so who wants to date an old fossil anyway?

Ask any evolutionary scientist how they can prove evolution occurred and they will tell you “the proof is in the fossil record.” But what exactly is a fossil anyway, and how does science know how old they are? Fossils are not bones; they are imprints of bones, that were covered quickly with mud (usually), and over a period of 20 to 200 years, as water percolated through the ground, removed the soluble organic material and replaced it with water born minerals. There are more than half a dozen different ways to create a fossil, petrifaction, lithifaction, mineralization, etc. and, almost never do you actually find a bone fragment. So with no organic material to find, these imprints cannot be dated by using carbon 14 (although even this often unreliable would prove the subject no more than several thousand years old). So how are they dated? Let’s take a look at how science is able to find these amazingly accurate dates (this is called geochronology) for these long expired individuals.

OK watch this closely, there is nothing up my sleeve. Upon locating a new fossil find, one must then look for two other things in the same general area. First you need to find what is called an index fossil, and you will need to find an igneous rock. Index fossils are fossils that are “characteristically abundant” in a particular strata worldwide. These fossils are usually marine invertebrates believed to have evolved into a more complex animal, or to have become extinct in a short period of time, but are found just about everywhere on planet earth. They are almost too common, being found virtually everywhere, from mountain tops to sea level and probably under the oceans, and are used to help identify the geological date of all new fossil finds. Now for the tricky part, how were these index fossils dated? By the fossils found in the same strata, of course!!! Index fossils are always used to date new fossils and new fossils were originally used to date the index fossils, based on when anthropologists believed they should have lived. Hmmmmmm.

Now, no competent scientist would risk their good name on this kind of circular reasoning, right? There must be an independent way to verify the conclusions of the index fossils, right? Breathe easy, there is. It is called radiometric dating, and that is where the igneous rock comes in. There are actually about half a dozen different methods of radiometric dating methods. The most common are the lead/uranium, potassium/argon, and rubidium/strontium methods. These are all based on the decay of a parent element into a daughter compound, by simply measuring the amount of the daughter compound and factoring in the known half lives of the parent element, we have a pretty good idea of the age of the rock (igneous rock always have some radioactive isotopes in them). We can even double check our dates, by using one or more of the other radiometric methods.

But as good scientists, we realize that for these methods to be accurate we certainly must be able to measure the present amount of the parent/daughter compound, but we also have to know the decay rate, and we must accurately know the beginning ratio of the parent/daughter compound. In other words, it needs to be a closed system. But do we know these things?

In almost all cases we have the technology to accurately measure both the parent and daughter compounds present in igneous rock today. However, science is sharply divided over what is the actual half life of many of these elements.

The beta-decay of Rubidium 87 into Strontium 87 is believed to have a half life of 47 billion years to 120 billion years, depending on who you listen to. Because of the disagreement over the true length of the half life, this method of age dating is usually calibrated by the Uranium/Lead method, so let’s have a look at that. We know that Uranium 238 decays into Lead 206 plus 8 Helium atoms, and we believe that it has a half life of about 4.5 billion years, plus or minus several hundred thousand years. Uranium 235 decays into Lead 207 plus 7 Helium atoms with a half life of about 700 million years, and Thorium 232 decays into Lead 208 plus 7 Helium atoms with a half life of 14.1 billion years. So this should be pretty easy to find out how far we are along the decay process by simply looking at these things.

Unfortunately, Uranium elements exist only in open systems, that is to say that many of the intermediate elements produced during this decay (Radon gas, Radium, Lead 210, etc) are free to move in and out of the system. Uranium itself is easily leachable by ground water, Radon gas passes freely in and out of porous rock, and lead migrates in and out of shale’s and other rocks, and can be easily manipulated by changes in temperature. But even more important is a phenomenon known as “free neutron capture” in which Lead 206 “captures” free neutrons in the environment and changes into Lead 207, which in turn captures more neutrons and changes into Lead 208. As more than half of all observed lead is 208, we have no way to know how much decayed from Lead 206 and 207 and how much simply “grabbed” any available free neutrons to become Lead 208. We are also aware that change to the earth’s magnetic field and other environmental changes seriously affect the decay rate.

Looking at Potassium/Argon dating is an even larger can of worms. The decay rate or “branching ratio” is unknown by a factor of 50%, meaning that the apparent ages need to be corrected to a control group. You guessed it. The control group is Uranium/Lead. Additionally, Argon is a gas, and as such, is very easily leachable in and out of the Potassium system. And so it goes. Radiometric dating is far from reliable, and in the end is always tempered with the use of the index fossils. In fact there is no radiometric dating lab on Earth that will accept a sample for dating without an index fossil. The sample is dated radiometrically, tempered mathematically, and corrected using the age of the index fossil. The age of the index fossil provide from a chart used by both the dating labs and the researchers in the field. Need a particular date, bring in the index fossil that corresponds to that date, and I might add the field researcher is not being dishonest, there are almost always several index fossils available at each site, they only need find the one that best represents what they believe to be true.

One way to accurately gauge the reliability of radiometric dating would be to date material using several methods and find some sort of a pattern. The Apollo 11 and 16 missions to the moon brought back many lunar rock samples. These have been radiometric dated using five different methods, revealing ages of several hundred million to over 18 billion!! Repeated tests on the same rocks with the same methods have not been able to agree on any kind of date. Why ? No index fossil from the moon, of course. Another way to test the reliability of these methods would be to test material of a known age. Tests of still warm lava from the Kilauea volcano have provided ages of 22 million years. Rocks formed in 1801 near Haulalei, Hawaii were measured by several different methods to be 160 million to 3 billion years old!!!

Lest we get too far into the weeds on this, remember that all measurements require as a part of the math, to know the percentage of parent material at the beginning. We assume 100% and all radiometric ages are derived from that assumption. But if the still warm volcanic rock measures 22 million years old we know that the parent amount was not 100%. If rocks known to be 180 years old measure 3 billion years perhaps some calibration of the instruments are in order. If the same rock measures from 200 million to 18 billion years depending on the isotope selected, this may not be the calculation you want to use to secure your eternity.

The Turbo Tax rule applies - garbage in, garbage out. Any sort of calculation made to attempt to find the actual age of something, requires that you know three things, the original state, the rate of change, and the present condition. Once those are established then we can start to consider environmental changes and all the other things that go along with this sort of calculation. Certainly in the area of radiometric dating we may only know one of these things. How then can a date be produced with a straight face? If, as a student, we preformed this kind of work, with this type of accuracy, we would not graduate. Not only would we not graduate, we would and should be, tossed out of school and asked never to reapply.