The Geologic time scale
What is the Geologic Time Scale?
“Geologic time is the 4.6 Billion year history of Earth, from its origin to the present, as inferred from the rock record, both on Earth and the Moon.
Geologic time is divided into a four-level of time intervals:
EONS -- The first and largest division of geologic time.
ERAS -- The second division of geologic time; each era has at least two periods.
PERIODS-- The third division of geologic time. Periods are named for either location or characteristics of the defining rock formations.
Location = the region where the period's characteristic rocks were first studied.
Characteristics = the nature of the unique system of rocks and rock formations that define the Period.
EPOCHS -- The fourth division of geologic time; represents the subdivisions of a period
The first geologic time scale was proposed in 1913 by the British geologist Arthur Holmes (1890 - 1965). This was soon after the discovery of radioactivity, and using it, Holmes estimated that the Earth was about 4 billion years old - this was much greater than previously believed.
A fossil is the naturally preserved remains or traces of animals or plants that lived in the geologic past. There are two main types of fossils, body, and trace. Body fossils include the remains of organisms that were once living(plants, animals, others) and trace fossils are the signs that organisms were present (footprints, tracks, trails, and burrows). Determining the age of a rock involves using minerals that contain naturally-occurring radioactive elements and measuring the amount of change decay in those elements to calculate approximately how many years ago the rock formed.
What is the Geologic Time Scale?
“Geologic time is the 4.6 Billion year history of Earth, from its origin to the present, as inferred from the rock record, both on Earth and the Moon.
Geologic time is divided into a four-level of time intervals:
EONS -- The first and largest division of geologic time.
ERAS -- The second division of geologic time; each era has at least two periods.
PERIODS-- The third division of geologic time. Periods are named for either location or characteristics of the defining rock formations.
Location = the region where the period's characteristic rocks were first studied.
Characteristics = the nature of the unique system of rocks and rock formations that define the Period.
EPOCHS -- The fourth division of geologic time; represents the subdivisions of a period
The first geologic time scale was proposed in 1913 by the British geologist Arthur Holmes (1890 - 1965). This was soon after the discovery of radioactivity, and using it, Holmes estimated that the Earth was about 4 billion years old - this was much greater than previously believed.
- The law of superposition helps us understand relative age relationships of fossils found in sedimentary rock layers.
- The oldest rocks are at the bottom, and the youngest at the top, illustrating the law of superposition.
A fossil is the naturally preserved remains or traces of animals or plants that lived in the geologic past. There are two main types of fossils, body, and trace. Body fossils include the remains of organisms that were once living(plants, animals, others) and trace fossils are the signs that organisms were present (footprints, tracks, trails, and burrows). Determining the age of a rock involves using minerals that contain naturally-occurring radioactive elements and measuring the amount of change decay in those elements to calculate approximately how many years ago the rock formed.