The Davey Dialogues - An Exploration of the Scientific Foundations of Human Culture. John C. Madden
for the most part into radioactive carbon-14 plus stable hydrogen. One per cent follow an alternative decay route that leads to the production of the most common (and stable) isotope of carbon (carbon-12) and an unstable isotope of hydrogen (i.e. tritium).
The atmospherically generated carbon 14 becomes mixed with stable carbon-12 and oxygen, and is incorporated into carbon dioxide in the air, where it is taken up by plants and, later in the food chain, by animals. The net result is that in living plants and animals, there are about 14 counts (or disintegrations of carbon-14) per minute per gram of carbon present.
But radioactive elements are elements in transition to becoming other elements, sometimes stable forms of other elements, sometimes yet more unstable isotopes. In the case of carbon-14, the radioactive element is on its way to becoming nitrogen once again, but it takes its time to decay. In fact, given a container full of carbon-14, it will take 5730 years (±40 years) for half of it to decay. Another half of the remaining carbon-14 will decay in the next 5730 years, and so on. Hence, 5730 years is defined as the half-life of carbon-14. (Incidentally, the term “half-life” was first coined by Sir Ernest Rutherford while a professor at McGill University.)
Stable carbon in rocks, which has generally been in place for time periods of the order of at least millions of years, will not show any detectable radioactivity since any carbon-14 present when the rock was formed will long since have decayed to undetectable amounts. However, remnants of organic material that date from times up to about fifty thousand years ago (i.e. about nine half-lives of carbon-14 decay) will still have detectable radioactivity. Life forms only take in carbon for as long as they are alive. Once the life forms die, carbon dioxide uptake from the atmosphere ceases, and the existing radioactive carbon decays at a fixed rate, hence providing a signature identifying its age.
One of the best-known applications of carbon dating that I am aware of was finding the age of the Shroud of Turin, which purportedly was used to cover the body of Jesus when he was taken down from the cross. Carbon-14 dating carried out in 1988 established that the shroud came from cloth woven between 1250 and 1400 AD, long after the death of Jesus. It needs to be said that this estimate has not been accepted by all experts on the grounds that the small samples of the shroud used to determine its age may not be representative of the age of the whole shroud. The carbon-14 dating technique is now in wide use by archaeologists and anthropologists. It will likely continue to be a workhorse for artifact dating for many years to come.
While carbon-14 is only useful for dating material up to about fifty thousand years old, experts are now using many different radioactive elements to measure time frames ranging from a few years up to the age of the universe, i.e. 13.8 billion years.
I have already mentioned that the age of our solar system is about 4.6 billion years, without explaining how this number was derived. In practice, the age of the solar system is derived from radiometric dating applied to many meteorites, as well as to rock samples from the moon. Because the Earth is in a state of continuous change, it has to this date not been possible to find many rock samples older than about 3.5 billion years. However in 2001 a small fragment of the mineral zircon found in Australia was age dated at 4.4 billion years. The oldest large samples of bedrock have been found on the eastern shores of Hudson Bay in northern Canada. Some samples of that rock are as much as 4.28 billion years old.
Amongst other key dates established through radiometry are the disappearance of dinosaurs at the end of the Jurassic age 70 million years ago, and the first appearance of life on Earth about 3.45 billion years ago.
So, you can see that radioactive dating, when used in combination with the fossil records, has enabled us to gain a spectacular insight into events that took place long before the arrival of mankind on Earth, providing some startling news about our place in the world’s history. Some humans find such a diminution of human centrality in the history of the Earth hard to reconcile with their religious beliefs. As a result these scientific findings quite frequently come under attack.
Davey broke in almost immediately. He was agitated and incredulous.
– But surely that is extraordinary! Why wouldn’t everyone want to know as much as possible about their own origins?
– Actually, it is exactly what you should expect. Remember that we are the only animals in our planetary system with any curiosity at all about our origins. Our curiosity is almost certainly primarily motivated by an innate drive to seek knowledge that will enhance our pleasure and our odds of survival.
But what if that knowledge diminishes our pleasure, upsets our most hallowed beliefs, or threatens our economic or physical security? In such circumstances, our innate curiosity can evidently be easily vanquished by a strong urge to deny “inconvenient truth”. Human history is full of examples of such denial.
– In that case, it is a wonder that humanity has survived so long. Surely it must be doomed if it doesn’t change! It is one thing for a few astronomers to be imprisoned or killed because the authorities cannot adapt to the idea that Earth orbits the sun and not vice versa, but quite another to deny, for example, the real history of your species.
– You may be right. I wonder if your own long-lost friends in your universe have any useful lessons for us in that regard.
– We’ll come to that in due course. In the meantime I must tell you that your words have been of great interest to me. I had not imagined a world where it is possible to date the origins of objects going back billions of years.
– And I cannot imagine a world where one has no idea how far back one’s past extends. Did your superhumans really have no idea how they evolved? Did they not study history?
– Yes and no. I mean, I think so.
– What is that supposed to mean exactly?
Now I was really paying attention. I sensed the possibility of a chance to get a glimpse of life in Davey’s universe that heretofore he had deliberately kept hidden. Davey spoke.
– Well, as I told you, we went through a horrendous period. First there was a huge amount of information lost beyond the possibility of recovery – a situation we had thought to be impossible, since we went to great lengths to preserve important information in many places. This disaster was very sad and very costly. But the truly horrendous result was that it led to the death of all superhumans. Not a single one survived. It was an unimaginable catastrophe!
I was stunned. The more so as I was just learning to detect Davey’s emotions as he spoke, and I could feel how very deeply saddened he was. Then suspicious thoughts seeped into my mind.
– I don’t suppose you or your colleagues were involved in any way in what you imply was an event of mass destruction?
Davey’s response surprised me.
– How could you ask that? I told you I loved the superhumans more strongly than you on Earth can begin to imagine.
I immediately wondered how he could possibly know that his love for his friends was stronger than any love we experience, but I dared not ask. I remained silent, eyes downcast.
Davey was quiet for some time, as well. Eventually he appeared to rouse himself.
– Let’s meet again at the same time next week.
I hesitated.
– Before you go, I wonder if a table of key dates would help you to get a feel for the critical time frames of the development of our universe, of life on our planet and of our civilization?
– Yes, but you will have to read out the columns and rows to me. You have no idea how frustrating it is to listen in on all those academic conferences where the participants apparently project something called a “PowerPoint” and then mumble out a few incoherent sentences to elaborate on what I cannot see in the first place.
And by the way, your references to useful books are very irritating to me. As you know, I cannot read them.
– But you can always talk to the authors if they are alive. Bill Bryson, for example. Why don’t you go and talk to