Its History and Development Scottish geologist James Hutton set the stage for the development of the geologic time scale in the late 18th century with the publication of his Theory of the Earth In it, Hutton advanced “uniformitarianism,” a geological doctrine which basically assumes that current geologic processes, occurring at the same rates observed today, in the same manner, account for all of Earth’s geological features, a principle later championed by British geologist Sir Charles Lyell Next, British civil engineer, surveyor and amateur geologist William Smith made the discovery that fossils are found buried in a definite order. The geologic time scale was developed shortly thereafter. What is the geologic time scale and how does it work? Well, the earth’s crust consists of many layers of sedimentary rock called “strata”. Geologists assume that each layer represents a long period of time, typically millions of years. This is actually a secondary assumption based upon the primary assumption of Uniformitarianism.
Radiometric Dating and the Geological Time Scale
See Article History Geologic history of Earth, evolution of the continents , oceans , atmosphere , and biosphere. By studying this rock record from the very beginning, it is thus possible to trace their development and the resultant changes through time. The pregeologic period From the point at which the planet first began to form, the history of Earth spans approximately 4. The oldest known rocks—the faux amphibolites of the Nuvvuagittuq greenstone belt in Quebec , Canada—however, have an isotopic age of 4.
There is in effect a stretch of approximately million years for which no geologic record for rocks exists, and the evolution of this pregeologic period of time is, not surprisingly, the subject of much speculation. To understand this little-known period, the following factors have to be considered:
Geologists have done the same thing to geologic time by dividing the Earth’s history into Eras — broad spans based on the general character of life that existed during these times — and Periods — shorter spans based partly on evidence of major disturbances of the Earth’s crust.
One of the very foundations of evolution and popular science today is the “geologic column. Although not found in all locations and although it varies in thickness as well as the numbers of layers present, this column can be found generally over the entire globe. Many of its layers can even be found on top of great mountains – such as Mt. Everest and the American Rockies.
In some places, such as the mile deep Grand Canyon, the layers of the column have been revealed in dramatic display. Certainly the existence of the column and its layered nature is quite clear, but what does it mean? Is it really a record of millions and even billions of years of Earth’s history? Or, viewed from a different perspective perhaps, does it say something else entirely? As one looks at the geologic column, it is obvious that the contact zones, between the various layers, are generally very flat and smooth relative to each other though the layers may be tilted relative to what is currently horizontal or even warped since their original “flat” formation.
Many of the layers extend over hundreds of thousands of square miles and yet their contact zones remain as smooth and parallel with each other as if sheets of glass were laid on top of one another before they were warped.
How Good Are Those Young-Earth Arguments?
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 are used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale.
Many points on the time scale are being revised, however, as the behavior of isotopes in the Earth’s crust is more clearly understood. Thus the graphic illustration of the geologic time scale, showing both relative time and radiometric time, represents only the present state of knowledge.
Badlands National Park, South Dakota. NPS photo by M. Geologists count back more than 4 billion years to the oldest Earth materials. Have you ever tried to count to a million? Counting once per second easy at the start, but tough when you reach the hundred-thousand mark , 24 hours per day, seven days per week no weekends off , it would take you 11 days, 14 hours to count to one million!
There are a thousand millions in a billion, so counting to a billion would take you approximately 32 years. Taking this one step further, it is not humanly possible to count to 4. To help comprehend the length of geologic time, some analogies are provided below. Age of Earth as a Ball of String If a piece of string an inch long about 2. A string representing all of recorded human history would be 1.
Geologic time scale
The table of geologic time spans presented here agrees with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geological Survey. Evidence from radiometric dating indicates that the Earth is about 4. The geological or deep time of Earth’s past has been organized into various units according to events which took place in each period. Different spans of time on the time scale are usually delimited by major geological or paleontological events, such as mass extinctions.
For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous—Tertiary extinction event, which marked the demise of the dinosaurs and of many marine species. Older periods which predate the reliable fossil record are defined by absolute age.
To help students understand the development of the geologic time scale. Also, to introduce students to the major time periods in earth’s history, as well as to the role fossils play in helping us understand this history. This lesson is based on an online booklet that provides an introduction to the.
