Volcanism

In a recent conversation with a close friend from Grad school, the issue of earth’s true age came up. Why, you ask? For those who know me, I was raised Catholic (Confirmed, even), but have faced many conflicts with the church I grew up in, and follow more academic schools of thought when it comes to the question of “how we got here.” For years, Christianity’s firm stance on Creation and a six-day turn around didn’t suffice as answers. As I entered college and studied anthropology and earth sciences, I finally felt complete, spiritually speaking.

Weird, isn’t it?

This brings us back to the issue my friend and I were once again hashing out: science versus religion. I told him that years ago during a family trip, a cousin of mine picked up a rock as we wandered around the Smoky Mountains at the Tennessee/North Carolina border and boldly said the rock was only a couple thousand years old, and that earth was not much older. Of course, I knew he was full of it. After telling my friend about this encounter, we tried to figure out why so many people did not believe the earth was more than 6,000 years old. Hadn’t anyone taken a general science class? At least heard of the geologic time scale?

In many cases, no.

Which leads me to today’s post on radiometric, or radioactive dating as a means of figuring out not only the age of the earth, but piecing it together into distinct periods. But before I move forward, I want to make it very clear that I am  not trying to convince anyone to change their beliefs, or what they believe is incorrect. As I said in my first post, I’m merely sharing what I believe is the best answer for me. I have a lot of respect for religion, I believe it serves the purpose for which a person needs it; it just isn’t for me.

Before I talk about radiometric dating, I want to talk first about the 6,000 year figure mentioned before. How did the Church come to that number? I’ll tell you, my dear readers. According to various ministries, the earth is aged between 6,000 and 10,000 years old. In the 17th century, Bishop James Ussher of the Church of Ireland determined the date of earth’s creation to be October 23, 4004 B.C. Ussher apparently used genealogies described in Genesis to back-track through earth’s history. Naturally, there are several issues with this method: a) the Bible is famous for “telescoping” or paraphrasing genealogies for brevity; b) Ussher assumed a couple of things, that the calendar days were the same in the Bible as they were in the 17th century, and that each member of each generation conveniently died the day before his birthday, so that each generation was exactly 40 years. This brings me to the third problem, c) translations for “father” “son” and “grandfather” would have differed from one translation to the next, thereby skewing the progression of one generation to the next. Lastly, God made a covenant to last 1,000 generations of man; assuming each generation to be 40 years, that would mean earth had to be at least 40,000 years. I know I’m not a math major, but that’s more than 6,000 years.

Creationists, not surprisingly, take enormous issue with radiometric and index dating, often citing fallacies and gaps in scientists’ logic, claiming the whole field of study is based on the educational guess of others. I won’t go into too much detail of their entire platform, but I’m just putting it out there that the Creation front is strongly against the theory and practice of radiometric dating.

So what exactly is radiometric decay? This is the process of an unstable isotope becoming a stable isotope. An isotope is a chemical element with unstable neutrons. Atoms typically have an equal number of protons and neutrons; too many or too few makes the atom unstable. The shedding of particles to rebalance the isotope leads to a new isotope, or daughter isotope. If a sample has more parent/ isotopes, the younger it is; if there are more daughter/stable isotopes, the older the sample is, as more time has passed for the parent atom to shed unstable particles and create daughter isotopes. You may have heard of Carbon-14, one of the most widely used isotopes for measuring the age of anything younger than 50,000 years old. This isotope is formed in our atmosphere by the bombardment of nitrogen-14 with the sun’s rays. Every living organism contains Carbon-14. There are, however, extreme limitations to using Carbon-14. First of all, its half-life is simply insufficient to dating anything above the 50,000 year threshold, which means it could not accurately measure the age of earth. What Carbon-14 is, though, is one of many isotopes used in dating anything from petrified wood, fossils, and rocks and rock formations.

What’s the point of all this, you may ask? The point is many isotopes have half lives that range from millions to billions of years. Commonly used isotopes are Uranium-238 (with a half life of 4.5 billion years), Uranium-235 (with a half life of 704 million years), and Potassium-40 (with a half life of 1.25 billion years). The biggest issue with these isotopes is that they do not exist in sedimentary rock, where fossils are found, but in igneous rock. Fossils, naturally, are not found in igneous rock, simply because they would be incinerated on contact. It is extremely useful, however, when determining the age of fossils and rock layers to complete the geologic time scale, shown below.

When magma (where igneous rocks come from) cools and crystallizes, new minerals often contain chemical elements, some of which are radioactive isotopes like the ones listed above. How, then, does this help in not only determining the age of certain fossils or rock layers, but the age of earth? Scientists often use layers of igneous rock as “brackets” for the sedimentary layers containing fossils. And one method alone is never used. Several isotopes and many different tests are run before a number is determined.

With these basic principles set, now, we can begin to understand the tools used to determine how old earth and our galaxy is. Because active plate tectonics regularly destroy the upper layers of the crust, crystals found from deeper layers beneath the crust are used to determine age. Zircon crystals, the hardest rocks on earth, have surfaced and been dated at 4.3 billion years. Moon rocks have also been huge in determining the age of the earth, as it was formed around the same time. Some moon rocks found have been dated as old as 4.5 billion years.

In short, because of science, most people can comfortably say the earth is considerably older that 6,000 or even 10,000 years. And, once again, geology helps give us the answers. Just when you thought rocks were boring, think again. And, as always, go out and seek adventure and answers (or maybe you only find more questions, but that’s okay, too).