Her question was:
i still wonder how they start with any of the numbers they seem to date things with. don't you have to start with the very beginning of when it started out with to come up with the right number of years? like when you are born you are this many days, months, or years old from this time. i would like that explained to me. (so i can understand please.)I will be happy to oblige, Mom.
A. A Brief History of Earth-Aging Techniques.
Before the discovery of naturally occurring radiation (hell, before the discovery of radiation period!) it was generally assumed that the age of the Earth could be best determined by men who had been around since as long as we (collectively) could remember. Thus, the bible and other "ancient" (relatively speaking) books which recorded who begat who and when was seen as a "complete" picture for as to when and how the Earth came to be--after all, people lacked the proper knowledge and information to make an educated guess, and therefore "theories" defaulted to what we did know (i.e., the "god" theory) which inevitable placed the Earth, no matter how you did the math, at a few thousand years old. Not only did this view of Earth-Age default to "creationism," but it also defaulted to mankind being the only reliable "gauge," or constant if you will, to the keeping of time.
There's a reason we call this period of time "the Dark Ages," when man thought he was the end-all be-all of life on Earth (which, in case you were wondering, we are not). We didn't know Jack Shit (or his also-popular cousin Jack Squat) about anything mainly because we took the creationist approach to everything in life as opposed to the scientific approach, which can be summed up as such:
Creationist Approach to Science: Take a preconceived idea, then look for any available data (whether within context or not) to back that "theory" (i.e., preconceived notion) into looking like something resembling a good idea.This is the method that has illuminated the world, nay, the universe, into the amazing place in which we find ourselves: living longer, healthier, better.
Scientific Approach to Science: Ask a question, and then try everything within your power to prove that notion wrong in any way, shape, or form that you can think of. If the idea withstands every single attempt you can think of (and then that everyone else can think of using honest, testable methods), then what you have is a working theory which will be assumed true until otherwise honestly, retestably disproven.
B. How Science Knows the Age of the Earth (Give or Take a Few Years):
It's actually very simple. You take a certain atom, find out how long it has been decaying, and "Walla!", you know that creationists are nothing if not full of hot air. In layman's terms, the reason we know that the Earth is about 4.60 ± 0.07 billion years old is due to the fact that certain atoms decay at very stable, very measurable rates, and thus depending on how decayed those isotopes are, that's how old the isotope is, and thus the age of the item from which the isotope has been removed. (Granted, this is very simplified, but you get the idea.)
In technical terms:
Radiometric dating is based on the decay of long-lived radioactive isotopes that occur naturally in rocks and minerals. These parent isotopes decay to stable daughter isotopes at rates that can be measured experimentally and are effectively constant over time regardless of physical or chemical conditions. There are a number of long-lived radioactive isotopes used in radiometric dating, and a variety of ways they are used to determine the ages of rocks, minerals, and organic materials. Some of the isotopic parents, end-product daughters, and half-lives involved are listed in Table 1. Sometimes these decay schemes are used individually to determine an age (e.g., Rb-Sr) and sometimes in combinations (e.g., U-Th-Pb). Each of the various decay schemes and dating methods has unique characteristics that make it applicable to particular geologic situations. For example, a method based on a parent isotope with a very long half-life, such as 147Sm, is not very useful for measuring the age of a rock only a few million years old because insufficient amounts of the daughter isotope accumulate in this short time. Likewise, the 14C method can only be used to determine the ages of certain types of young organic material and is useless on old granites. Some methods work only on closed systems, whereas others work on open systems.1 The point is that not all methods are applicable to all rocks of all ages. One of the primary functions of the dating specialist (sometimes called a geochronologist) is to select the applicable method for the particular problem to be solved, and to design the experiment in such a way that there will be checks on the reliability of the results. Some of the methods have internal checks, so that the data themselves provide good evidence of reliability or lack thereof. Commonly, a radiometric age is checked by other evidence, such as the relative order of rock units as observed in the field, age measurements based on other decay schemes, or ages on several samples from the same rock unit. The main point is that the ages of rock formations are rarely based on a single, isolated age measurement. On the contrary, radiometric ages are verified whenever possible and practical, and are evaluated by considering other relevant data. (Source.)This article is a tough read if you aren't used to engaging your neurons in heavy reading, but if you are able to, it's well worth the read!
