Originally posted by Jan Ardena
You obviously do not know, so just tell me anyway.
If you can't, i will understand, but i would like to know either way.
As you wish. The following explains how I know the age of Earth is 4.5 billion years old. Hope you can read through all of them. If you think it's too long, you can try to read the bold face subtitle that interests you the most.
1. Rocks
Rocks are made up of many individual crystals, and each crystal is usually made up of at least several different chemical elements such as iron, magnesium, silicon, etc. Most elements in nature are stable and do not change. However, some elements are not completely stable in their natural state. Some atoms eventually change from one element to another by a process called radioactive decay. If there are many atoms of the original element, called the parent element, the atoms decay to another element, called the daughter element, at a predictable rate. The passage of time can be charted by the reduction in the number of parent atoms, and the increase in the number of daughter atoms.
2. Radiometric dating
Radiometric dating can be compared to an hourglass. When the glass is turned over, sand runs from the top to the bottom. You cannot predict exactly when any one particular grain will get to the bottom, but you can predict from one time to the next how long the whole pile of sand takes to fall. Once all of the sand has fallen out of the top, the hourglass will no longer keep time unless it is turned over again. Similarly, when all the atoms of the radioactive element are gone, the rock will no longer keep time (unless it receives a new batch of radioactive atoms).
Unlike the hourglass, where the amount of sand falling is constant right up until the end, the number of decays from a fixed number of radioactive atoms decreases as there are fewer atoms left to decay. If it takes a certain length of time for half of the atoms to decay, it will take the same amount of time for half of the remaining atoms, or one-fourth of the original total, to decay. In the next interval, with only one-fourth remaining, only one eighth of the original total will decay. By the time ten of these intervals, or half-lives, have passed, less than one thousandth of the original number of radioactive atoms is left. Also unlike the hourglass, there is no way to change the rate at which radioactive atoms decay on earth. If you shake the hourglass, twirl it, or put it in a rapidly accelerating vehicle, the time it takes the sand to fall will change. But the radioactive atoms used in dating techniques have been subjected to heat, cold, pressure, vacuum, acceleration, and strong chemical reactions without any significant change in their decay rate.
3. Radiometric clocks
There are now well over forty different radiometric dating techniques, each based on a different radioactive isotope.
Radioactive Isotope : half life in years
Samarium - 147 : 106 billion
Rubidium-87 : 48.8 billion
Rhenium-187 : 42 billion
Lutetium-176 : 38 billion
Thorium-232 : 14 billion
Uranium-238 : 4.5 billion
Potassium-40 : 1.26 billion
Uranium-235 : 0.7 billion
Beryllium-10 : 1.52 million
Chlorine-36 : 300000
Carbon-14 : 5715
Notice the large range in the half-lives. Isotopes with long half-lives decay very slowly, and so are useful for dating correspondingly ancient events. Isotopes with shorter half-lives cannot date very ancient events because all of the atoms of the parent isotope would have already decayed away, like an hourglass left sitting with all the sand at the bottom. Isotopes with relatively short half-lives are useful for dating correspondingly shorter intervals, and can usually do so with greater accuracy, just as you would use a stopwatch rather than a grandfather clock to time a 100-meter dash. On the other hand, you would use a calendar, not a clock, to record time intervals of several weeks or more.
4. Half-lives
The half-lives have all been measured directly, either by using a radiation detector to count the number of atoms decaying in a given amount of time from a known amount of the parent material, or by measuring the ratio of daughter to parent atoms in a sample that originally consisted completely of parent atoms. Work on radiometric dating first started shortly after the turn of the century, but progress was relatively slow before the late forties. For many of the dating techniques, we now have had fifty years over which to measure and remeasure the half-lives. Very precise counting of the decay events or the daughter atoms can be done, so that while the number of, for example, rhenium-187 atoms decaying in 50 years is a very small fraction of the total, the resulting osmium-187 atoms can be very precisely counted.