Increasing temperature will increase molecular speed. An object with less massive molecules will have higher molecular speed at the same temperature. When kinetic temperature applies, two objects with the same average translational kinetic energy will have the same temperature. An important idea related to temperature is the fact that a collision between a molecule with high kinetic energy and one with low kinetic energy will transfer energy to the molecule of lower kinetic energy. Part of the idea of temperature is that for two collections of the same type of molecules that are in contact with each other, the collection with higher average kinetic energy will transfer energy to the collection with lower average kinetic energy.
We would say that the collection with higher kinetic energy has a higher temperature, and that net energy transfer will be from the higher temperature collection to the lower temperature collection, and not vice versa. Clearly, temperature has to do with the kinetic energy of the molecules, and if the molecules act like independent point masses, then we could define temperature in terms of the average translational kinetic energy of the molecules, the so-called ” kinetic temperature “.
The average kinetic energy of the molecules of an object is an important part of the concept of temperature and provides some useful intuition about what temperature is. If all matter just consisted of independently moving point masses that just experienced elastic collisions with each other, that would be an adequate picture of temperature. Internal or coordinated motions of molecules complicate the picture of temperature. Molecules for materials other than monoatomic noble gases like helium have the possibility of energy other than the translational kinetic energy of point masses.
Molecules can have rotational and translational kinetic energy and the molecules in periodic solids can have collective modes of motion that have energy. This complicates the idea of temperature because they affect the conditions under which energy would be transferred from one collection of molecules to another, and we want to hang onto the idea that if energy is spontaneously transferred from A to B, then A is at a higher temperature than B.
Geological time scale
Important We believe any unbiased reader will realize that we were fair with our treatment of the two models in the table above. Yet, although the theory of evolution matches the facts in some cases, evolution is still an unproven theory. By now, you may believe it should be your first choice also. Unlike many others that preceded us, we attempted to find a clear defense of evolution for two reasons: To keep from being accused of bias.
One of the very foundations of evolution and popular science today is the “geologic column.” This column is made up of layers of sedimentary rock that supposedly formed over millions and even billions of .
The Radiometric Dating Game Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years.
We are told that these methods are accurate to a few percent, and that there are many different methods. We are told that of all the radiometric dates that are measured, only a few percent are anomalous. This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points.
Since there doesn’t seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.
Geologic history of Earth
Hadean Eon The name says it all; a hellish period lasting some million years, when the Earth was subject to frequent bombardment by comets, asteroids, and other planetary debris. This era begins when a Mars-sized body struck the original Earth, pulverizing both, and reforming into the current Earth-moon binary. Gradually the molten Earth cools, outgassing of first atmosphere and oceans, bombardment by left-over planetesimal and debris.
The Hadean eon was characterized by extensive volcanism and formation of the first crust.
Geology: Geology, the fields of study concerned with the solid Earth. Included are sciences such as mineralogy, geodesy, and stratigraphy. An introduction to the geochemical and geophysical sciences logically begins with mineralogy, because Earth’s rocks are composed of minerals—inorganic elements or.
Early history[ edit ] In Ancient Greece , Aristotle BCE observed that fossils of seashells in rocks resembled those found on beaches — he inferred that the fossils in rocks were formed by living animals, and he reasoned that the positions of land and sea had changed over long periods of time. Leonardo da Vinci — concurred with Aristotle’s interpretation that fossils represented the remains of ancient life.
Steno argued that rock layers or strata were laid down in succession, and that each represents a “slice” of time. He also formulated the law of superposition, which states that any given stratum is probably older than those above it and younger than those below it. While Steno’s principles were simple, applying them proved challenging. Steno’s ideas also lead to other important concepts geologists use today, such as relative dating.
Over the course of the 18th century geologists realized that: Sequences of strata often become eroded, distorted, tilted, or even inverted after deposition Strata laid down at the same time in different areas could have entirely different appearances The strata of any given area represented only part of Earth’s long history The Neptunist theories popular at this time expounded by Abraham Werner — in the late 18th century proposed that all rocks had precipitated out of a single enormous flood.
John McPhee asserts that “as things appear from the perspective of the 20th century, James Hutton in those readings became the founder of modern geology”.
