How age of fossils calculated?
613541
No, no, no!   It is *not* carbon dating!  This is a common misconception (happily encouraged by creationists).\n\nCarbon dating (or radiocarbon dating) is just one of *many* forms of radiometric dating (but only useful up to about 60,000 years ago and thus is practically useless for most fossils).\n\nAnd radiometric dating is just one of *many* forms of dating fossils and rocks.\n\nBesides radiometric dating, other methods are dendrochronology (matching tree rings in wooden artifacts), paleomagnetic dating (the reversals in the earth's magnetic field), ice cores, varves (counting layers of sedimentary deposits), superposition, stratigraphy, etc. etc.  All of these are good for dating overlapping time ranges ... and where the ranges overlap they confirm and calibrate each other.  (My first link under Sources gives a great overview of many of these different methods.)\n\nCarbon dating is used for dating once-living tissue like bones or wood (*not* fossils) and is very accurate, but only to about 50,000 to 60,000 years ago ... much younger than most fossils.  Why?  Because carbon-14 decays with a very short half-life of only 5,730 years (which is why it is so accurate).  For dating older artifacts like fossils, we use isotopes of radioactive materials that decay with a much longer half-life.  Each technique is named after an atom that decays at a known rate (half-life) into another atom.  For example, potassium-argon dating measures the decay of potassium-40 to argon-40 with a half life of 1.26 *billion* years.  There are literally dozens of other methods, and again, because they overlap, they all confirm and calibrate each other.
851623
Earth's age is based on several things:\n\n1) dating meteorites. When we find a meteorite from this solar system that has a similar composition to earth, you get many young ages, but the oldest and most common date to 4.6 Ga (billion years).\n\n2) isotope trends. When you look at certain radiogenic isotope ratios that change with time, like Rb/Sr or U/Pb, you find that many rocks with differnt ratios of many ages form a line, and the line traces back to an origin of 4.6 Ga as well.\n\nThe oldest life is 3 1/2 Ga, the oldest rock is about 4 Ga, and the oldest date ever found is on the highly durable mineral Zircon from Australia, it's date is 4.2 Ga. So, there is no direct method, it is based on inferences. However, many different inferences lead to the same number 4.559 Ga (to be specific).\n\nYou would have to throw out everything we know and love about Geology to accept a young earth view. When you look at the Grand Canyon, how can you say that only took 6000 years to form?
976654
Looking at astoriods because the whole solar system was formed from the same stuff and the rocked in the Earth is being renewed by subduction a creation zones so you can never tell how old that rock is because it will have been remade many times since the formation of the Earth.\n Radioactive dating not the most accurate but radioactive particles are in everything and they all decay so you can tell how old something is by looking at how much the radioactive particles have decayed \nalso there is carbon dating. You have to set things on fire for this so obviously you cnt do this on everything so it's not terribly accurate \nALSO I'M ONLY 12 YEARS OLD
164705
You can 'guess-timate' a turtle's age by counting the rings on the scales (scutes) on the belly (plastron). Note that this does not work on very young animals (no rings yet), very old animals (too many rings crowded too closely to count well), turtles that have very smooth plastrons (Snappers, softshells), or turtles whose plastrons are very worn.\n\nThis works because they add one ring every time they shed a scute- usually one per growing season. Even the tropical species only tend to have one rowing aseason per year.  \n\nThe technique is to count the rings on at least four different scutes. Whichever number you come up with the most often is the approximate age.\n\nIt is only an APPROXIMATE age because they can easily skip a year or two (especially when fully grown), or shed a few times a year (especially when young and growing fast). In a bad year, the rings might be hard to see, or a 'false ring' may develop because of a disease, etc.\n\nSome researchers have created a chart that works for some species, sorta. For example I have seen one for some species of Box turle that treats the first five rings as two years, then rings after 10 as two years each- all of which assumes that the rings are reasonably regular and a certain space exists between them, etc.\n\nSome species develop strong rings in the scutes of the back (carapace). These rarely match up with the plastron count.\n\nNow, except for natural curiosity, there is not much reason to know the actual age of a turtle. With most species, you determine adulthood more by size than a guesstimated age. \n\nThere is also a tendency to think that most turtles are really old- but the average lifespan of many turtles is well under 20 years. The really old turtles are generally tortoises and almost always live in very protected places. The last documented longevity record for a Painted turtle that I have seen, for example, is only 22 years- and it was born and raised in a zoo.