The uncertainties on the half-lives given in the table are all very small. All the half-lives are known to better than plus/minus about two percent except for rhenium (5%), lutetium (3%), and beryllium (3%). There is no evidence of any of the half-lives changing over time, and such a thing is forbidden by the laws of physics.
5. Age of Earth
We now turn our attention to what the dating systems tell us about the age of the earth. The most obvious constraint is the age of the oldest rocks. These have been dated at up to about four billion years. But actually only a very small portion of the earth's rocks are that old. From satellite data we know that the earth's surface is constantly rearranging itself little by little as earthquakes occur. Such rearranging cannot occur without some of the earth's surface disappearing under other parts of the earth's surface, remelting some of the rock. So it appears that none of the rocks have survived from the creation of the earth without undergoing remelting, metamorphism, or erosion, and all we can say--from this line of evidence--is that the earth appears to be at least as old as the four billion-year-old rocks.
When scientists began systematically dating meteorites, they learned a very interesting thing: nearly all of the meteorites had practically identical ages, at 4.56 billion years. These meteorites are chips off the asteroids. When the asteroids were formed in space, they cooled relatively quickly (some of them may never have gotten very warm), so all of their rocks were formed within a few million years. The asteroids' rocks have not been remelted ever since, so the ages have generally not been disturbed. Meteorites which show evidence of being from the largest asteroids have slightly younger ages. The moon is larger than the largest asteroid. The oldest rocks we have from the moon do not exceed 4.1 billion years, though a larger sampling might yield some slightly older ages. Most scientists think that all the bodies in the solar system were created about the same time. There is evidence from the uranium, thorium, and lead isotopes that links the earth's age with that of the meteorites. This would make the earth about 4.5-4.6 billion years old.
Notice one other important detail about radioactive isotopes. Most of the naturally-occurring radioactive isotopes mentioned above have very long half-lives, on the order of billions of years. The only ones with shorter half-lives are those which have a source constantly replenishing them, such as the carbon-14, beryllium-10 and chlorine-36 produced by cosmic rays. We can make hundreds of other radioactive isotopes with half-lives shorter than a billion years, but they do not occur naturally on earth. Occasionally there is evidence that these isotopes existed at some point in the past, but have since decayed completely away. The longest half-lives of this group of "extinct" radionuclides are close to a hundred million years. Why do we find almost no short-lived radionuclides and so many long-lived ones? This is what one would expect to find if God had created the earth approximately four and a half billion years ago. The earth is old enough that radioactive isotopes with half-lives of up to a hundred million years decayed away, but not so old that radioactive isotopes with half-lives close to a billion years are gone.
6: Oldest rocks
Some of the oldest rocks on earth are found in Western Greenland. Because of their great age, they have been especially well studied. The table below gives the ages, in billions of years, from twelve different studies using five different techniques on one particular rock formation in Western Greenland, the Amitsoq gneisses.
Technique : Age Range (billion years)
uranium-lead : 3.60¡À0.05
lead-lead : 3.56¡À0.10
lead-lead : 3.74¡À0.12
lead-lead : 3.62¡À0.13
rubidium-strontium : 3.64¡À0.06
rubidium-strontium : 3.62¡À0.14
rubidium-strontium : 3.67¡À0.09
rubidium-strontium : 3.66¡À0.10
rubidium-strontium : 3.61¡À0.22
rubidium-strontium : 3.56¡À0.14
lutetium-hafnium : 3.55¡À0.22
samarium-neodymium : 3.56¡À0.20
Note that scientists give their results with a stated uncertainty. They take into account all the possible errors and give a range within which they are 95% sure that the actual value lies. The top number, 3.60¡À0.05, refers to the range from 3.55 to 3.65 billion years. The size of this range is every bit as important as the actual number. One number with a small uncertainty range is more accurate than a number with a larger range. For the numbers given above, one can see that all of the ranges overlap and agree between 3.62 and 3.65 billion years as the age of the rock. Several studies also showed that, because of the great ages of these rocks, they have been through several mild metamorphic heating events that disturbed the ages given by potassium-bearing minerals.
