Hot answers tagged

25

Yes, the age of the Earth is about 4.5 billion years (4,500 million years). Your linked articles describes well how it was formed and how we know about it. The uncertainty is less than 1% and depends partly on the radiometric dating methods and partly on the definitions. Sometimes the age is said to be 4.567 Ga, that might be a little too exact number to ...


13

While lead 206 does occur naturally, unless a zircon (a zirconium silicate crystal) is contaminated with lead or has been around a long time, it will contain no lead. Zirconium, uranium, and thorium have similar chemistries. Lead has a dramatically distinct chemistry. The chemical reactions that form zircons can accommodate uranium or thorium replacing ...


9

The oldest undisputed fossil are Stromatolites, bacterial mats, the oldest of which are dated ay 3.7 billion years ago. The key term here is undisputed, there are other possible fossils but it is very hard to have certainty with chemical or cellular fossils. The oldest uncertain fossils trace back to 4.28 billion years and are possible bacteria trapped in ...


9

The four stable isotopes of lead and their relative abundance on Earth are: 204Pb (1.4%), 206Pb (24.1%), 207Pb (22.1%) and 208Pb (52.4%). Lead-204 is a primordial nuclide and is not a radiogenic nuclide. 206Pb, 207Pb, and 208Pb form as part of the radioactive decay chains of Uranium and Thorium and they also occur as primordial nuclides that were made in ...


8

As noted in the comments the wikipedia articles (at the time this question was submitted) are contradictory. There are quite a few steps to the logic of how argon-argon dating works but none are too complicated, although I won't go into all of the possible interferences. One thing to keep in mind is that high-precision isotope measurements always measure ...


7

The short answer is no, because we always have some constraint of how old something is. Sometimes we have fossils with large date error bars, and often we do not know for how long that species existed. A large date range constraint in some cases, like archeology, might not be useful. If the specimen is taken without noting the location it was taken from, ...


7

A good chronometer is one that satisfies the following conditions: We know exactly how much it had of something when it began We know exactly the rate of the accumulation of the thing, and the rate is constant. For example, U-Pb dating in zircon is an excellent chronometer. We know exactly how much Pb is in zircon when it crystallises (= none) and we know ...


6

The cited paper, and ones like it, are young earth creationist nonsense. The Geoscience Research Institute is an arm of the Seventh Day Adventists, whose official position is that "in a recent six-day creation the Lord made “the heavens and the earth, the sea, and all that is in them” and rested on the seventh day." This is a central tenet of Seventh Day ...


5

1) D* (radiogenic isotope) and Dref (stable reference isotope) are two isotopes of the same element. P is the radioactive parent of D*, and is a different element. Chemical fractionation between P and Dref occurs as the rock solidifies because different elements are preferentially incorporated in different minerals depending on how well their ionic radii and ...


4

It does seem like it's impossible to know unless you have additional information. However, I think there is a hint in there. See this white halo around the intrusion? My guess (and I could be wrong here) is that it's not there for artistic reasons but rather it's there to provide a very strong hint. My feeling that this is some kind of metamorphosed contact ...


4

First of all, you shouldn't take creationists seriously; like flat earthists, their views are totally out of touch with reality. Rates of radioactive decay have been tested many times in the laboratory and found to be accurate. However, there have been some instances where a substantial change of temperature or the formation of a chemical compound involving ...


4

I run an argon lab which does also K-Ar measurements. The sample amount depends on the age because you need enough signal strength to measure the radiogenic argon component precisely. Young rocks have very low 40Ar* and to get enough volts on the detector you need more sample. Having the incorrect amount is akin to trying to measure micrometers with a ...


4

There are other, mostly chemical processes which alter the isotope ratios. Isotope dating uses a combination of them. This is why it can not be used always, for any radioactive isotopes, only in special circumstances. It also requires very sensitive measurements (below in the second example, close to induvidually count lead atoms in microscopic zircon ...


4

Fossils are only in very rare cases dated directly, because they do not contain sufficient radioactive isotopes for dating. Most geological periods are first and foremost defined by biostratigraphy- fossil assemblages, typically. The Cambrian period starts with the Fortunian stage - this stage is defined by the appearance of a certain trace fossil in ...


3

Weren't all the natural radioactive isotopes created during the formation of the solar system? The half life of carbon 14 is 5730 years, orders of magnitude less than the age of the solar system. Carbon 14 is constantly being created in the upper atmosphere by neutron bombardment of nitrogen 14. On the other hand, the other isotopes used in radioactive ...


