What can radiometric dating tell us about the age of rocks that the Law of whereas the Law of Superposition can only be used to determine the relative age . Oct 27, Thus, the “ages” assigned to rocks on the basis of radiometric dating are not You cannot tell when a given potassium atom will “pop” into.
Answer the following questions as you navigate through Understanding Geologic Time. How is relative age different from the actual date of an event? Relative age only tells us the order in which events occurred, from the earliest to the most recent. Knowing the actual date of an event allows us to say exactly how old something is or how long ago it actually took place. What can radiometric dating tell us about the age of rocks that the Law of Superposition cannot? Radiometric dating tells us how old the rocks are ys the Law of Superposition can only be used to determine the abou age 3.
Creationists would generally agree with the above methods and use them in their geological work. From his research, our evolutionary geologist may have discovered that other geologists believe that Sedimentary Rocks A are million years old and Sedimentary Rocks B are 30 million years old.
Creationists do not agree with these ages of millions of years because of the assumptions they are based on. On his return, he sends his sample to the laboratory for dating, and after a few weeks receives the lab report. The only foolproof method for determining the age of something is based on eyewitness reports and a written record.
Let us imagine that the date reported by the lab was Our geologist would be very happy with this result. He would say that the date represents the time when the volcanic lava solidified.
Such an interpretation fits nicely into the range of what he already believes the age to be. In fact, he would have been equally happy with any date a bit less than million years or a bit more than 30 million years.
They would all have fitted nicely into the field relationships that he had observed and his interpretation of them. What would our geologist have thought if the date from the lab had been greater than million years, say Would he have concluded that the fossil date for the sediments was wrong?
Not likely. Would he have thought that the radiometric dating method was flawed? Instead of questioning the method, he would say that the radiometric date was not recording the time that the rock solidified. He may suggest that the rock contained crystals called xenocrysts that formed long before the rock solidified and that these crystals gave an older date.
The error is not the real error The convention for reporting dates e. In other words, the age should lie between However, this error is not the real error on the date. It relates only to the accuracy of the measuring equipment in the laboratory. Even different samples of rock collected from the same outcrop would give a larger scatter of results. These include the assumption that decay rates have never changed. In fact, decay rates have been increased in the laboratory by factors of billions of times.
Return to text. Vardiman, L. How old are rocks? Relative dating Relative dating is used to determine the relative order of past events by comparing the age of one object to another.
This determines where in a timescale the object fits without finding its specific age; for example you could say you're older than your sister which tells us the order of your birth but we don't know what age either of you are. There are a few methods of relative dating, one of these methods is by studying the stratigraphy. Stratigraphy is the study of the order of the layers of rocks and where they fit in the geological timescale. This method is most effective for studying sedimentary rocks.
Cross dating is a method of using fossils to determine the relative age of a rock. Fossil remains have been found in rocks of all ages with the simplest of organisms being found in the oldest of rocks. The more basic the organism the older the rock is. This practice supports the theory of evolution which states that simple life forms gradually evolve over time to form more complex ones. Studying the layers of rock or strata can also be useful.
Layers of rock are deposited sequentially. If a layer of rock containing the fossil is higher up in the sequence that another layer, you know that layer must be younger in age.
This can often be complicated by the fact that geological forces can cause faulting and tilting of rocks. Absolute Dating Absolute dating is used to determine a precise age of a rock or fossil through radiometric dating methods. This uses radioactive minerals that occur in rocks and fossils almost like a geological clock. So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
The atoms in some chemical elements have different forms, called isotopes. These isotopes break down at a constant rate over time through radioactive decay. By measuring the ratio of the amount of the original parent isotope to the amount of the daughter isotopes that it breaks down into an age can be determined. We define the rate of this radioactive decay in half-lives.