how can fossils be usedto find the relative age of rocks?

Answer 1

Via the firm observation that a particular fossil type ("index fossil") occurs only within certain layers of sedimentary rocks. You can then correlate equivalent layers from one place to another. And via the principle of superposition, you know that layers underneath are always older, and layers on top are always younger (unless there has been over turning, as indicated by way-up indicators etc). Put the whole thing together and you have a relative time scale based on index fossils.

Answer 2

In much the same way one could examine a drawing or photograph of people and by the styles of dress, estimate the decade in which it was taken.

Organism types, and dominant groups have changed radically over time and we can correlate rock units based on fossil content.

If we are fortunate enough to have isotopic pairs in minerals or intrusions that cut across these fossiliferous layers, we can subsequently get an absolute age of those rocks..

Answer 3

Fossils are used to find the absolute ages of some rocks. Once you have the absolute age it is easy to find the relative age. As far as I know this technique is not used, but it could be. Also, Jon gave you some misleading info. Although carbon dating is used to determine the absolute age of carbon bearing rocks, this technique is good only for rocks about 60,000 years old. The vast number of rocks out there are much older, and this method cannot be used on them.

Answer 4

They use carbon dating. Every living thing has a natural level of Carbon-14 in us that begins decaying once we die. It decays at a known rate, so when they dig up fossils and measure the Carbon-14 in it, they can tell how long the animal has been dead. Then they just use this as a measure of how old the rocks are around it, because when it died, thats when the rocks started forming on top of it.

Answer 5

In reality it can't because they have discovered from when Mt St Helen's erupted that something they thought took thousands and thousands of years really could take only as long as little as two years to form. Which messes with their timeline a bit. Also if say a flood happened then the fossils on the bottom would be the smallest ones and would get killed first and covered because the larger animals and creatures could likely climb up as the water rose and as the mud covered what had gone down before it. So they would get covered last as the water and earth materials covered them. SO really no way to tell from the fossils how old rock is.

Answer 6

dont even start with this question! i have a friend who was at a museum, and he asked the scientist "how do u no how old the fossils are?" and the scientist replied "by the layer of rock its found in" and he moved on to the next exhibit and asked "how do u no how old that rock is?" and the scientist said "by the fossils that was found in its rock layer" and he said isn't that circular reasoning? the scientist realizd it was and then attended a church and is now a christian.