7. Can we trust the dating system
Some Christians question whether we can believe something so far back in the past. My answer is that it is similar to believing in other things of the past. It only differs in degree. Why do you believe Abraham Lincoln ever lived? Because it would take an extremely elaborate scheme to make up his existence, including forgeries, fake photos, and many other things, and besides, there is no good reason to simply have made him up. Well, the situation is very similar for the dating of rocks, only we have rock records rather than historical records. Consider the following:
There are well over forty different radiometric dating methods, and scores of other methods such as tree rings or ice cores.
All of the different dating methods agree--they agree a great majority of the time over millions of years. Some Christians make it sound like there is much disagreement, but this is not so. The disagreement in values needed to support the position of young-earth creationists would require differences measured by orders of magnitude (e.g., factors of 1000, 10,000, a million, or more). The differences actually found in the scientific literature are usually close to the margin of error, not orders of magnitude.
There are vast amounts of data overwhelmingly favoring the old earth model. There are several hundred laboratories around the world actively doing radiometric dating; all but possibly one or two favor the old earth. A quick word search of the word "dating" shows that among the Caltech library holdings, in 1994 alone there were at least 450 research papers published specifically on dating of geologic and archaeologic materials. At least 95 of these were on rubidium-strontium, and 42 were on potassium-argon or argon-argon. Essentially all these favored an old earth.
Radioactive decay rates have been measured for over forty years now for many of the decay clocks without any observed changes. And it has been over eighty years since the uranium decay rate was first determined.
The mathematics for determining the ages from the observations is relatively simple.
The last two points deserve more attention. Some Christians have argued that something may be slowly changing with time so that all the ages look older than they really are. The only two quantities in the exponent of a decay rate equation are the half-life and the time. So for ages to appear longer than actual, all the half-lives would have to be changing in sync with each other. One could consider that time itself was changing if that happened (Remember that our clocks are now standardized to atomic clocks!). And such a thing would have to have occurred without our detection in the last 80 years, which is already 4% of the way back to the time of Christ.
It would not be inconsistent with the scientific evidence to conclude that God made everything relatively recently, but with the appearance of great age, just as Genesis 1 and 2 tell of God making Adam as a fully grown man (which implies the appearance of age). That is a philosophical and theological matter which we won't go into here, though it has some shades of the Abraham Lincoln example. We only note here that an apparent old earth is consistent with the great amount of scientific evidence.
8. Common Misconceptions Regarding Radiometric Dating Techniques
There are several misconceptions that seem especially prevalent among Christians. Most of these topics are covered in the above discussion, but they are reviewed briefly here for clarity.
1. Radiometric dating is based on index fossils.
This is not at all true, though it has actually been suggested. Radiometric dating is based on the half-lives of the radioactive isotopes. These half-lives have been measured over the last 40-80 years. They are not calibrated at all by fossils.
2. The decay rates are poorly known, so the dates are inaccurate.
Most of the decay rates used for dating rocks are known to within 2 percent. Uncertainties are only slightly higher on rhenium (5%), lutetium (3%), and beryllium (3%). Such small uncertainties are no reason to dismiss radiometric dating. Whether a rock is 100 million years or 102 million years old does not make a great deal of difference.
3. A small error in the half-lives leads to a very large error in the date.
Since exponents are used in the dating equations, it is possible for people to think this might be true, but it is not. If a half-life is off by 2%, it will only lead to a 2% error in the date.
4. Decay rates can be affected by the physical surroundings.
This is not true in dating rocks. Radioactive atoms used for dating have been subjected to heat, cold, pressure, vacuum, acceleration, and strong chemical reactions without any measurable change. The only exceptions, which are not relevant to dating rocks, are discussed under the section, "Doubters Still Try," above.