Another way we can gauge the age of the universe is through light. (You know, that thing supposedly created and separated from darkness on Day One?) Light travels at a certain speed in the vacuum of space--never faster, never slower. It is constant at exactly 299,792,458 m/s (meters per second). Thus, when we look at a star (let's say, for shits and giggles, Alpha Centauri): we know that it is 4.22 light years away (i.e., it took 4.22 years for the light originating on that star to reach our eye balls...) But there are stars we see that have taken millions of years for their light to cross the cosmos, some as much as 500 million light years away! Thus that star, this universe, has been around for at least that long!
Of course, the standard "creationist" answer to this "issue" is that god, when he created the stars, created the "light beams" from those stars already in place--that is, even though "light" was somehow created on Day One, and "stars" were created on Day Four (even though somehow the sun doesn't make "star status," being called "the greater light"...), that is "proof" that the universe couldn't possibly be older than 6,000 to 10,000 years--the light was "already there." In other words, the light being seen never came from the star itself, but somehow "appeared" midway so that people would see the star long before its light ever got here. This would be a lot like California raisins coming from California to Pennsylvania in just under 2 hours: The raisins aren't really from California because they (and the horse they rode in on) popped into existence a mere two hours away--thus, not California raisins, but "midway" raisins deceptively created to seem like California raisins... Or if I were traveling to Pennsylvania from California--did I actually exist if I were created "midway" and made it to PA in two hours? Was I actually ever coming from California? The answer would be a patent "No!" It would only seem as if I had traveled from California, when in fact I did no such thing...
The only huge issue with this "theory" (disregarding the plethora of smaller ones...) is that, when we see stars exploding, or meteors and comets collapsing into black holes, did they actually happen? Or were those light beams also created midway, and to what purpose? It would seem a great big lie, a deception, if you will, on the part of the supposed creator! These events are fallacies of what "would have happened" if the universe were millions of years old... Do you see the problem? God creates a light show that never happened, but which he knew would "seem" millions of years old?
If one is going to believe, and take on "faith," that the bible is the perfect revelation of god, but that the light (and it's constant speed) is contradicting this, how can one trust any physical evidence at all? And if the physical evidence is deceptive, and cannot be trusted as reliable, what is a person to make of his "perfect word", his "written revelation"? How do they even know that the last five minutes happened?! It all could have been created "midway"!!! Jesus might never have died! Adam most likely never sinned!! Where is the "cut-off" for deceptive "midway" creations?
If these fake star deaths, comet collisions, and black hole-forming light shows never happened, how do we know that anything we perceive is true? Once we credit the "god theory" with "midway light" from stars, we credit god with a whole host of deceptive physical things which cannot be held true--in fact, any and all data is at best deceptive, at worst patently false... God would be deceiving us in everything we see, taste, hear, feel, or smell...
If one cannot reconcile the deceitfulness of god (or at the very least, the deceitfulness of his creation) with the biblical belief that god is "good" and non-deceitful, then we must conclude that the light has, in fact, been traveling for millions of years...
So, there you have it: the reason we know that the Earth is as old as science says it is. So for those of you who didn't know, I hope you got an education; for those of you who did know, I hope this was an adequate (albeit short and sweet) refresher course, and for those of you who stick your heads in the sand and call it "faith," well here's hoping that while your head is in the sand, you take the time to measure it's age radiometrically and learn a thing or two...
Time allowing, by this Saturday: A Moral Defense of Evolution. (Trust me, it's not only possible, but factual...)