Question

FAN AND MEDAL! PLEASE HELP!

This is a really simple Earth Science lab. I just don't really understand it because this textbook is really not well worded. If you give me a hand I will fan and medal! Please please please :)

Here is the link to the lab: http://ocas.pearsonschool.com/ph/cd/0-13-362755-1/iText/phs_hs_earth_main.html?chapter=null&page=433&anchory=null&token=53616c7465645f5fbf38333e581a9d39651d2bb13b72c431e93e7675f5aad2bc2208d27f15e6bb1525d33e130db3f69d3da2c80212744927

Answer 1

Your link is to a portion of a textbook.

What exactly do you want help with?

Answer 2

http://ocas.pearsonschool.com/ph/cd/0-13-362755-1/iText/phs_hs_earth_main.html?chapter=null&page=356&anchory=null&token=53616c7465645f5fbf38333e581a9d39651d2bb13b72c431e93e7675f5aad2bc2208d27f15e6bb1525d33e130db3f69d3da2c80212744927

There it is; Sorry, wrong link. :) @SinginDaCalc2Blues

Answer 3

@ihopethisisfree
Okay ihope...this is the best way to describe this for you.

It looks like your question is really "How can the occurrence of fossils and their known age ranges be used to date rocks?"

The easiest way to think about this would be to think of a giant stack of pancakes! Yummy I know but focus here...

If each pancake represented a different time period, label the stack of pancakes from bottom to top as oldest to youngest...the oldest on the bottom and the youngest at the top.

Now pretend you don't know the labels of the time periods you just gave to the stack of pancakes and set that bit of information aside.

Now you get a knife and a fork and dig down and find a little critter called a "Brachiopod" as shown on your list.

Well since you already know that they only existed between the older Cambrian and younger Devonian periods, you automatically know that the specific pancake you dug it out of HAD TO BE created between the Cambrian and Devonian periods because that little Brachiopod wasn't born yet to be in earlier layers of your pancake stack and it was long dead and could not have been running around doing whatever it used to do in the upper layers!

So based only on finding the Brachiopod in that specific pancake, you automatically know that specific pancake layer in which the critter was found cannot be older than Cambrian and cannot be younger than the Devonian period.

Okay so far? Good!

Now think about this...what if a creature came into existence called a "Gastropod" in the younger Devonian period and died later on in yet an even younger pancake layer called the Pennsylvanian period? That means you could find that creature not only in the Devonian layer of pancakes but also in every layer above that, all the way up until it no longer existed in the layers above the Pennsylvanian period near the top of the pancake stack.

If you can visualize those creatures living in those specific layers of pancakes, then what if your friend wanted to try some of your pancakes and he dug down and found both a Brachiopod and a Gastropod in the same pancake layer?

Well if you knew exactly what layers each creature existed in and they only both co-existed in just one layer, wouldn't it be VERY EASY to see that the only layer they both lived in at the same time would have been the Devonian Period?

So if your friend asked you, "Hey, this pancake tastes old! How old is this pancake I dug down into?"

You could ask him back, "Well did you find any creatures in that specific pancake?"

And then he says, "Why yes, in fact I see both a Brachiopod and a Gastropod in this SPECIFIC pancake!"

Then you could say to him, "Well the only time both of those creatures existed in the same pancake was in the pancake made in the Devonian period, so the age of that Pancake (or rock layer), CAN ONLY BE OF DEVONIAN AGE!"

So your friend gives you a weird look for feeding him stale pancakes, but keeps eating the Devonian Pancake.

Does all this make sense?

So to answer your original question:

"How can the occurrence of fossils and their known age ranges be used to date rocks?"

If you know what time periods different types of fossils were actually alive, and you can find them in the same layers of rocks, you can deduce by elimination which rock layers they DID NOT EXIST TOGETHER IN, and instead narrow down the age of the rock they are both found within!

I hope this help! :o)