Originally posted by vivify
Occasionally, I'll see an article mention some organism as "unchanged for millions of years", like this sea creature, which is said to have remained unchanged for 500 millions years, seen here:

http://news.discovery.com/animals/sea-creature-has-lived-the-same-way-for-500-million-years-120911.htm

How do scientists determine an "unchanged organism", or how long it's been since the last time it "changed"?

Thanks for any help.

They can determine it is unchanged by comparing all the fossil remains of the sea creature with the present day sea creature. However, they can't really tell how long it has remained unchanged. But the 500 million years comes from the uniformitarian evolution theory in geology.

http://education-portal.com/academy/lesson/theories-of-geological-evolution-catastrophism-vs-uniformitarianism.html#lesson

Check out the thread "How Evolutionists Date Rocks and Fossils" for more information.

Originally posted by vivify
Occasionally, I'll see an article mention some organism as "unchanged for millions of years", like this sea creature, which is said to have remained unchanged for 500 millions years, seen here:

http://news.discovery.com/animals/sea-creature-has-lived-the-same-way-for-500-million-years-120911.htm

How do scientists determine an "unchanged organism", or how long it's been since the last time it "changed"?

Thanks for any help.

Although the link doesn't make it clear how they determined this in this particular case, I assume it is by the dated fossils as this is usually how that is determined.
You should note that what they mean by "change" in this particular context is, slightly confusingly, how often does a new species evolve from them rather than how much the original species itself changes.
So, when they say this species hasn't "changed" for many millions of years, what they actually mean is that, unlike many other related species, no other species has been known to evolve from it and it has outlasted many other species that have evolved into many other species.

P.S. ignore whatever RJHinds says about anything including this because he is a moron that pretends to know (or is so arrogantly delusional to actually believe -not sure which ) all about science and better than us scientists when he in fact has NO scientific credentials (and he is certainly extremely far from being a scientists! ) and has repeatedly demonstrated he actually understands NOTHING about real science and is here just to troll/bully and push his extremist religious (creationist in this case ) agenda.
He should be permanently banned from this forum but, given that will not happen anytime soon, I advise everyone not to ever respond to anything he says or even read anything he says because, if you read is stupid moronic posts, there is the unfortunate overwhelming temptation of pointing out their stupidity but then you will just fall into his hands.
He is just a massive time waster.
Don't feed the troll.