how can they know if a dinosaur lived so and so years ago

[Onceler]

I see this a lot they find a fossil(not just dinosaurs)and say it lived between so many years and so many years ago.How do they know it is between so many years?

 

[dalu]

Cause they are scientist.

 

[Gibsons]

One method is through radioisotopes. wiki

 

[Onceler]

what I am asking is how do they know it was from, to

 

[Cogman]

Originally posted by: Onceler
what I am asking is how do they know it was from, to

Wait, What? Are you trying to infer the some random guy likes to make elaborate fake bones and bury them across the earth for scientists to find? Or are you inferring that many animals and minerals after they die decide to stand up and walk to different contents?

Radioisotopes is the most common method of determining the age of something. Others include measuring the layers of rocks surrounding the fossil and determining how fast one layer takes to form. The latter is less accurate, but available if needed.

 

[silverpig]

Originally posted by: Onceler
what I am asking is how do they know it was from, to

The "from" and "to" parts are usually done with the rock layer method. The date is generally determined via radioisotopes to put it in a period of earth's history. Let's say it looks like this:


LAYER 1
---------
LAYER 2
---------
LAYER 3 - Fossil
---------
LAYER 4
---------
LAYER5

The oldest layer is at the bottom, the youngest at the top. Now, from a lot of other measurements you can generally get a good idea of the dates the layers were deposited. From looking at fossils you can tell what kind of life was there.

Now, let's say LAYER 5 shows a whole ton of life. Lots of fossils. However, when you look at LAYER 4, you see very few of the same fossils as in LAYER 5, and fewer fossils in general. This means that an extinction event probably occurred at the end of LAYER 5. Now let's say the same kind of thing happened between LAYER 2 and LAYER 1. You will then be able to determine that a mass extinction event occurred between those layers as well, and can say with a decent chance of being right that the life that appeared in LAYERS 4,3,2 were largely confined to those layers, didn't exist in LAYER 5, and didn't make it to see LAYER 1. Of course you can then go back to your database of measurements and see that LAYERS 4,3,2 spanned a time from 325 million years ago to 200 million years ago.

Thus, you can say with a good chance that the animal that made your fossil probably lived from 325 million years ago to 200 million years ago.

 

[Onceler]

ok that makes sense with more than one fossil
Thanks silver

 

[spikespiegal]

However, when you look at LAYER 4, you see very few of the same fossils as in LAYER 5, and fewer fossils in general.

Watcha talkin' about?

The Creationists Museum shows human footprints along side them dinosaur ones.

:evil:

 

[Duwelon]

Originally posted by: spikespiegal

However, when you look at LAYER 4, you see very few of the same fossils as in LAYER 5, and fewer fossils in general.

Watcha talkin' about?

The Creationists Museum shows human footprints along side them dinosaur ones.

:evil:

And when a scientist or whoever found it, they said "if we didn't know any better, we'd say a human lived alongside a dinosaur!"

 

[BladeVenom]

Read about the Coelacanth before you take any of those fossil dates too seriously.

 

[Gibsons]

Are the creationists trolling HT again?

 

[bobross419]

Originally posted by: BladeVenom
Read about the Coelacanth before you take any of those fossil dates too seriously.

Granted, Wikipedia is by no means a scientific journal, but I'm having a hard time figuring out what coelacanth have to do with the validity of fossil dating.

 

[BladeVenom]

Originally posted by: bobross419

Originally posted by: BladeVenom
Read about the Coelacanth before you take any of those fossil dates too seriously.

Granted, Wikipedia is by no means a scientific journal, but I'm having a hard time figuring out what coelacanth have to do with the validity of fossil dating.

Because at one time they claimed they died out 100's of millions of years ago. They obviously didn't. I wasn't talking about carbon dating, but the years during which they are guessed at living in, "...it lived between so many years and so many years ago..." The fossil record is mostly incomplete.

 

[bobross419]

Originally posted by: BladeVenom

Originally posted by: bobross419

Originally posted by: BladeVenom
Read about the Coelacanth before you take any of those fossil dates too seriously.

Granted, Wikipedia is by no means a scientific journal, but I'm having a hard time figuring out what coelacanth have to do with the validity of fossil dating.

Because at one time they claimed they died out 100's of millions of years ago. They obviously didn't. I wasn't talking about carbon dating, but the years during which they are guessed at living in, "...it lived between so many years and so many years ago..." The fossil record is mostly incomplete.

Sorry for not understanding, but what does this really have to do with fossil dating? If a bone is from x years ago, then the fact that they didn't find any dating from x years ago until present day does not impact the validity of the original date. Scientists made an educated guess on the duration of the coelacanths' existence and were wrong.

In the wikipedia article I linked it does indicate that "The most likely reason for the gap is the taxon having become extinct in shallow waters. Deep-water fossils are only rarely lifted to levels where paleontologists can recover them, making most deep-water taxa disappear from the fossil record". This makes quite a bit of sense and would indicate why scientists believed the coelacanth to be extinct until the rediscovery during the last century.

There is a lot of scientific information that is based on educated guesses... without time machines this is often the only way to provide information with any sense of accuracy.



Edit - Ah... I reread your post and understand what you are referring to. Again it all comes down to educated guesses which is really all that we are able to do without being able to physically go back to that time frame. Scientists can be wrong, but we have to go with the best available information that we have.

 

[DSF]

In terms of the "from...to" question, it should also be noted that radiometric dates are not actually provided as a single point in time. When you send a sample to the lab, they don't reply with a letter saying your specimen is 45 million years old. They report, for example, that the fossil is most likely 45 million years old, with a standard deviation of 3 million years.

Technically, a specimen dated at 40,000 years old via carbon dating could be anywhere from 30,000 to 50,000 years old depending on the quality of the sample. That's why anthropologists, paleontologists, and others who work with prehistoric remains try to use as many different dating methods on a given specimen as possible.

 

[Onceler]

Originally posted by: DSF
In terms of the "from...to" question, it should also be noted that radiometric dates are not actually provided as a single point in time. When you send a sample to the lab, they don't reply with a letter saying your specimen is 45 million years old. They report, for example, that the fossil is most likely 45 million years old, with a standard deviation of 3 million years.

Technically, a specimen dated at 40,000 years old via carbon dating could be anywhere from 30,000 to 50,000 years old depending on the quality of the sample. That's why anthropologists, paleontologists, and others who work with prehistoric remains try to use as many different dating methods on a given specimen as possible.

ok this makes the most sense so they are not saying that something lived at 500 to 200 million years ago they are saying that it lived between those times because it could be anywhere in between,ok I was misinterpreting what I was reading