Dating fossil framework man
Using fossils simply for identification purposes, Smith constructed a map of the various surface rocks outcropping throughout England, Wales, and southern Scotland.Smith’s geologic map was extremely crude, but in its effect on Earth study it was a milestone.In addition, its fossilized population should be sufficiently abundant for discovery to be highly probable.
The first step is determining whether similar beds in separated outcrops can actually be traced laterally until they are seen to be part of the same original layer.
Ideally, an index fossil should be such as to guarantee that its presence in two separated rocks indicates their synchroneity.
This requires that the lifespan of the fossil species be but a moment of time relative to the immensity of geologic history.
Such features as colour, ripple marks, mud cracks, raindrop imprints, and slump structures are directly observable in the field.
Properties derived from laboratory study include (1) size, shape, surface appearance, and degree of sorting of mineral grains, (2) specific mineral types present and their abundances, (3) elemental composition of the rock as a whole and of individual mineral components, (4) type and abundance of cementing agent, and (5) density, radioactivity, and electrical-magnetic-optical properties of the rock as a whole.
In other words, the fossil species must have had a short temporal range.