# Radioactive dating game phet answers

A swimming race illustrates the simple principles involved in measuring time. This swimmer is competing in a 1,500 metre race and we have an accurate, calibrated wristwatch. We note that at the instant the swimmer touches the edge of the pool our wristwatch reads 7:41 and 53 seconds. How long has the competitor taken to swim the 1,500 metre race?

When I have asked an audience this question they have looked at me incredulously and said, “Starting time?” You cannot know how long the swimmer took unless you knew the time on the wristwatch when the race started. Without the starting time it is impossible to establish the time for the race. Note: Impossible .

Actually, knowing the starting time is still not enough. During the race you have to watch the swimmer and count how many laps he has swum so you know that he has done 1,500 metres. And you have to check to make sure he touches the edge at the end of each lap. Without these observations you cannot be sure that the time is valid. That is why you need at least two, sometimes three judges to measure the time of the race to the standard needed to enter the record books.

It would make no difference how accurate or high-tech the wristwatch was. You could talk about the tiny quartz crystal and the piezoelectric effect used to provide a stable time base for the electronic movement. You could describe the atomic workings of the quartz oscillator and how it resonates at a specific and highly stable frequency, and how this is used to accurately pace a timekeeping mechanism.

But without reliable witnesses the accuracy of the watch makes no difference. You can only establish the time for the race if it was timed by two or more qualified eyewitnesses who observed the start, the progress and the finish.

This illustrates the whole problem with the radioactive dating of geological events. Those who promote the reliability of the method spend a lot of time impressing you with the details of radioactive decay, half-lives, mass-spectroscopes, etc. But they omit discussion of the basic flaw in the method: you cannot measure the age of a rock using radioactive dating because you were not present to measure the radioactive elements when the rock formed and you did not monitor the way those elements changed over its entire geological history.

If you check this educational page by the US Geological Society you will see that they spend all their time talking about the technicalities of radioactive decay. But they do not even mention the basic problem that you cannot know the radioactive concentrations that existed in the rock in the past.

Half-life (abbreviated t 1⁄2 ) is the time required for a quantity to reduce to half its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay . The term is also used more generally to characterize any type of exponential or non-exponential decay. For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the body. The converse of half-life is doubling time .

The original term, * half-life period* , dating to Ernest Rutherford 's discovery of the principle in 1907, was shortened to * half-life* in the early 1950s. [1] Rutherford applied the principle of a radioactive element's half-life to studies of age determination of rocks by measuring the decay period of radium to lead-206 .

Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation. The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed.

A half-life usually describes the decay of discrete entities, such as radioactive atoms. In that case, it does not work to use the definition that states "half-life is the time required for exactly half of the entities to decay". For example, if there are 3 radioactive atoms with a half-life of one second, there will not be "1.5 atoms" left after one second.

Instead, the half-life is defined in terms of probability : "Half-life is the time required for exactly half of the entities to decay * on average * ". In other words, the * probability* of a radioactive atom decaying within its half-life is 50%.

For example, the image on the right is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not * exactly* one-half of the atoms remaining, only * approximately* , because of the random variation in the process. Nevertheless, when there are many identical atoms decaying (right boxes), the law of large numbers suggests that it is a * very good approximation* to say that half of the atoms remain after one half-life.

There are various simple exercises that demonstrate probabilistic decay, for example involving flipping coins or running a statistical computer program . [2] [3] [4]

A two-hour special from the producers of "Making Stuff" Airing April 4, 2012 at 9 pm on PBS Aired April 4, 2012 on PBS

Where do nature's building blocks, called the elements, come from? They're the hidden ingredients of everything in our world, from the carbon in our bodies to the metals in our smartphones. To unlock their secrets, David Pogue, technology columnist and lively host of NOVA's popular "Making Stuff" series, spins viewers through the world of weird, extreme chemistry: the strongest acids, the deadliest poisons, the universe's most abundant elements, and the rarest of the rare—substances cooked up in atom smashers that flicker into existence for only fractions of a second.

It turns out that nature has concealed thousands of pounds of the stuff under billions of cubic feet of earth. By digging, these guys are hoping to strike it rich.