3

Current consensus says heat does not affect the rate of radioactive decay and if it does it is due to time dilation, the effect of whihc is very small. Thus the heating of meteorites as they enter Earth's atmosphere will not affect their radiometric dating.


3

From Australian Government- Geoscience AustraliaAustralian Stratigraphic Units Database: Panorama Formation: Paleoarchean min age: 3427 MA Age method: isotopic, U/Pb-Pb/Pb ion probe Dresser Formation: Min Age: Ma: 3477 Age method: inferred, overlying unit McPhee Formation: Min Age: 3477 Age method: isotopic, U/Pb-Pb/Pb ion probe


3

It sounds like there are two primary ones: No, these are not the two "primary ones". The method used depends on what you are dating, and what age you expect it to be. Radiocarbon dating is relevant to things younger than a few tens of thousands of years, and it's only relevant for things that were living (or growing), and incorporated atmospheric carbon. ...


3

Suppose you purify a sample of uranium 238, removing all of the lead. Half of those U-238 atoms will have decayed into lead 4.468 billion years from now. If the lead is removed from that half-uranium/half-lead sample 4.468 billion years from now, half of the U-238 atoms in that purified sample will have decayed into lead in yet another 4.468 billion years. ...


3

The reliability is dependent on the quality, (for instance is the mineral reworked or porous and thus prone to contamination), and size of the sample, (small samples result in poorer measurement). There is also of course the date range issue, use a sample that is too old or too new and the amount of each element is so tiny it can't accurately be measured. ...


3

No, not really. In simple terms, to be soluble in water, Pb must be in contact with it. But most of Pb is stored within the Zircon lattice, where water cannot diffuse through. For example, many zircons in metamorphic and magmatic-hydrothermal settings experience supercritical fluids, but preserve their U/Pb ratios (e.g. inherited cores in metasedimentary ...


2

What exactly are you trying to measure? some of the great North American and Andean batholiths have cooling histories of at least 20 million years, and maybe more than 50 million years. It is perhaps inappropriate to think of the crystallization process as having a single date. Phenocrysts near the top of the pluton are cooler, but may sink to deeper levels ...


2

Many of your questions are answered in this question and associated answers: Why is Earth's age given by dating meteorites rather than its own rocks? To add to some of your other questions: Wouldn't radioactive decay have already been occurring in all of those meteorites long before they hit earth or our moon? Yes. We have an assumption that the ...


2

ScienceMag says: Rather than damaging the fossils by dating them directly, the team looked to the sediments in which they were found. They discovered pieces of charcoal in sediments at similar depths, and considered those to be proxies for the ages of the fossils themselves. The charcoal bits were dated to around 19,000 and 13,000 to 11,000 years before ...


2

Radioactive dating works on specific isotopes we use for specific time frames. Rubidium–strontium dating methods (because this substance has a half life of 50 billion years) to date extremely old geological samples as well as space samples like lunar rocks. Another issue is the quantity of synthetic isotopes in varying samples. Alot of these isotopes do not ...


2

Crude oil is a product of partial degradation of organic matter, e.g. of plants that lived long time ago. During photosynthesis, they constantly incorporate carbon (from $\ce{CO2}$) to accumulate biomass. But carbon is not uniform, it consists of different isotopes, and a tiny fraction of radioactive $\ce{^{14}C}$. Slowly, over time (with a half-life of $\...


1

They microscopically examine drill debris to determine if they are in the target formation , typically coral/marine shells. This is not done for all wells but for exploratory and step-out wells ( expanding a field). Primary interests are gas/oil ratio, hydrocarbon/water ratio, sulfur level. Age is only of interest as it gives information of the other ...


1

In line with what strawberry-sunshine has answered, and to put it into more layman terms, after a compressive episode there's a distensive one. Imagine you have a volume of sand, and you are compressing it horizontally in one direction, it is confined in the other horizontal direction and the only force acting vertically is gravity. During compression, the ...


1

There is always some way of dating a fossil. The problem is not so much in finding a way as in finding an accurate way. Laboratories usually have to deal with incredibly small amounts of material. Take the potassium - argon method for instance. A volcanic tuff will not be pure potassium, it will only contain a trace. Only about one potassium atom in a ...


1

If the fossils, or some of them, were as you describe them with no mineral replacement of the original material, then it would seem that C14 dating would be relevant for the youngest bones at least. If they had original material with adequate carbon in it,C14 is such an obvious method that they must have tried it, or had some very good reason not to. C14 is, ...


Only top voted, non community-wiki answers of a minimum length are eligible