How, exactly, is dating done?

The methods vary depending on the isotopes, but in general you compare the father and daughter isotopic ratio. However, it's more than that. For example, in isochron dating methods, you also compare the ratio of a different isotope of either the parent or daughter that normally exists in nature at a fixed ratio to the radioisotope; this helps you confirm whether what you've determined as the amount of the parent that has decayed to daughter is correct. Also, on controversial dates, multiple methods are generally used whenever possible.Certain types of dates have a number of constraints as to when and where they can be used to obtain valid data (something that creationists often abuse). For example, carbon dating is not to be used in the following situations:- When dating marine fossils, or species that consume a lot of marine organisms. The oceans recycle a lot of deep, old carbon.
- When dating fossils in highly volcanic areas. Volcanos recycle a lot of old carbon.
- Not for use with for fossils that have been taking in carbon since the 1950s (nuclear testing has thrown off ratios) without a high margin of error.
- Like all dating methods, not with fossils that are beyond the acceptable error range for a given method (carbon dating is for relatively "young" fossils only, while your uranium dating methods are only for relatively "old" fossils, as an example).Due to the unusual nature of carbon dating, it is one of the few methods that has to be calibrated (it is typically calibrated with tree ring chronology). However, calibration factors, to the best of my knowledge, are all under 20% for dates before the 1950s. Other methods of dating typically use no calibration factor.Again, what equipment you use depends on what dating method you use; here's how carbon dating is done - as step by step guide, with pictures.------------------
"Illuminant light,
illuminate me."[This message has been edited by Rei, 11-17-2003]

quote:

---

I always thought multiple methods was the isochron. Is there a difference?

---

Not exactly. (Edit: JonF described this in a lot of detail, so I'll save your time).

quote:

---

Does the HCl acid mess with the parent-daughter isotope ratio? Might that be kind of risky?

---

No. Hydrochloric acid contains two elements: hydrogen, and chlorine. It does not contain carbon (at least not a statistically significant amount at the purities they use in carbon dating). Acid cannot change isotopic ratios, which are determined at the atomic level, not the molecular level. If chemical reactions could readily cause nuclear decay, the atomic bomb would have been a lot easier to build. Chemical reactions don't mess with the nucleus.

quote:

---

How do we know how much of the parent isotope/daughter isotope was present to start with? YEC's are telling me that we estimate. Please don't tell me they're right.

---

As I mentioned concerning carbon dating (which is different from most methods), there is the assumption of the same C12/C14 ratio in the atmosphere as there was before the atomic bomb tests, with a calibration factor. The calibration factor is always less than 20% for dates before the 1950s, and is usually just a few percent - consequently, this cannot be used as an excuse for making a young earth look old. These calibration factors are largely determined by dendrochronology - i.e., checking carbon ratios in tree rings. While individual trees don't live that long, tree rings are effected by environmental factors - drought, flood, fire, etc. The areas of damage can be lined up in multiple trees in a given region. Bristlecone chronologies, for example, go back 9,000 years (and they're working on extending it). They don't just use a single line of trees; they do a statistical analysis on all of the trees that they can examine, to ensure that no matter how you line up the rings, significant events always match up. Before then, we have to rely on other methods (such as ice cores, which have annual lines) to attempt to determine the calibration factor - but again, it's always rather small factor. Ice cores correspond to dendrochronology, over the period of time that we have tree ring data.How do we know what the original ratios were? Well, it depends on the method; different methods have additional methods to confirm what original ratios were. However, all of them have the same thing: They correspond to each other amazingly well. Even on cases where it is expected to have a strong degree of difficulty (such as dating from rubble piles), it's rare to get more than a 10% error between different methods. In most cases, a 1% error is about all you'll get. Isochron dating adds another correlation. This cross-correlation between entirely different methods ensures confidence in them. Furthermore, there's another issue that all share in common: geographical correlation. You can date a trilobite fossil from anywhere in the world, anywhere you like. It doesn't matter what sort of sediments it was preserved in - you'll never find a single trilobite fossil that dates more recently than the upper permian, within a small margin of error, as an example. Not just the fossil, but you can date the *rocks* that surround the trilobite (in case one thinks that the fossil itself is storing minerals strangely), anywhere in the same layer, and get the same date.To get a young earth, you not only need to show that the daughter product was mostly in the rock to begin with, and that the parent wasn't, but you need to show why the ratios of *several different* minerals, all with different ratios of parent to daughter, come up with being just the precise amount decayed to present the same age.One theory that creationists have proposed is rapid decay - that for some God-given reason, radioactive decay went faster in the past, and then reached a steady slow state today which doesn't change. This is, of course, nonsense. Radioactive decay is what heats the earth. Just the amount of decay that would have had to occur in surface granites to reach our current matching ratios would have ensured that the surface of the planet was a molten slag to this day.It's good to see someone being inquisitive - I'm glad to have you here. ------------------
"Illuminant light,
illuminate me."[This message has been edited by Rei, 11-17-2003]

quote:

---

The other change does mention the conditions --- I don't remember the exact numbers -- something like 200 million degress if I remember right. That fact that this might apply to a supernova and not even the core of the sun seems to have gotten left out. Something of an oversight perhaps?

---

You know, I bet if you took the atoms, ripped off all their electrons but kept them tightly contained in a penning trap, cooled them to near becoming a bose-einstein condensate (so that they won't move around to much), and then fired an intense barrage of high energy radiation at them, you could probably increase their half lives that way, too. Or perhaps if you took them and put them in a particle accelerator, ramped them up to a few TeV's, and collided them with a wall.... See? There's lots of ways that you could cause the atoms to break down faster!... so that they can release their energy faster, and give the Earth's crust a nice meltdown.... ------------------
"Illuminant light,
illuminate me."[This message has been edited by Rei, 11-17-2003]

Here's an excellent page on radiometric dating. It covers pseudo-isochrons.The Skeptic Files - SkepticFiles Setting------------------
"Illuminant light,
illuminate me."