5. No one has measured the decay rates directly; we only know them from inference.
Decay rates have been directly measured over the last 50-80 years. In some cases a batch of the pure parent material is weighed and set aside for a long time, and then the resulting daughter material is weighed. In many cases it is easier to detect radioactive decays by the energy burst each decay gives off. For this, a batch of the pure parent material is carefully weighed and then put in front of a Geiger counter which counts the number of decays over a long time.
6. The decay rates might be slowing down over time, leading to incorrect old dates.
While we cannot rule out that this could possibly have happened in the past, there is no evidence that anything of the sort has happened in the past century. And the following argument makes this suggestion meaningless in terms of apparent ages: Since the different dating methods are in good agreement, all of the half-lives must have slowed down the same amount together. Such an occurrence would be the same as if time itself slowed down. But everything still appears very old, so why complicate things by making this suggestion in the first place?
7. There is little or no way to tell how much of the decay product was originally in the rock, leading to anomalously old ages.
A good part of this work is devoted to explaining how one can tell how much of a given element or isotope was originally present. Usually it involves using more than one sample from a given rock. By comparing the ratios of parent and daughter isotopes relative to a stable isotope for samples with different relative amounts of the parent isotope, one can determine how much of the daughter isotope would be present if there had been no parent isotope. This is the same as the initial amount (it would not change if there was no parent isotope to decay). Figure 4 and the accompanying explanation tell how this is done most of the time. While this is not absolutely 100% foolproof, comparison of several dating methods will always show whether the given date is reliable.
8. There are only a few different dating techniques.
We have listed eleven different radiometric dating techniques and discussed them. These make up only the tip of the iceberg. There are over forty different radiometric dating techniques in use, and there are many other dating techniques making use of rare stable isotopes, yearly variations such as tree rings and ice cores, and other reliable methods.
9. "Radiation halos" in rocks prove that the earth was young.
This refers to tiny halos of crystal damage surrounding spots where radioactive elements are concentrated in certain rocks. Halos thought to be from polonium, a short-lived element produced from the decay of uranium, have been found in some rocks. A plausible explanation for a halo from such a short-lived element is that these were not produced by an initial concentration of the radioactive element. Rather, as water seeped through cracks in the minerals, a chemical change caused newly-formed polonium to drop out of solution at a certain place and almost immediately decay there. A halo would build up over a long period, although the center of the halo never contained more than a few atoms of polonium at one time. "Hydrothermal" effects can act in ways that at first seem strange, such as the well-known fact that gold--a chemically unreactive metal with very low solubilities--is concentrated along quartz veins by the action of water over long periods of time. Other researchers have found halos produced by an indirect radioactive decay effect called hole diffusion, which is an electrical effect in a crystal. These results suggest that the halos in question are not from short-lived isotopes after all.
At any rate, halos from uranium inclusions are far more common. Because of uranium's long half-lives, these halos take at least several hundred million years to form. Because of this, most people agree that halos provide compelling evidence for a very old earth.
10. Only atheists and liberals are involved in radiometric dating.
The fact is that there are many Bible-believing Christians who are involved in radiometric dating, and who can see its validity firsthand. Most of the members of the Affiliation of Christian Geologists are firmly convinced that radiometric dating shows evidence that God created the earth billions, not thousands, of years ago.
11. Different dating techniques usually give conflicting results.
This is not true at all. The fact that dating techniques most often agree with each other is why scientists tend to trust them in the first place. Nearly every college and university library in the country has periodicals such as Science, Nature, and specific geology journals which give the results of dating studies. The public is usually welcome to (and should!) browse in these libraries. So the results are not hidden; people can go look at the results for themselves. In 1994 alone, at least 450 research articles were published, essentially all favoring a very old earth. Besides the scientific periodicals which carry up-to-date research reports, specific suggestions are given below of books for further reading.