1076632
The likely hood of your ending up as a fossil is extremely rare. In 99.9999+% of cases your body will just decay. Of those .0001 percent that do fossilize only about .0001 percent of those will ever be found. Really the only reason we find any fossils at all is because the earth is so incredibly old.
311743
Certain substances have a radioactive halflife.  That means it takes a certain amount of time for that substance to decay so far.  Carbon dating is the process of observing the decay of the carbon present in an object to determine its age.\n\nLike any scientific property, there is always error.  The equation and theory models very close to reality but never exactly.  And there are so many other things that could've assisted in the decay which result in incorrect data.\n\nWhich is why whenever you want to make a scientific claim about certain fossils containing carbon for example, you will take many samples from various objects within a certain layer of the soil, then take the average age of them all, giving a rough estimate of the age of that particular layer of soil.\n\nIs carbon dating perfect?  No.  No scientific method is without errors.  But if done intelligently it can give reliable statistics about the age of objects.\n\nMost of the people who are wholly against carbon dating point out errors and flaws with it that any reasonable scientist is fully aware of and they pretend that it's a profound problem which invalidates the whole process.  The majority of Carbon Dating critics are coming from the religious front, who oppose it because it disproves their beliefs.\n\nUltimately though, if done by a careful scientist with lots of samples, then averaged, carbon dating is generally reliable.
325178
Silurian (440 to 410 million years ago)\n    * First land plants\n\n\nSource: \nFossils and the geological timescale\nhttp://en.wikipedia.org/wiki/Fossils_and_the_geological_timescale
586716
Here are some really basic notes, i don't know what grade you are in, i'm is 6th\n\nFirst, a fossil is made by:\n\n1.  the animal dies and lays on usually sand and mud\n2.  any living objects have calcium\n3.  later, the skins and other parts are rotted and faded away.  \n4.  only the solid, bone, is left\n5.  new sediment covers it\n6.  then the water or whatever goes down into the sediment.  \n7.  the minerals of the water then fills in any gaps and hardens\n8.  the bone or solid will then be replaced by the minerals that are harden\n9.  a replica of the bone is made\n\nremember that a fossil is not a bone\n\na fossil is a replica, copy, of a bone\n\na fossil is a rock\n\narchaeolgist then puts the fossils together to get a view of the organism that has onced lived.\n\nmany things count on fossils, like what type of animals lived.  or even how migrators moved.  footprints are also can be a type of fossil...\nwww.diamondgemztone.piczo.com\n<>dia gemz\nsheri
892212
Around 4 billion years old.
664667
All fossils should have some Carbon-14, but hypothetically, if one didn't, a different radioactive isotope could be used to determine the age of a fossil.
1123972
The length of the year was about the same. The day has gotten a bit longer, so there were around 400 days in a year around 200 million years ago. For fossils only 6.5 million years old, there wouldn't be much difference (perhaps a day or two per year).
968818
Shanna and Geo06 have got this just about right.  The only thing I can add is that radiocarbon dating can not be used for more than about 70,000 years ago, and is more accurate for living things that died within the last 8,000 years.\n\nMost geologists measure rock ages in millions, or even billions, of years, so the age of the earth and the age of almost all igneous rocks is well beyond the range of carbon dating.  On top of that, igneous rocks contain very little if any carbon,  so carbon dating is not applicable here.  \n\nSo the only thing carbon 14 can be used for is to determine the time that an exchange of carbon with the atmosphere stopped, ie, the death of a living thing - the third item on your list of choices for your homework.\n\nThe half life of C-14, the radioactive isotope of carbon, is about 5730 years.  Therefore, if you know the ratio between C-14 and C-12 in the atmosphere when the organism died, and you know the ratio now, the difference in the ratio can be calculated backwards, using the half life, to estimate when the organism died. \n\nAtmospheric C-14 has not been in a constant ratio with C-12, as previously thought, so there are some serious problems with the accuracy of C-14 dating.  The problem is that the natural ratio of the carbon isotopes in the atmosphere (carbon dioxide) varies because cosmic ray bombardment of the outer atmosphere produces C-14 but not C-12.  The ratio can be predicted accurately using the ratios in old trees, where the tree rings can be used to accurately determine the age of each ring with its annual ratio, with a maximum of about 8,000 years -that's how old the oldest trees are which can establish a reference ratio.\n\nDating of artifacts is a best guess, the best method is to measure the amount of lichens growing on them, or the age of carbon in ashes found in the same spot.
