Earth Science: Geologic Ages and Dating Techniques

Aristotle thought the earth had existed eternally. Roman poet Lucretius, intellectual heir to the Greek atomists, believed its formation must have been relatively recent, given that there were no records going back beyond the Trojan War. The Talmudic rabbis, Martin Luther and others used the biblical account to extrapolate back from known history and came up with rather similar estimates for when the earth came into being. Within decades observation began overtaking such thinking. In the s Nicolas Steno formulated our modern concepts of deposition of horizontal strata. He inferred that where the layers are not horizontal, they must have been tilted since their deposition and noted that different strata contain different kinds of fossil. This position came to be known as uniformitarianism, but within it we must distinguish between uniformity of natural law which nearly all of us would accept and the increasingly questionable assumptions of uniformity of process, uniformity of rate and uniformity of outcome. That is the background to the intellectual drama being played out in this series of papers. It is a drama consisting of a prologue and three acts, complex characters, and no clear heroes or villains.

How Old Is Earth?

Earth is about 4. Geologists divide this age into major and minor units of time that describe the kinds of geological processes and life forms that existed in them. Earth’s geologic record was formed by constant change, just like those that occur routinely today. Though some events were catastrophic, much of Earth’s geology was influenced by normal weather, erosion, and other processes spread over very long geologic ages.

Accurate dating of the geologic ages is fundamental to the study of geology and paleontology, and provides important context to the life sciences, meteorology, oceanography, geophysics, and hydrology. In the mid-seventeenth century, James Ussher — , the Archbishop of Ireland, compiled a chronology of Earth by adding up the generations named in the Bible.

These dating techniques, which are firmly grounded in physics and are known collectively as radiometric dating, are used to measure the last.

Students, particularly Young-Earth Creationists, may come in with misconceptions about how the age of the Earth and of various parts of the fossil record were determined. Your Account. Explore Teaching Examples Provide Feedback. Teaching about Radiometric Dating Students, particularly Young-Earth Creationists, may come in with misconceptions about how the age of the Earth and of various parts of the fossil record were determined. For example, they may assume that the whole geologic timeline is based on radiocarbon dating, which only gives reliable results for dates back to 40, years before present Low, personal communication.

Others will argue that decay rates could have changed Wise, , or that God could have changed them, which might result in too-old dates. The former argument is flawed because many radiometric dates are broadly supported by other estimates of change, such as tree rings and varved sediments for radiocarbon with some discrepancies, but still leaving the Earth far more than 6, years old. The second is not a scientific argument. If supernatural forces are changing the laws of physics while we’re not looking, no form of science, “creation science” or otherwise, can prove or disprove it.

Students may also be aware that bad assumptions and contamination can result in inaccurate radiometric dates. This is very true! This doesn’t change the enormous number of consistent radiometric dates for many of the important events recorded by the Earth system.

Age of Earth

Planet Earth doesn’t have a birth certificate to record its formation, which means scientists spent hundreds of years struggling to determine the age of the planet. So, just how old is Earth? By dating the rocks in Earth’s ever-changing crust, as well as the rocks in Earth’s neighbors, such as the moon and visiting meteorites, scientists have calculated that Earth is 4.

Many other methods have been used to date the Earth, with many different sets of radioactive nuclides (and other methods). They are all.

A relative age simply states whether one rock formation is older or younger than another formation. The Geologic Time Scale was originally laid out using relative dating principles. The geological time scale is based on the the geological rock record, which includes erosion, mountain building and other geological events. Over hundreds to thousands of millions of years, continents, oceans and mountain ranges have moved vast distances both vertically and horizontally.

For example, areas that were once deep oceans hundreds of millions of years ago are now mountainous desert regions. How is geological time measured? The earliest geological time scales simply used the order of rocks laid down in a sedimentary rock sequence stratum with the oldest at the bottom. However, a more powerful tool was the fossilised remains of ancient animals and plants within the rock strata. After Charles Darwin’s publication Origin of Species Darwin himself was also a geologist in , geologists realised that particular fossils were restricted to particular layers of rock.

