how do you determin the age of rocks and fossils?
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
495022
Examining fossils- they tell us a lot about once living things like appearance & behavior. Fossils include everything from dinosaur bones & eggs to worm burrows, fossilized tracks, fossilized poop, etc.\n\nStratigraphy or the laying down of sediments over time. This tells us a lot about when & where water occurred. Ripple marks & dunes created by winds. Escarpments carved by the ocean.\n\nGeochemistry involves looking at different isotopes to tell what things were like once.
1103175
4 Billion Years old, the oldest rocks (found in Canada and other places) are 4 billion years old.  Possibly all created when a huge planetoid crashed into the newly made earth.  This caused the whole planet to melt, created the moon, and cause the massive ammounts of iron on the earth to sink, due to its high desity and the melted earth, to the the core and create our magnetic field (the reason we can live).
20343
About 250 million yrs.\n\nOne lap ago was the age of the dinosaurs.
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
382215
The Earth is assumed to be about 4.6 billion years old, and unlike what everyone else said, it's not based solely on anything contained on Earth, including carbon dating. The oldest solid material found on Earth is about 4.1 billion years.\n\nThe guess -- and that's all it is, a guess -- is based on the rate of radiological decay of material on Earth and in meteorites found on Earth and around the solar system.\n\nIf you assume that the entire universe is formed from a common pool of matter (the essence of the Big Bang theory is that all material in the universe came from a single, supercondensed source that exploded); if you assume that therefore, all the matter in the universe has been equally distributed in all directions; if you assume that the rates of decay in all radiological material in the universe are consistent regardless of time, their position in the universe, etc.; then you can derive, by comparing the same kind of radiological material from celestial bodies that were not formed in our solar system, bodies that were part of our solar system when it formed, and that material now on Earth, the age that the Earth must be at the time it began to take solid form.\n\nThe paticular materials used to get that age is Lead-206 / Lead-207, which are the products of decay in Uranium-238.\n\nThis is further supported by temperature measurements of the universe and the evidence of background radiation from the timing of the Big Bang, which is assumed to have occurred about 15 billion years ago; given the rate of expansion of the universe visible to us, and the rate of change in both the speed of that expansion, the temperature of the universe and the density of space, we can verify the assumptions of the Earth's age to be within the estimation of a "young Earth" of 4.6 billion years old.\n\nAlso, to the person who said "The Bible": If you derive the history of the Earth from the Bible, as countless theological scholars have done through extensive research, it's about 6,000 years old; no scholarly Biblical research places the age of Earth at more than 10,000 years old.\n\nIf you want to believe that, in the face of overwhelming evidence to the contrary, that's fine. But you should at least agree with your evidence before citing it.
1066565
Although some of the answers you have received are accurate they aren’t exactly succinct or to the point.\nYou haven’t however said what age the kids are you need to explain it to, please forgive me if this explanation seems too simplistic.\nThe theory of radioactive dating works along these lines.\n\n1. SOME ELEMENTS “DECAY” (CHANGE) FROM ONE THING TO ANOTHER, e.g. from Potassium to Argon or from one isotope to another e.g. C14 to C12\n2. THIS RATE OF CHANGE IS KNOWN, the speed at which it changes is known as the half life, i.e. how long before half of the total has changed\n3. A COMPARISON IS MADE i.e. you work out how much there was and how much has changed\n4. THE AGE IS CALCULATED. Once you know how much has decayed you can compare the amounts on well-known charts e.g. if you know halve the amount of C14 has changed to C12 then the sample is 5730 years old.\n\nIt is considered accurate because the rate of radioactive decay is absolute, measurable and observable. It has been tested numerous times and can be experimented on. The same results can be achieved and repeated by numerous people at many different labs. On the whole the decayed products (e.g. C12 etc.) are not found naturally. The original material is created at the time the sample is formed or moved (e.g. when the plant, animal grew).\n\nHowever the problems are\n1. In order to calculate the percentage of element changed you have to know how much there was. Sometimes the sample can have some of the original material removed or more of the original material can be added, e.g. new living fungi can grow and die on a log hundreds of years after the log was originally felled and buried.( this would give a younger date)\n2. The resulting product can be removed or further altered e.g. Argon from potassium can escape as it is a gas ( this would give you a later date because it would seem not as much or the argon had been formed)\n3. This time clock can be reset due to outside influences. A fire can reset the amount of C14/C12 because the carbon from the fire is different from the carbon formed in the living thing (e.g. the problems with dating the shroud of Turin)\n\nThis of coarse assumes that the equipment used is accurate and that no contamination was added e.g. someone touching or sneezing on the sample.\n\nOn the whole though in theory the method should be extremely accurate. Given perfect samples, good laboratory practice and accurate measurements the results seem impressive. This shouldn’t automatically however be taken for granted.\n\nThe final thing to remember though is that there is no other way of giving empirical, measurable dates on extremely ancient rocks or artefacts.
1092991
Try a museum of natural science.  You can find all kinds of fossils there.