But that's not why I'm here. I'm on a quest to understand the basic building blocks of everyday matter. They're called the elements. These symbols represent the atoms that make up every single thing in our universe: 118 unique substances arranged on an amazing chart that reveals their hidden secrets to anyone who knows how to read it.

It's a journey that dives deep into the metals of civilization, marvels at the mysteries of the extremely reactive, reveals hidden powers and harnesses secrets of life, from hydrogen to uranium and beyond.

I'm starting with one of humanity's first elemental loves: gold; symbol Au. Like all elements, gold is an atom that gets its identity from tiny particles: positively charged protons in the nucleus, balanced by negatively charged electrons all around, plus neutrons, which have no charge at all.

Gold has been sought since ancient times, yet all the gold ever mined would fit into a single cube about 60 feet on a side. Gold is unique among the metals. It doesn't rust or tarnish. It's virtually indestructible, yet also soft and malleable. It was a sacred material to ancient people, and it's never lost its luster.

Many people assume that the dates scientists quote of millions of years are as reliable as our knowledge of the structure of the atom or nuclear power. And radioactive dating is so shrouded with mystery that many don’t even try to understand how the method works; they just believe it must be right.

But the basic concept of radioactive dating, sometimes called radiometric dating, is not difficult, especially since all of us regularly calculate how much time has passed: for example, since our birth, or since we started on a walk. A swimming race is a familiar situation that illustrates the simple principles involved in measuring time. Once we understand what we actually need to do we can apply the same principles to radioactive dating, and see if the methods do what they are claimed to do.

Picture a swimmer competing in a 1,500 metre race and an observer with an accurate wristwatch. We note that at the instant the swimmer touches the end of the pool our wristwatch reads 7:41 and 53 seconds. How long has the competitor taken to swim the race?

When I have asked an audience this question they have looked at me incredulously and said, “Starting time?” They realize that you cannot know how long the swimmer took unless you knew the time on the wristwatch when the race started. Keep that in mind when you think about working out the age of something. Without knowing the starting time it is impossible to establish the time for the race. Note: Impossible .

Actually, knowing the starting time is still not enough. During the race you have to watch the swimmer and count how many laps he has swum so you know that he has done 1,500 metres. And you have to check to make sure he touches the end for each lap. Without these observations you cannot be sure that the time is valid. That is why you need three timekeepers to independently record the times during the race to meet the standard needed to enter the record books.

Would it make any difference if the watch we were using was more accurate? Absolutely not! You could talk about the tiny quartz crystal and the piezoelectric effect used to provide a stable time base for the electronic movement. You could describe the atomic workings of the quartz oscillator and how it resonates at a specific and highly stable frequency, and how this is used to accurately pace a timekeeping mechanism.

The fact is that you can only establish the time for the race if it was timed by two or more reliable eyewitnesses who observed the start , the progress and the finish of the race.

# Radioactive dating anomalies - creation.com

Half-life (abbreviated t 1⁄2 ) is the time required for a quantity to reduce to half its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay . The term is also used more generally to characterize any type of exponential or non-exponential decay. For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the body. The converse of half-life is doubling time .

The original term, * half-life period* , dating to Ernest Rutherford 's discovery of the principle in 1907, was shortened to * half-life* in the early 1950s. [1] Rutherford applied the principle of a radioactive element's half-life to studies of age determination of rocks by measuring the decay period of radium to lead-206 .

Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation. The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed.

A half-life usually describes the decay of discrete entities, such as radioactive atoms. In that case, it does not work to use the definition that states "half-life is the time required for exactly half of the entities to decay". For example, if there are 3 radioactive atoms with a half-life of one second, there will not be "1.5 atoms" left after one second.

Instead, the half-life is defined in terms of probability : "Half-life is the time required for exactly half of the entities to decay * on average * ". In other words, the * probability* of a radioactive atom decaying within its half-life is 50%.

For example, the image on the right is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not * exactly* one-half of the atoms remaining, only * approximately* , because of the random variation in the process. Nevertheless, when there are many identical atoms decaying (right boxes), the law of large numbers suggests that it is a * very good approximation* to say that half of the atoms remain after one half-life.

There are various simple exercises that demonstrate probabilistic decay, for example involving flipping coins or running a statistical computer program . [2] [3] [4]