This built up the first generalised geological time scale. Once formations and stratigraphic sequences were mapped around the world, sequences could be matched from the faunal successions. These sequences apply from the beginning of the Cambrian period, which contains the first evidence of macro-fossils. Fossil assemblages ‘fingerprint’ formations, even though some species may range through several different formations. This feature allowed William Smith an engineer and surveyor who worked in the coal mines of England in the late s to order the fossils he started to collect in south-eastern England in

How are the ages of the Earth and universe calculated?

The remainder of the year corresponds to global overshoot. Global Ecological Footprint and biocapacity metrics are calculated each year in the National Footprint and Biocapacity Accounts. Using UN statistics, these accounts incorporate the latest data and the most updated accounting methodology the National Footprint and Biocapacity Accounts Edition feature data. The annual dates of Earth Overshoot Day are recalculated accordingly.

Consequently, it is inaccurate to simply look at media accounts from previous years to determine past Earth Overshoot Days.

A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods. More slowly decaying isotopes are useful for longer periods of time, but less accurate in absolute years.

Skip to main page content Skip to secondary navigation Skip to summary access keys list. Show: All Earth and Space Science exemplars. This annotated exemplar is intended for teacher use only. The student work shown does not always represent a complete sample of what is required. Selected extracts are used, focused on the grade boundaries, in order to assist assessors to make judgements at the national standard. For Excellence, the student needs to comprehensively investigate the evidence related to dating geological event s.

This student has conducted a comprehensive investigation by dating the Park Volcanics group in south-east Southland. Relevant dating techniques have been investigated, justifying those selected 1. A final age has been cross-correlated using 3 techniques 2. For a more secure Excellence, the student could explain comprehensively how the Rb-Sr dating technique works, its half-life and decay method and why it was selected for cross-correlation.

This is true in the Park Volcanics. For Merit, the student needs to investigate in depth the evidence related to dating geological event s. This involves explaining, in detail, how a range of key evidence contributes to the understanding of the dating of geological event s.

Geochronology

You may have heard that the Earth is 4. This was calculated by taking precise measurements of things in the dirt and in meteorites and using the principles of radioactive decay to determine an age. This page will show you how that was done. Radioactive nuclides decay with a half-life. If the half-life of a material is years and you have 1 kg of it, years from now you will only have 0.

While there are numerous experimental methods used to determine geologic ages, the most frequently employed technique is radiometric dating.

Dating , in geology , determining a chronology or calendar of events in the history of Earth , using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques. These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events.

Radiometric dating and certain other approaches are used to provide absolute chronologies in terms of years before the present. The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere. Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled. This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.

For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built. Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence. Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information.

A coin, vessel, or other common artifact could link two archaeological sites, but the possibility of recycling would have to be considered. It should be emphasized that linking sites together is essential if the nature of an ancient society is to be understood, as the information at a single location may be relatively insignificant by itself. Similarly, in geologic studies, vast quantities of information from widely spaced outcrops have to be integrated. Some method of correlating rock units must be found.

How Do We Know the Earth Is 4.6 Billion Years Old?

The same was long true of the cosmos. The ancient Greeks Eratosthenes and Aristarchus measured the size of the Earth and Moon, but could not begin to understand how old they were. With space telescopes, we can now even measure the distances to stars thousands of light-years away using parallax, the same geometric technique proposed by Aristarchus, but no new technology can overcome the fundamental mismatch between the human lifespan and the timescales of the Earth, stars, and universe itself.

The following table shows close approaches to the Earth by near-Earth objects Close-Approach (CA) Date: Date and time (TDB) of closest Earth approach.

JavaScript is disabled in your browser. Enable it if you want to make full use of the features on our website. How old is Earth? In secular circles, the age is believed to be around 4. This number is used so often that most people accept it as a scientific fact. Radiometric dating is an important key to the deep-time age estimate for Earth. Various methods use radioactive elements and their decay products to date rock samples from around the world in the hundreds of millions of years.


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