414512
As soon as a living organism dies, it stops taking in new carbon. The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. \nA formula to calculate how old a sample is by carbon-14 dating is: \n\n\nt = [ ln (Nf/No) / (-0.693) ] x t1/2 \nwhere ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years). \n\nSo, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: \n\n\nt = [ ln (0.10) / (-0.693) ] x 5,700 years \nt = [ (-2.303) / (-0.693) ] x 5,700 years \n\nt = [ 3.323 ] x 5,700 years \n\nt = 18,940 years old \n\nBecause the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old. However, the principle of carbon-14 dating applies to other isotopes as well. Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years. Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).
587794
There are actually many ways to date the rocks. One well-known way is carbon-dating.\n\nOne great site is:\nhttp://archserve.id.ucsb.edu/Anth3/Courseware/Chronology/01_Contents.html\n\nThis site has short summaries for each method-- no need to read a scientific journal artical for each method.
949488
Radiometric dating is extremely reliable when it is used correctly. Anti-science propagandists like to pick out the few examples where the technique was misused in order to give the impression that the technique itself is flawed (their favorites are carbon-dating mistakes where the user didn't consider - or was actually testing - the 'reservoir effect'). This example however, is worse, as it is a case of deliberate misuse of the technique by a Creation 'scientist'.\n\nYes, it is true that the rocks produced such 'ages'. HOWEVER, dacite is a porphyritic rock - it contains xenocrysts of older crystals. But more importantly, Steven A. Austin (I'll name and shame) sent the samples to a lab which clearly states that their Potassium-Argon equipment cannot accurately measure samples less than two million years old!! Hence he deliberately mis-used the technique for propaganda and deception value. Disgraceful.\n\nAs well as the excellent links given above, it is worth emphasizing that  there are dozens of different isotopes, with different half-lives, that can be used in radiometric dating. The different decay curves always converge on the same ages (when used as they are supposed to be used), a mathematical impossibility if there was a problem with the method.
696439
Index fossils should occur over a broad geographic range and a very limited time span.  If a group of fossils occurred over the broad range you mention above...they would be lousy index fossils..\n\nThe whole idea of an index fossil is that if you were to find one in the rock record that you would know it occurred at a very restricted time..this identifying that layer of rock as that particular time.  the time range you have listed above covers the entire geologic history of the world except the pre-cambrian.\nthe answer to your question is no.
1018700
The fossilization process begins at the time of an organism's death. Rapid burial under sediments is key for the fossilization process to begin. This prevents decomp from bacteria & protects the carcass from scavengers.\n\nAfter the intial process, it will take thousands of years for a fossil to form. Fossils occur in sedimentary environments. This usually involves lots of water & the deposition of sediments over lengthy amounts of time.\n\nLayer after layer is deposited until the pressure squeezes the water out & lithifies the rock.\n\nSome replacement of bones & teeth may take place. In this process, minerals replace other minerals in the hard parts of an organism.\n\nHard parts are usually the only thing to survive the fossilization process. Soft parts decompose too easily.
61902
Earth is thought to be between 4.5 and 4.8 billion years old. The age of Earth is found by measuring the age of very old Earth rocks. This is done by measuring the rate at which elements of the radioactive metal uranium decay (break down) into lead. Scientists have also measured the age of meteorites which have fallen onto Earth's surface, and the age of moon rocks brought back by the Apollo astronauts. Both the meteorites and the moon formed around the same time as Earth, and they show similar ages.\n\nIf you want a break down of that timespan in terms of Geologic Periods, see:\nhttp://www.cotf.edu/ete/modules/msese/earthsysflr/geotime.html
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?
834832
About  555-563 million years old:\n\nzircon U-Pb SHRIMP(sensitive high resolution ion microprobe) geochronological data :  Pão de Açúcar  gneissic granite-- ages of 559 ±4 Ma (million of years ago) \n\n http://sbgeo.org.br/rgb/vol33_down/3302/1381.pdf.\n\nZIRCON U-Pb SHRIMP DATING OF THE SERRA DOS ÓRGÃOS AND RIO DE JANEIRO GNEISSIC GRANITIC SUITES: IMPLICATIONS FOR THE (560 Ma) BRASILIANO/PAN-AFRICAN COLLAGE*  \nRevista Brasileira de Geociências, Luiz Carlos da Silva et al,\n33(2):p237-244, junho de 2003
858820
Some rocks are formed from magma (lava) that comes from deep in the earth. THose rocks never have fossils because, hey, they were like, 2000 degrees and anything close to them was burned totally. \n\nSome rocks were formed from deposits at the bottom of ponds, rivers, mud flats along the ocean, and in the shallow ocean. Those kinds of rocks (shale, limestone) can have lots of fossils. Let's say that you had a pond at the end of a river where it meets the sea. Lots of dead stuff could float down the river and get caught in the mud. Then it would gradually get covered by more mud. After thousands or millions of years the mud would be really thick. It would be formed into rocks with the remains of the dead animals in it. Bingo. That's a fossil. \n\nThere are lots of grat books about fossils. Check it out at your local library. And most places in the USA there are rocks near you where you could go and dig up your own fossils. That would be cool.