of the Earth
| A | B |
|---|---|
| Precambrian Time | Longest part of Earth’s history, starting at 4.0 billion years |
| Cyanobacteria | Photosynthetic bacteria thought to be one of Earth’s earliest life-forms |
| Paleozoic Era | When organisms developed hard parts and ended with mass extinctions |
Q. What was probably the first organism on earth?
Bacteria have been the very first organisms to live on Earth. They made their appearance 3 billion years ago in the waters of the first oceans. At first, there were only anaerobic heterotrophic bacteria (the primordial atmosphere was virtually oxygen-free).
Q. What are the 4 eons of Earth’s history in order?
Earth’s history is characterized by four eons; in order from oldest to youngest, these are the Hadeon, Archean, Proterozoic, and Phanerozoic.
Q. What are the Earth’s eras in order?
The Phanerozoic Eon is divided into three eras, the Paleozoic, Mesozoic and Cenozoic eras. These were named for the kinds of fossils that were present.
Q. What are the 7 epochs?
Divisions. The Cenozoic is divided into three periods: the Paleogene, Neogene, and Quaternary; and seven epochs: the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene.
Q. Which best describes eras and periods?
Eras have a smaller time span than periods. Eras and periods are independent of each other. Eras and periods both appear at the start of the Cambrian period. Eras were more recently established on the time scale than periods.
Q. How many ages are there in history?
five
