Age Dating the Earth
Akio Makishima, in Origins of the Earth, Moon, and Life, Using dating methods using radioactive isotopes, time-criteria can be given in theoretical models. that the dating methods used to establish the “old Earth” are flawed in many respects. Overview. Fossil remains are found in sedimentary rock layers. Layers of. Using relative and radiometric dating methods, geologists are able to answer the Second, it is possible to determine the numerical age for fossils or earth.
According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3. Huxleyattacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. The physicist Hermann von Helmholtz in and astronomer Simon Newcomb in contributed their own calculations of 22 and 18 million years respectively to the debate: However, they assumed that the Sun was only glowing from the heat of its gravitational contraction.
The process of solar nuclear fusion was not yet known to science. In John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity.
Charles Darwin 's son, the astronomer George H. Darwinproposed that Earth and Moon had broken apart in their early days when they were both molten. He calculated the amount of time it would have taken for tidal friction to give Earth its current hour day. His value of 56 million years added additional evidence that Thomson was on the right track. Radiometric dating Overview By their chemical nature, rock minerals contain certain elements and not others; but in rocks containing radioactive isotopes, the process of radioactive decay generates exotic elements over time.
By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated.
Convective mantle and radioactivity InThomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. Kelvin calculated the age of the Earth by using thermal gradientsand he arrived at an estimate of about million years. InJohn Perry produced an age-of-Earth estimate of 2 to 3 billion years using a model of a convective mantle and thin crust. The discovery of radioactivity introduced another factor in the calculation.
After Henri Becquerel 's initial discovery inMarie and Pierre Curie discovered the radioactive elements polonium and radium in ; and inPierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth. These had assumed that the original heat of the Earth and Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished.
George Darwin and John Joly were the first to point this out, in Please help improve this article by adding citations to reliable sources.
Unsourced material may be challenged and removed. October Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.
Ernest Rutherford in Ernest Rutherford and Frederick Soddy jointly had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process.
They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a " half-life ", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product". Some radioactive materials have short half-lives; some have long half-lives.
Age of the Earth - Wikipedia
Uranium and thorium have long half-lives, and so persist in Earth's crust, but radioactive elements with short half-lives have generally disappeared. This suggested that it might be possible to measure the age of Earth by determining the relative proportions of radioactive materials in geological samples. In reality, radioactive elements do not always decay into nonradioactive "stable" elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a stable element.
The Paleozoic is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous which is sometimes divided into the Mississippian and Pennsylvanian eras and Permian periods.
Each of these is further divided into several epochs, some named for places where their major characteristics were discovered, others simply divided into early, middle, and late epochs. During the Paleozoic erainsects, plants, the first vertebrate animals, amphibians, reptiles, fish, sharks, and corals all appeared. Often, it is the changes in the kinds of animals and plants that are used to decide boundaries between the different periods. Despite the emphasis on life in describing the various ages of the Paleozoic, geologic processes were still under way.
Supercontinents formed and broke apart, several ice ages advanced and retreated, temperatures fluctuated, and sea levels rose and fell. These diverse processes influenced the many changes in life that are recorded in the fossils of the era—coal deposits in Europe laid down during the Carboniferous period are one of its more famous features. At the end of the Paleozoic eraa disastrous event known as the Permian-Triassic extinction led to the destruction of almost all Paleozoic species.
Though there have been efforts to link this extinction to a meteorite impact, no convincing evidence of a large enough collision during this time period has been found. Dinosaurs appeared during the Mesozoic era. The names of the periods in the Mesozoic era may sound familiar: Triassic, Jurassic, and Cretaceous. During this million-year era, all the familiar dinosaurs such as triceratops, tyrannosaurus, stegosaurus, diplodocus, and apatosaurus flourished at different times. Some modern animals have ancestors that first appeared during the Mesozoic era, including birds, crocodiles, and mammals.
Plants continued to develop, and the first flowering plants appeared. The end of the Mesozoic era can be seen clearly in some rock layers. Known as the K-T Cretaceous-Tertiary boundary, this dark line of sediment is rich in the element iridium.
