First appearance datum
Encyclopedia
First appearance datum is a term used by geologist
s and paleontologists
to designate the first (oldest) appearance of a species in the geologic record. In other words, FADs represent the geologically oldest fossil of a particular species that has yet been discovered.
FADs are frequently used to designate segments in the Geologic time scale
. For example, the beginning of the Tremadocian Stage of the Ordovician
Period is marked by the first appearance (FAD) of the conodont
Iapetognathus fluctivagus in the geologic record. This occurs in bed
23 of the rock formation known as the Green Point section, located in western Newfoundland, as well as in geologically correlated strata
in many parts of the world.
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
s and paleontologists
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
to designate the first (oldest) appearance of a species in the geologic record. In other words, FADs represent the geologically oldest fossil of a particular species that has yet been discovered.
FADs are frequently used to designate segments in the Geologic time scale
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
. For example, the beginning of the Tremadocian Stage of the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
Period is marked by the first appearance (FAD) of the conodont
Conodont
Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...
Iapetognathus fluctivagus in the geologic record. This occurs in bed
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
23 of the rock formation known as the Green Point section, located in western Newfoundland, as well as in geologically correlated strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
in many parts of the world.