319576
It's the study of fossils.
247560
It depend if you are a religions person or believe in facts. Me, as a geologist I believe in facts and science.\nThe earth forms 4.6 billions years ago. How did we know? By using the radioactive decay method. \nNobody really knows how it form but you can get differrent references. Try historical geology books. \nEarth solidifies around 3 billion years ago, how? From the dated rocks namely Banded Iron Deposits. Life began at PreCambrain era. Meaning 512 millions years ago. Dinosaurs came to life at least 100 million years ago and died 65 miilion years ago because of  a comet hitting the earth.\nActually there are a lot more happend but for your satisfaction try to look for a Historical geology book. A very interesting book.
144124
One common element that is found on this planet is Carbon. So they study the Half-Life of Radioactive isotopes to comeup with the age of a thing. Before the radioactivity method was discovered, scientists used early method. There is a formula that scientists used (Before the discovery of radioactivity method), which was first derived by Kelvin.\nHere is the formula. \n"\nAge = (To - T)2/ ( pi*K*GG2), \n\nwhere To is the formation temperature, T is today's temperature, pi is 3.14, K is a material property called thermal diffusivity (we'll use 1mm2/sec) and GG is the Earth's geothermal gradient (25 C/km). If To ranges from 1500 to 2000 C, the age of the earth would range from 36-65 m.y." - Courtesy: http://www.globalchange.umich.edu/ \n\nOfcourse, after discovering Radiogenic age determining methods, the way of measuring Age of things has changed.\nHere is the link that has more information of Radiogenic dating methods.\nhttp://www.globalchange.umich.edu/globalchange1/current/lectures/clocks_in_rocks/clocks_in_rocks.html\n\nhttp://www.ucmp.berkeley.edu/fosrec/McKinney.html
175894
The bible is wrong. It was written by people who didn't know the science.\n\nMost fossils are NOT dated using carbon dating. Why not? Because it is useless for ages more than about 100,000 years. Most fossils are much, much older than that. Usually either potassium-argon, rubidium-strontium, or uranium series dating is used. These don't have the difficulties associated with carbon dating and are self-correcting in the sense that they will let you know if a sample is contaminated.\n\nThe earth is about 5 *billion* years old, which is much older than 40 million, which is much more than 12,000.
1068442
There are a lot of different dating techniques.  (The second link talks about some) Usually, when dating something, you don't just use one technique one one sample--you try to find a few different ways, and use them to build up a case for the age of something.\n\nSome dating systems are relative, in that they can only tell you which came first.  This is useful because it lets people assemble a chronology of things, even though it won't have absolute dates.  Once you have this chronology, you can use absolute dates to start finding approximate ages for things. For example, there's a distinctive layer of iridium in many rocks. If you find something below that layer, it's a good bet that it's older than the layer is.  Once you know that the layer was put down about 65 million years ago, you can start to narrow down the date of the things beneath it.\n\nRelative techinques are also useful as a test for the absolute techniques--if you know what order things happened in, you can use that to check that other techniques are giving sensible results.\n\nThere are also a lot of different absolute techniques--see the third link for a disscussion. Some, like counting tree rings, are very accurate, but only go back a few hundred or thousand years. Others, like carbon-14 dating, work on things that were once alive.  Still others, like Uranium-Thorium dating or archaeomagnetism, only work on certain kinds of rocks. Carbon-14 and U-T dating work by looking at how much radioactive materials in the sample have broken down, and archaeomagnetism works because the Earth's magnetic field has changed over the ages, leaving signs in some minerals.\n\nFinally, you can just look at the things that are near a sample.  So, if an archelogical dig contains a kind of pottery that you know was used 3000 years ago, that's a clue that the site is about that old.  If a layer of rock is full of fossils of animals that lived 300-200 million years ago, the rock was probably formed around then.