Another massive extinction of species occurred at this time, possibly because of one or more meteorite impacts along with a period of intense volcanic activity. This would have decreased the amount of sunlight reaching Earth's surface, killing plants and, eventually, animals. Not all geologists and paleontologists are convinced that the K-T extinction was a catastrophic event; some argue that it occurred over a few million years after slower climate changes.
The Cenozoic erathe current era of geologic time, is divided into the Paleogene and Neogene periods, and further into the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene epochs. During the Cenozoic, the supercontinent of Gondwana broke apart, and the continents reached their current positions.
Several ice ages occurred, and the poles became ice-covered. The first mammals began to flourish in the Paleocene; the first apes appeared in the Miocene; and the first human ancestors in the Pliocene.
Modern humans, along with large animals such as mammoths and wooly rhinoceroses, appeared in the Pleistocene. The Holocene epochcurrently ongoing, began with the end of the last ice age, less than 10, years ago.
Though this vast span of time was largely understood by the end of the nineteenth century, geologists, paleontologists, and scientists of other disciplines were still curious about Earth's absolute ageusing different approaches to tackle the problem. In the s William Thomson —more commonly known as Lord Kelvin, applied his theories of thermodynamics to determine Earth's age.
He surmised that Earth was between 20 and 40 million years old by calculating the time it should take for it to cool from a liquid to a solid. Though his calculations and some of his assumptions were correct, he failed to account for heat added by radioactivity. Around the turn of the twentieth century, Irish geologist John Joly — estimated Earth's age by analyzing the salt content of the seas. He then assumed that the oceans had started off as freshwater, and that all the salt had washed into them from the land.
This relied on the assumption that the rate of salt coming into the oceans was constant and that no salt had ever been removed from the seas. By this calculation he arrived at an age of about million years. Scientists needed a method that relied on something measurable over Earth's entire lifespan. In rocks older than about million years, it becomes impossible to use fossils to calculate their age because very few, if any, exist in these rocks.
There are, however, a number of naturally radioactive elements that have been decaying since the formation of Earth. With the discovery of radiation and the calculation of half-lives in the twentieth century it finally became possible to determine the age of Earth's oldest rocks.
Radioactive decay is the spontaneous change in the nucleus of an element by the escape of a proton or neutron. Once a particle escapes the nucleus of an atom, it becomes a different isotope of the same element, or sometimes a different element altogether. The ratio of the original parent element to the daughter element produced by decay determines how long the element has been decaying.
The half-life of an isotope is the amount of time it takes for half of the sample to decay. InNew Zealand -born British physicist Ernest Rutherford — discovered that uranium and thorium decayed into isotopes of lead. By Bertram Boltwood —an American chemist studying radioactive materials, had calculated the age of certain rocks based on analysis of their radioactivity.
Radiometric dating, a well-regarded way to establish the age of rocks, is still based on the same principles laid out by Rutherford and Boltwood. It assumes that the half-lives of elements do not change over time, and that the sample has not been contaminated by the addition or removal of radioactive material.
Zirconium crystals are usually analyzed because they trap uranium in their structure. Analyzing the decay of uranium to lead is useful because the half-life of uranium is million years. Even longer dates can be measured with potassium-to-argon decay, with a half-life of 1. Carbon dating is useful for measuring very short ages on the geologic time scale. With a half-life of 5, years, carbon decay is useful for measuring dates up to about 70, years. This makes the method particularly useful for dating samples from the Holocene and late Pleistocene epochs.
Modern Cultural Connections Radiometric dating is the key to developing and understanding an absolute time scale of Earth and its geologic ages.
When geological events, rock formations, and individual species can be placed accurately in time, it becomes possible to understand their relationships to each other and to events and circumstances present today. Using radiometric techniques, the oldest dated minerals 4.
One problem with earth dating is that the original earth surface is assumed to have eroded long ago. But assuming the earth was formed at the time of the rest of our solar system, then recovered moon rock and meteorites can also be used to estimate the age of the earth. These estimates give 4. Non-radiometric Dating These techniques utilize the physical parameters of the earth, such as ice cores, annual lake sediments, and astronomical cycles.
Ice cores from Greenland and Antarctica show annual layers varves and can be traced up to about 40, years before the layers become too thin due to compaction. Similarly, annual lake sediments can be used to estimate relative age and conventional interpretation for the Green River varves suggests they have been formed over some 20 million years.
