An explanation of the geologic time scale
The geologic time scale is the period of time covering the physical formation and development of Earth, especially the period prior to human history. The geologic time scale is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history.
How fossils and fossil records are used as evidence
The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change over the past four billion years. The picture may be smudged in places and may have bits missing, but fossil evidence clearly shows that life is old and has changed over time. That is how the fossils and fossil record are used as evidence.
Law of superposition
Archaeologists rely on the 'Law of Superposition' to help them identify and interpret stratigraphic layers. Stratigraphic layers are used in the study of sedimentary and layered volcanic rock. The Law of Superposition says that, under normal conditions, the layers get older the deeper you get.
How do scientists determine how eras start and end
The beginnings and ending of eras and periods was based on the observation that the fossil assemblage in the rocks changed in some fairly dramatic and distinct way: Often there were global extinctions related to climate change or other factors such as rapid radiations, which are reflected in the fossil assemblage. The boundaries were chosen to mark these changes. Only much later were ages in terms of millions of years added. This is why some eras are much longer than others, and the boundaries do not fall at any particular interval of time. So scientists determine which period rocks belong to by the fossil assemblage, on which the divisions were based in the first place.
The geologic time scale is the period of time covering the physical formation and development of Earth, especially the period prior to human history. The geologic time scale is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history.
How fossils and fossil records are used as evidence
The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change over the past four billion years. The picture may be smudged in places and may have bits missing, but fossil evidence clearly shows that life is old and has changed over time. That is how the fossils and fossil record are used as evidence.
Law of superposition
Archaeologists rely on the 'Law of Superposition' to help them identify and interpret stratigraphic layers. Stratigraphic layers are used in the study of sedimentary and layered volcanic rock. The Law of Superposition says that, under normal conditions, the layers get older the deeper you get.
How do scientists determine how eras start and end
The beginnings and ending of eras and periods was based on the observation that the fossil assemblage in the rocks changed in some fairly dramatic and distinct way: Often there were global extinctions related to climate change or other factors such as rapid radiations, which are reflected in the fossil assemblage. The boundaries were chosen to mark these changes. Only much later were ages in terms of millions of years added. This is why some eras are much longer than others, and the boundaries do not fall at any particular interval of time. So scientists determine which period rocks belong to by the fossil assemblage, on which the divisions were based in the first place.