Leibnitz reworked Descartes's cosmogony. Protogea was published much later in
Acknowledgements Introduction his document discusses the way radiometric dating and stratigraphic principles are used to establish the conventional geological time scale.
It is not about the theory behind radiometric dating methods, it is about their application, and it therefore assumes the reader has some familiarity with the technique already refer to "Other Sources" for more information.
As an example of how they Sedimentary rocks essay used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale. To get to that point, there is also a historical discussion and description of non-radiometric dating methods.
A common form of criticism is to cite geologically complicated situations where the application of radiometric dating is very challenging.
These are often characterised as the norm, rather than the exception. I thought it would be useful to present an example where the geology is simple, and unsurprisingly, the method does work well, to show the quality of data that would have to be invalidated before a major revision of the geologic time scale could be accepted by conventional scientists.
Geochronologists do not claim that radiometric dating is foolproof no scientific method isbut it does work reliably for most samples.
It is these highly consistent and reliable samples, rather than the tricky ones, that have to be falsified for "young Earth" theories to have any scientific plausibility, not to mention the need to falsify huge amounts of evidence from other techniques.
This document is partly based on a prior posting composed in reply to Ted Holden. My thanks to both him and other critics for motivating me. Background Stratigraphic Principles and Relative Time Much of the Earth's geology consists of successional layers of different rock types, piled one on top of another.
The most common rocks observed in this form are sedimentary rocks derived from what were formerly sedimentsand extrusive igneous rocks e. The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy".
Fundamental to stratigraphy are a set of simple principles, based on elementary geometry, empirical observation of the way these rocks are deposited today, and gravity. A few principles were recognized and specified later.
An early summary of them is found in Charles Lyell's Principles of Geologypublished inand does not differ greatly from a modern formulation: The principle of superposition - in a vertical sequence of sedimentary or volcanic rocks, a higher rock unit is younger than a lower one.
The principle of original horizontality - rock layers were originally deposited close to horizontal. The principle of original lateral extension - A rock unit continues laterally unless there is a structure or change to prevent its extension.
The principle of cross-cutting relationships - a structure that cuts another is younger than the structure that is cut.
The principle of inclusion - a structure that is included in another is older than the including structure. The principle of "uniformitarianism" - processes operating in the past were constrained by the same "laws of physics" as operate today.
Note that these are principles. In no way are they meant to imply there are no exceptions. For example, the principle of superposition is based, fundamentally, on gravity. In order for a layer of material to be deposited, something has to be beneath it to support it.
It can't float in mid-air, particularly if the material involved is sand, mud, or molten rock.Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere.
The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. ABOUT THE AUTHORS Lorence G. Collins is a retired professor of geology from California State University, Northridge. He was educated at the University of Illinois and has special interests in the origin of granite and ore deposits.
Sedimentary Rocks - Sedimentary Rocks Sedimentary rocks are formed from layers of deposits laid down in lakes or seas. Over millions of years the layers of sediment build up resulting in the weight pressing downwards, creating high pressure, which squeezes the water out.
Figure 1. Sedimentary beds in outcrop, a graphical plot of a stratigraphic section, and a "way up" indicator example: wave ripples.
Minerals. For a material to be considered a mineral, the substance in question must meet the following criteria: Naturally occurring (not man-made).
Sedimentary rocks are the most common rock on earth. Sedimentary rocks form at, or very near, the Earth's surface where rocks particles transported by wind, water and ice are deposited on dry land, on the beds of rivers and lakes and in marine environments: beaches, deltas and the sea (Sedimentary Rocks, ).