This implies the earth is at least 20 million years old.
Age Dating the Earth
Astronomical cycles can also be used to measure relative age. The earth precesses wobbles like a spinning top around the sun in a series of cycles. These cycles affect sunlight and hence long-term can form layers in rock. In some cases these astronomical cycles in rock appear to have been laid down over some 25 million years and radiometric dating puts the absolute age of the rock at some million years.
Dating Anomalies Here we outline a few dating methods or 'clocks' that present a dating anomaly when referenced to the widely accepted OE age of 4. They appear to be inconsistent with an old earth.
Radio Carbon C Dating At the outset we note C cannot be used to directly date the earth for the simple reason that the unstable C isotope has a half-life of just 5, years. In other words, half of the radioactive isotope in a sample would have decayed to Nitrogen N in just 5, years.
C dating of carbon-bearing materials is therefore limited to roughly 50, years. But YE scientists point out some anomalies in relation to C and a very old earth. For instance, measurable amounts of C have been found in fossil material, such as coal traditionally Carboniferous period c mya. In fact, organic samples from every portion of the Phanerozoic record spanning the last million years on OE dating show detectable amounts of C The implication is that this organic material was either contaminated by new C, or it was buried much more recently and OE dating methods are suspect.
Ocean Measurements One early approach was based upon ocean salinity [John Joly, 's]. This assumed the ocean was initially pure water and that it's salinity was derived from continental erosion.
The technique gave 90 million years, but took no account of the non-constant erosion rate, or the loss and recycling of salt, or the fact that salt is obtained from other sources as well as continents. More recently, work has been done on ocean sediments [S. Nevins, Institute for Creation Research]. This suggests that, given the current annual rates of erosion some Clearly, this seems incompatible with an ocean billions of years old.
However, this may be a simplistic computation since there is Sediment Recycling as sediments accumulate and cause continental plates to collide, resulting in land uplift and subsequent errosion. Earth's Magnetic Field The Earth's magnetic field is thought to arise from circulating electic currents in the Earth's molten metalic core, and scientists agree that the field is weakening. At the current rate of decline it could take just 1, years to disappear, with increasing effects upon the electronic systems of satellites and spacecraft.
Magnetic field decrease applies to other planets. For instance, recent satellite measurements show that Mercury's magnetic field is rapidly decaying and YE Creationists claim this indicates a young field. OE scientists believe that a weakened magnetic field could herald a new magnetic pole reversal.
Magnetic pole reversals are rebutted by YE creationists. Instead they claim that the field decrease can be used as a clock to date the earth since it has been decaying since the origin of the earth. Taking the half-life of the decaying magnetic moment at yearsthe field is now only about one third as strong as it was at the time of Christ. Working further back in time, the value of the earth's magnetic field approaches that of a magnetic star at 10, years ago. Since this would need a huge nuclear power source, it seems magnetic field decay places an upper age limit on the earth of the order of 10, years.
Whilst the rigour of this YE theory is disputed see talkoriginsrecent spacecraft observations have confirmed its planetary magnetic predicions made in ! Atmospheric Helium The decay of uranium and thorium isotopes results in a net build-up of Helium-4 atoms in the atmosphere. It is claimed to be increasing at an annual rate of 3. From these figures and known decay rates, it can be shown that the current amount of atmospheric Helium can be generated in just 11, years not billions of years.
Short-Period Comets Short-period comets orbit the sun in less than years the Halley comet orbits about every 76 years.
Dating Techniques - humans, body, used, process, Earth, life, plants, form, energy
Each time they come close to the sun they lose material the comet tail and disintegrate. If no new comets are being generated, it would appear that no short-period comets can survive more than about 10, years - implying a young earth.
This claim is countered by the fact that the origin of short-period comets is still uncertain and that there may be a source of short-period comets e. Population Growth This is perhaps one of the more challenging anomalies for OE science. It is claimed that Homo sapiens appeared sometoyears ago. But doesn't it seem strange that after more thanyears earth's population is still only 7 billion?
After all, the population increased from 1 billion in to 7 billion in - a span of just years!