How can scientists determine the age of the earth

Related : What's the speed of Earth around the sun? Scientists have made several attempts to date the planet over the past years. They've attempted to predict the age based on changing sea levels, the time it took for Earth or the sun to cool to present temperatures and the salinity of the ocean. As the dating technology progressed, these methods proved unreliable; for instance, the rise and fall of the ocean was shown to be an ever-changing process rather than a gradually declining one.

And in another effort to calculate the age of the planet, scientists turned to the rocks that cover its surface. However, because plate tectonics constantly changes and revamps the crust, the first rocks have long since been recycled, melted down and reformed into new outcrops.

Scientists also must battle an issue called the Great Unconformity, which is where sedimentary layers of rock appear to be missing at the Grand Canyon, for example, there's 1. There are multiple explanations for this uncomformity; in early , one study suggested that a global ice age caused glaciers to grind into the rock , causing it to disintegrate.

Plate tectonics then threw the crushed rock back into the interior of the Earth, removing the old evidence and turning it into new rock. In the early 20th century, scientists refined the process of radiometric dating.

Earlier research had shown that isotopes of some radioactive elements decay into other elements at a predictable rate.

By examining the existing elements, scientists can calculate the initial quantity of a radioactive element, and thus how long it took for the elements to decay, allowing them to determine the age of the rock. But rocks older than 3. Greenland boasts the Isua supracrustal rocks 3. Samples in Western Australia run 3. Research groups in Australia found the oldest mineral grains on Earth. These tiny zirconium silicate crystals have ages that reach 4.

Their source rocks have not yet been found. Meanwhile, scientists have also found 7-billion-year-old stardust on Earth. Stratigraphy compares the configuration of layers of rock or sediment in order to determine how old each layer is in relation to one another. This technique can reveal which layers are older or which events happened before others if the layers of sediment have remained in sequential order. Layers can be rearranged, bent, or contain inconsistencies. However, stratigraphy yields no exact age for those layers or events.

Relative dating did not give scientists the exact number they were looking for. However, it did suggest that the Earth was most likely billions of years old, and not just millions as was previously thought. Determining Absolute Age of Rocks Advances in chemistry, geology and physics continued, and in the early to mids, scientists found a method to determine the absolute age of a rock or mineral sample.

The absolute age of a sample is its age in years. This method of determining absolute age is called radiometric dating , and it involves the decay, or breakdown, of radioactive elements.

Using radiometric dating, scientists can determine the actual age of a rock. Radiometric dating requires an understanding of isotopes. Isotopes are different forms of the same element, which have a different number of neutrons. Neutrons are tiny particles inside the nucleus , or core, of an atom.

The isotopes of unstable radioactive elements are called parent isotopes. They decay, or break down, into other, more stable elements called daughter isotopes.

They do this in a predictable way in a certain amount of time called a half-life. The half-life of an element is the amount of time required for exactly half of a quantity of that element to decay. Scientists can measure the number of parent isotopes that are left in a sample.

They compare this to the number of daughter isotopes that are in the sample. This comparison is called a ratio. Using the half-life, they can calculate how long it would take for that number of daughter isotopes to form.

Using the ratio and the half-life, they can determine the age of a rock sample. Radiometric Dating Zeroes in on Earth's Age One problem with this approach to dating rocks and minerals on Earth is the presence of the rock cycle. During the rock cycle, rocks are constantly changing forms. Old rocks are destroyed as they slide back into the planet, and new rocks form when lava cools and solidifies. The first rocks that formed on Earth are no longer here, and this makes finding an exact age for the planet difficult.

The oldest rocks that have been found are about 3. Nevertheless, by the late 19th century the geologists included here had reached a consensus for the age of the earth of around million years. Having come that far, they were initially quite reluctant to accept a further expansion of the geologic timescale by a factor of 10 or more.

And we should resist the temptation to blame them for their resistance. Radioactivity was poorly understood. Different methods of measurement such as the decay of uranium to helium versus its decay to lead sometimes gave discordant values, and almost a decade passed between the first use of radiometric dating and the discovery of isotopes, let alone the working out of the three separate major decay chains in nature.

The constancy of radioactive decay rates was regarded as an independent and questionable assumption because it was not known—and could not be known until the development of modern quantum mechanics—that these rates were fixed by the fundamental constants of physics.

It was not until , when under the influence of Arthur Holmes, whose name recurs throughout this story the National Academy of Sciences adopted the radiometric timescale, that we can regard the controversy as finally resolved. Critical to this resolution were improved methods of dating, which incorporated advances in mass spectrometry, sampling and laser heating. The resulting knowledge has led to the current understanding that the earth is 4. That takes us to the end of this series of papers but not to the end of the story.

As with so many good scientific puzzles, the question of the age of the earth resolves itself on more rigorous examination into distinct components. Such questions remain under active investigation, using as clues variations in isotopic distribution, or anomalies in mineral composition, that tell the story of the formation and decay of long-vanished short-lived isotopes. Isotopic ratios between stable isotopes both on the earth and in meteorites are coming under increasingly close scrutiny, to see what they can tell us about the ultimate sources of the very atoms that make up our planet.

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