First appearance datum is a term used by geologists 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.
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Famous quotes containing the words appearance and/or datum:
“Do not look on his appearance or on the height of his stature, because I have rejected him; for the LORD does not see as mortals see; they look on the outward appearance, but the LORD looks on the heart.”
—Bible: Hebrew, 1 Samuel 16:7.
“Language fails not because thought fails, but because no verbal symbols can do justice to the fullness and richness of thought. If we are to continue talking about “data” in any other sense than as reflective distinctions, the original datum is always such a qualitative whole.”
—John Dewey (1859–1952)