Many of the layers also show a certain specialization.
Some layers contain mostly fish fossils while others contain land-dwelling creatures such as dinosaurs.
Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.
Since the geologic column represents millions of years of Earth's history, then obviously the fossils in each of the layers must be the same age as the layer in which they are found.Abandoned Wells: a hazard because wells left on vacated lands can channel water contaminated by pesticides and fertilizer straight down into the water table. Abrasion: the wearing away of rock surfaces by small particles moved by air or water.Abrasiveness also seems to be the one quality currently shared by most political appointees and prominent heads of state. Acid: a substance with a p H less than 7 due to prevalent hydrogen ions. The human stomach contains hydrochloric acid with a p H of 1; battery acid is stronger, but not by much. Acid Rain: precipitation heavy with nitric and sulfuric acid.Orpiment Orpiment has the formulae As2S3 and a relative hardness of 2.It is a rare mineral usually associated with realgar. Distinguished from sulphur by its perfect cleavage.