Earth Science: Biology – Evolution – Geological Eras
In the 18th century people still thought that the Earth was relatively young. This had become common belief after an Irish bishop interpreted the Bible and concluded that the world was created on October 26, 4004 B.C.
However, scientists’ claim that the creation and decay of rock material was an extremely lengthy process were increasingly convincing. Within this geological time frame, the chronology of the Earth could be determined more accurately, all the way back to its formation 4.56 billion years ago.
Earth Science: Biology – Evolution -Stratigraphy
Stratigraphy is one of the oldest and most important geological dating methods. A time scale of past geological events can be produced from the sequence of rock deposits.
A Danish naturalist, Nicolaus Steno (1638-1686), was one of the first scientists to define the fundamental laws of stratigraphy. He discovered that lower rock layers are older than the layers above, as long as they remain undisturbed. Movements of the Earth, however, do happen and the stratigraphic sequence may be ambiguous and sometimes incomplete due to erosion, folding mountain ranges or other geological movements of the rock.
Such ambiguities and gaps in the rock layers may not affect Steno’s law of superposition but can frequently alter the layering sequence. So-called marker beds formed by events such as the ash rain from an active volcano can also help in dating rock strata or layers.
Describing the thickness and sequence of rock layers (lithostratigraphy) is not sufficient to determine the age or duration of its creation. This information is derived from fossils and other objects embedded in the rock strata (bio- stratigraphy). Only certain fossils are suitable for age determination. These index fossils are the remains or traces of plant and animal species that existed for only a short time (geologically speaking, which can be up to a few million years) and that were geographically wide spread and abundant
These factors are important so that even rock layers at a distance from each other can be compared by identifiable, easily found fossils. Relative age determination allows geologists to divide the Earth’s history into different time intervals, called eras, periods, and epochs, to be used as a frame of reference for what order the formation of the Earth’s surface and the origin and evolution of plant and animal species occurred in.
The absolute age de- termination (a numerical measurement of time passed) of rocks and fossils was only possible with the discovery of radioactive decay by French physicist Antoine Henri Becquerel (1852-1908) for which he recieved the Nobel Prize in physics. The subsequent development of radio-dating methods also allowed a more precise age determination of geological periods.
ORGINATOR OF BIOLOGICAL STRATIGRAPHY
The British surveyor William Smith realized during canal works that rock layers of matching ages also contained the same types of fossils. He created a geological map of Great Britain based on the fossils he found; it was published in 1815.
Initially, his work was scoffed at by renowned geographers but in 1831, the scientific community finally recognized his achievements and Smith was the first to be awarded the Wollaston Medal by the Geological Society for outstanding accomplishments in geology.