"The Gulf Stream is the weakest it's been in more than 1000 years!" "It moves more slowly than it has in 1600 years!" HOW DO THEY KNOW?

As you know through my questions I am always amazed at the confident dating of things by scientists. 7 billion years old. 300 million years ago. More species are extinct than there are in the world. Things like that. HOW DO THEY KNOW? It always sounds so authoritative and assured. If species are extinct do we have evidence of them? Do they all have names? Or can we live and die without leaving a trace? I'm going to ask. I did not know about the California Current Shuhak. Thank you for your informative reply m'dear! :)

They use fossil records to come up with their "facts".  However, since there's no one around now who was there back then to verify their conclusions, some of their "facts" are educated guesses.  They're always "updating" their dinosaur skeletons.  Piecing together bones of something no ones seen is hard.  Bone A and bone B may be from 2 separate animals, but since they were found together, it was assumed that they were form the same animal.

Can things die off and not leave a trace... yes and no.  Everything leaves a trace.  From its excrement to its skeleton.  However, this planet is dynamic.  Its constantly recycling itself.  Old rocks and stuff are pulled down via subduction, and new rock is emitted by volcanic eruptions.  Im sure youve heard of the water cycle (that's water recycling).  Unless something (a tree, an animal, a person) gets trapped in just the right conditions, it all rots back into the ground.  If it didn't, we'd be up to our necks in dead things and there wouldn't be any food (decayed matter feds plants).  Occasionally, a dead body (ot tree) gets trapped by something (volcanic ash, amber, sediment).  Sometimes the body rots away, but it's imprint is left behind in the stuff it was trapped in.  That's a fossil.  Sometimes the material its trapped in wont allow it to rot (ice, sand, tar) and we find bones.

Thank you for your thoughtfully informative reply Shuhak. I appreciate it as usual. In other words sometimes it's a crapshoot! I've heard about carbon dating but haven't really researched it. Also about counting the rings in tree trunks. But who set up those parameters and how do we know they are correct? Each ring represents so many years. Who says so and how does he/she KNOW? Of course I am not a scientist so all of it is magical and mysterious to me. Do we even know how much of what we think we know is guesswork? AARRGGHH! It never ends. My questions. Why do you think so? How do you KNOW so? And so it goes! :)

Trees (very simplified) - As a tree grows up, it also grows out (meaning the trunk gets bigger).  A tree trunk has a hard outer coating (bark).  Beneath the bark is a thin layer called the cambium.  The cambium is what forms branches and helps the tree to heal.  As a tree gets bigger, it needs a bigger cambium layer (much like  a child needs more nutrition as it grows).  So each spring when it’s nice and wet from all the rains, a tree “grows” (expands?) its cambium layer (technical term- cell division).  The old layer becomes a tree ring beneath the new layer.  Then in summer/fall, the tree forms another cambium layer (to get it ready for winter).  The spring ring is paler and the summer/fall rung is darker.  And so it goes, year after year.  Since spring and summer/fall only come once a year, we know that one light ring and one dark ring equal one year.

Oh? Okay then. After one year if they slice open a tree trunk they find one light and one dark ring? So when they cut trees down to use the wood for something they noticed the rings and figured out they meant something? Not just decorative but also informational? Okay then. Thank you for your reply Shuhak! :)