How do we know how old the earth is??

Question

DO we really date the layers by the fossils and the fossils by which layer they are in?! who set the standards and how?

Answer 1

No, this is a lie told by the creationists.

Rocks are found in layers. Some layers are igneous, which means they are composed of solidified lava from volcanoes etc. A good example is granite. We can reliably date these layers using radiometric methods such as argon-potassium and argon-argon. These methods work.

Other layers are what's known as sedimentary. This means they are composed of small particles which settled slowly over many many years. Limestone and chalk are examples. We can't use radiometric methods to date these, as they would only show when the original particle was formed, not when the layer was actually laid down.

However, one characteristic of sedimentary layers is that they contain lots of fossils. (In fact, they are *mainly* composed of fossils!) So we can use a clever trick. If we find a layer of sedimentary fossil-containing rock sandwiched between two layers of igneous rock, we can date the rocks either side and get a good idea of the date range for the fossils. Now, if one set of fossils is always found in rocks that we know to be a certain age, they are known as "index fossils". The next time we find some rock containing these index fossils, it is a fairly good bet that we can date it to the same range as the places we have already found them, whose dates we already know.

For a good and fun read about how we know all this stuff, I recommend Bill Bryon's A Brief History Of Everything.

Answer 2

Try existing ratios of Uranium 238 and Uranium 235 isotopes- its about 138:1 U238 and U235 were both formed about the same time in supernovas with initial abundances U238/U235=about 0.6

Half-life U238 and U235 are 4.47 and 0.7 B years respectively

A=Aoexp(-tln2/4.47) and a=aoexp(-tln2/0.7) represent their decay rates

>138= 0.6*exp((tln2)*(1/0.7-1/4.47))

>ln230=t*0.693(1/0.7-1/4.47)

>t=6.52B yr for original formation of isotopes

This is well within the possible time-frame for the accretion  of the nebular gas and dust to form a planetary solar system about 5 B yrs ago.

Further evidence is the site of a 'natural' enriched graphite moderated reactor at Okolo in the Gabon..this could only occur when the ratio of U238/U235 was about 44:1 or less..ie about 1.5B yrs ago or more! (this correlates with Ar-Ar or K-Ar radiometric dating from the surrounding strata)

I would be very interested in seeing actual evidence to contradict this

Answer 3

its the number of trees x the number of sand divided by the number of people x the number of questions to the eighth power.

Answer 4

Carbon dating is one source of history clarification. Elements decay at a particular rate, and if we can determine that rate then we can begin to consider how old the oldest samples we have found are. Chemical decay is an exponential model and we can create an estimate model for exponents using as few as 2 points in time and their associated ages.

Answer 5

The actual total age of the Earth is worked out by doing long and short lived isotope dating on meteiorites- CAIs zircon refractory inclusions to be precise, since these are the oldest objects in the solar system and haven't ever undergone melting to reset their isotope ratios.

To get the age of layers of rocks it was originaly done purely relatively. That fossil X lived before fossil Y and so the layer that  was in was older than the layer Y was in. This can then be transfered to different geological settings and we can see that the fossil record pattern of species can be used to date rocks relatively.

Nowadays we have a fixed scale on the matter by radioactive dating of the layers the rocks are in. So by saying all layers that have X in are from and age range on A-B whenever I find a rock with X in it, it must come from an age range A-B.

Answer 6

we dont know anything really acutely i mean, N dont know much but the scientist decide.

Answer 7

my science teacher said about 4.5 billion

Answer 8

Fossils in the layers are one way to determine the age of them, but they are not always the determining factor.  Some layers can be transformed by various processes (erosion, orogeny, volcanism); therefore, other methods are also used like radioactive decay.

There are several radioactive decay dating method, such uranium-235/238 lead method and potassium – argon method.  Carbon dating is not used in determining the age of our planet, but minerals like Zircon. Zircon is extremely stable; hence, easily to calculate the trapped uranium to lead decay in this mineral.   Other methods of radioactive decay will yield almost the same number determining material age.  Since science has a way to calculate the years it takes for material to decay, this way we know, how old the Earth is, and the surrounding Solar system.

There are several organizations that set standards and determine proper scientific methods and publications.  These organizations are here well over century and the participants include governments, universities, and research institutes.  They are deciding authority in research and publication; therefore, they set standards for naming various geological epochs and its dating, etc…