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gregloa using is or did rather than might or may have been
Ohhh, i think you're pretty wrong about that.
Scientists tend, in my experience, to you use pretty careful language. I think you'll find a lot of declarative statements in documentaries and such but in actual scientific literature you will definitely be seeing language like "it appears", "the evidence suggests", "we think" etc.
For instance carbon dating. Radioactive decay of carbon 14 has a half life of about 5730 years. Anything older than this has such a minimal amount of carbon left that accuracy is non existent and contamination is absolute. So anything scientists say is millions of years old is at best a very far fetched guess
I see this a lot when discussing radiometric dating.
Carbon dating is used to date things from several centuries old to about 50-70,000 years old. And we know it's accurate in that range because scientists have used it to corroborate historical events like the eruption of Mount Vesuvius. The dates achieved from carbon dating samples from sites like Pompeii match the historical dates of the eruption.
But what about things that go beyond that upper limit of 70,000 years?
Well that's why i mentioned radiometric dating at the top: Carbon dating is not the only radio isotope scientists use to date things. There are other elements with longer half lives that are used to date older things.
How do we know they are reliable though???
Because they can be checked against other measure like tree rings and ice varves and all converge on the same time period. That is to say there are independent lines of evidence which corroborate each other.
So the only real proof they have of how old anything is is about 6000 years old.
Forget about radiometric dating, we know just using tree rings that there is far more time than 6,000 or even 10,000 years of history on earth.
How?
We know tree's lay down rings about once per season. There is some variation in that which we can get into if you want but it is a very reliable record overall. Additionally, we can detect in those rings seasons of good growth, poor growth, fires etc. and we can match those rings with younger and older trees.
That is to say, we need not find a 10,000 year old tree if we can find 10 trees overlapping in life times. And beyond that we can find a tree with so many rings which was felled and used in buildings which can then be dated to several thousand years so we know the tree grew even older than that!
