Nicolaus steno proposed the most basic principle of relative dating the law of
Duke Ferdinand appointed Steno to a hospital post that left him ample time for his research. Steno himself saw no difficulty in attributing the formation of most rocks to the flood mentioned in the Bible. Thus Steno's principle of original horizontality states that rock layers form in the horizontal position, and any deviations from this position are due to the rocks being disturbed later. The book's title is often simply abbreviated to Prodromus. Finally, in the case of strata, layers on top of a set of strata conform to the shape of lower layers.
However, he noticed that, of the two major rock types in the Apennine Mountains near Florence, the lower layers had no fossils, while the upper ones were rich in fossils. He never wrote the larger work for which his Prodromus was meant to serve only as an introduction. Steno was able to show by this reasoning that fossils and crystals must have solidified before the host rock that contains them was formed. The Hadean, the Archean, and the Proterozoic eons are commonly referred to as the Precambrian.
These, Steno argued, must have grown from fluids percolating within the Earth, in the same manner that crystals could be made to grow in chemistry experiments. Assuming that all rocks and minerals had once been fluid, Steno reasoned that rock strata and similar deposits were formed when particles in a fluid such as water fell to the bottom. Molten rock may force its way through surrounding rocks and may sometimes squeeze between older rock layers, also forming an exception to Steno's law. Steno's work on shark teeth led him to the more general question of how any solid object could come to be found inside another solid object, pay per click search search engine shopping email dating such as a rock or a layer of rock.
This process would leave horizontal layers. Others were of the opinion, also going back to ancient times, that fossils naturally grew in the rocks. Ancient authorities, such as the Roman author Pliny the Elder, had suggested that these stones fell from the sky or from the moon. Steno's contemporaries Robert Hooke and John Ray also argued that fossils were the remains of once-living organisms.
All rocks can be dated radiometrically. He recognized that rocks might be uplifted by subterranean forces.
He suggested that the upper layers had formed in the Flood, after the creation of life, while the lower ones had formed before life had existed. During radioactive decay, as the percentage of radioactive parent atoms declines, the proportion of stable daughter atoms also decreases.