Geologic Time Scale
Contact Us Geologic Time Scale Humans subdivide time into useable units such as our calendar year, months, weeks, and days; geologists also subdivide time. They have created a tool for measuring geologic time, breaking it into useable, understandable segments. The geologic time scale grew out of necessity: No one person or expert committee proposed the geologic time scale used today.
A geologic era is a subdivision of geologic time that divides an eon into smaller units of time. The Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic (meaning “old life”, “middle life” and “recent life”) that represent the major stages in the macroscopic fossil eras are separated by catastrophic extinction boundaries, the P-T boundary.
Divisions of Geologic Time approved by the U. Geological Survey Geologic Names Committee, The chart shows major chronostratigraphic and geochronologic units. It reflects ratified unit names and boundary estimates from the International Commission on Stratigraphy Ogg, Map symbols are in parentheses. All other units are periods.
A geologic time scale is composed of standard stratigraphic divisions based on rock sequences and is calibrated in years Harland and others, Over the years, the development of new dating methods and the refinement of previous methods have stimulated revisions to geologic time scales. Advances in stratigraphy and geochronology require that any time scale be periodically updated.
Therefore, Divisions of Geologic Time, which shows the major chronostratigraphic position and geochronologic time units, is intended to be a dynamic resource that will be modified to include accepted changes of unit names and boundary age estimates.
High School Earth Science/Geologic Time Scale
For example, rock layers show the sequence of geological events, and the presence and amount of radioactive elements in rocks make it possible to determine their ages. Analyses of rock formations and the fossil record are used to establish relative ages. In an undisturbed column of rock, the youngest rocks are at the top, and the oldest are at the bottom.
Rock layers have sometimes been rearranged by tectonic forces; rearrangements can be seen or inferred, such as from inverted sequences of fossil types. The rock record reveals that events on Earth can be catastrophic, occurring over hours to years, or gradual, occurring over thousands to millions of years. Records of fossils and other rocks also show past periods of massive extinctions and extensive volcanic activity.
Geological time scale. The vast expanse of geological time has been separated into eras, periods, and epochs. The numbers included below refer to the beginnings of the division in which the title appears.
The time data from radiometric dating is taken from that source. The times are in millions of years. For examples that cover most of these time periods, see the outline of the Grand Canyon and Grand Staircase. Active Graphic Some descriptive information about the different divisions of geologic time is given below. The brief outline below draws from that material and elsewhere to provide a brief sketch of Earth history.
Note that the dates in millions of years are representative values. Research publications would give error bars for such division dates – it is not implied here that these boundaries are known to 3 or 4 significant digits. The division of the geologic column into different periods is largely based upon the varieties of fossils found, taken as indicators of a time period in Earth’s history. By the beginning of the Quaternary Period, most of the major plate tectonic movements which formed the North American continent had taken place, and the main modifications past that were those produced by glacial action and erosion processess.
Divisions of Geologic Time
Early history[ edit ] In Ancient Greece , Aristotle BCE observed that fossils of seashells in rocks resembled those found on beaches — he inferred that the fossils in rocks were formed by living animals, and he reasoned that the positions of land and sea had changed over long periods of time. Leonardo da Vinci — concurred with Aristotle’s interpretation that fossils represented the remains of ancient life. Steno argued that rock layers or strata were laid down in succession, and that each represents a “slice” of time.
Geologic history of Earth: Geologic history of Earth, evolution of the continents, oceans, atmosphere, and biosphere. The layers of rock at Earth’s surface contain evidence of the evolutionary processes undergone by these components of the terrestrial environment during the times at which each layer was formed. By studying.
Describe the five Principles of Stratigraphy and explain how each applies to interpreting geologic history of an area. Describe the geologic history of the Grand Canyon as interpreted using the Principles of Stratigraphy. Apply relative dating principles to a block diagram and interpret the sequence of geologic events. Explain what an isotope is and what alpha decay, beta decay, and electron capture are as mechanisms of radioactive decay.
Describe how radio-isotopic dating is accomplished and list four key isotopes used for doing it. Explain how carbon is formed in the atmosphere and how it is used in dating recent events. Explain how scientists know the numeric age of the Earth and other events in Earth history. Explain how sedimentary sequences can be dated using radio-isotope and other techniques.
What is a fossil? Describe ways by which fossils are preserved.