Carbon-14 has a half-life of about 5,730 years — which means that 5,730 years after an organism dies, half of the isotope present in the original sample will have decayed. After another 5,730 years, half of the carbon-14 that remained has decayed (leaving one-fourth of the amount from the original sample). Eventually, after 50,000 years or so (or almost nine half-lives), so little carbon-14 remains that the sample can’t be reliably dated. At subduction zones along continental margins, oceanic crust is pulled into the mantle and melted. Streams and rivers carry weathered rocks to lowlands and the ocean, depositing stones, mud, and sand along the way. Over geologic time, accumulated sediment can become compressed to form rock or pulled into the mantle to be recycled.
What are the four ways to understand the Earth’s age according in the film?
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth’s surface is moving and changing. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils. Plants extract carbon from the carbon dioxide in earth’s atmosphere, and since a small fraction of that carbon is c-14, plants do contain some c-14.
To see the fission tracks, the mineral surface is polished, etched with acids, and examined with an electron microscope. An effective way to measure the uranium concentration is to irradiate the sample in a nuclear reactor and produce comparative artificial tracks by the induced fission of 235U. We must also note that rocks are not completely solid, but porous.
The chemical analysis of rocks and minerals
Similarly, some rocks return radiometric “ages” twice as old as the accepted age for earth. Geologists now use radioactivity to establish the age of certain rocks and fossils. If that had happened, Darwin’s ideas would have been refuted and abandoned. Instead, radioactive dating indicates that Earth is about 4.5 billion years old—plenty of time for evolution and natural selection to take place. In this short paper I have briefly described 4 examples of radiometric dating studies where there is both internal and independent evidence that the results have yielded valid ages for significant geologic events.
Creationists seem to think that a few examples of incorrect radiometric ages invalidate all of the results of radiometric dating, but such a conclusion is illogical. Even things that work well do not work well all of the time and under all circumstances. Try, for example, wearing a watch that is not waterproof while swimming.
As water seeps into the remains, the minerals in the water fill the gaps in the bones, solidifying into a crystalline structure that eventually replaces the organic material. By the time minerals form a fossil, they are no longer “fresh”—the uranium inside has already been decaying for millions of years. Attempting to date one directly would yield a false result—much older than the organism itself. As a result, scientists must “rely on the geologic formations that are around or adjacent to the fossils” to calculate their age, Gibson explains. Because fossils are usually found in sedimentary rock layers, paleontologists can date them by examining the minerals above or below the sedimentary rock.
Radiometric Dating
In Morocco, paleontologists excavated the fossils of a dinosaur that roamed Earth 168 million years ago. When examining remnants from the past, experts use radiometric dating, a versatile technique that involves counting radioactive atoms of certain elements that are still present in a sample. The particular elements studied, as well as the details of check it out the process, depend on the approximate age of the object that scientists hope to date. The rate of isotope decay is very consistent, and is not effected by environmental changes like heat, temperature, and pressure. For example, sometimes it is possible for a small amount of new “parent” isotopes to be incorporated into the object, skewing the ratio.
A basic way to express the rate of radioactive decay is called the half-life. This equals the length of time needed for 50% of a quantity of radioactive material to decay. Unstable radioactive isotopes called parent elements become stable elements called daughter elements. In the Cretaceous Period, a large meteorite struck the earth at a location near the present town of Manson, Iowa. The heat of the impact melted some of the feldspar crystals in the granitic rocks of the impact zone, thereby resetting their internal radiometric clocks.
As it turns out, there is compelling evidence that the half-lives of certain slow-decaying radioactive elements were much smaller in the past. This may be the main reason why radiometric dating often gives vastly inflated age estimates. Such techniques have had an enormous impact on scientific knowledge of Earth history because precise dates can now be obtained on rocks in all orogenic belts ranging in age from the early Archean to the early Neogene . The oldest known rocks on Earth, estimated at 4.28 billion years old, are the faux amphibolite volcanic deposits of the Nuvvuagittuq greenstone belt in Quebec, Canada.
It is useful for dating very old igneous and metamorphic rocks and also meteorites and other cosmic fragments. However, there is a limited range in Sm-Nd isotopes in many igneous rocks, although metamorphic rocks that contain the mineral garnet are useful as this mineral has a large range in Sm-Nd isotopes. This technique also helps in determining the composition and evolution of the Earth’s mantle and bodies in the universe. This technique developed in the late 1960s but came into vogue in the early 1980s, through step-wise release of the isotopes. This technique uses the same minerals and rocks as for K-Ar dating but restricts measurements to the argon isotopic system which is not so affected by metamorphic and alteration events. Some do not change with time and form stable isotopes (i.e. those that form during chemical reactions without breaking down).