No one has observed anything that happened millions or billions of years ago.
I have. I've seen light from 3C273. It left there two billion years ago.
"The wretched world lies now under the tyranny of foolishness; things are believed by Christians of such absurdity as no one ever could aforetime induce the heathen to believe." - Agobard of Lyons, ca. 830 AD
Biology: A Custom Edition for Anoka-Ramsey Community College - 2005 - (Campbell; Reece) Inquiry Into Life - 2003 - (Sylvia Madder)
Campbell's other texts are fairly highly regarded, though I haven't read any of them. Mader's Biology is clearly written and, I thought, a pretty good text. And yes, newer is probably better: biology is moving awfully fast.
Do scientists ever consider the possibility that a bird could come from a chemical soup like some other organisms supposedly did? You know through the process of abiogenesis? (Not a full grown bird, but a cell that develops into a bird.)
That appears to be exactly what happened! It's just that those same first cells also have flatworms and nematodes and trilobites and humans as descendants, too. That's why the DNA of everything alive on Earth looks so very similar, and why all of life here uses the same twenty amino acids.
The only organisms that hopped out of that primordial soup have been dead and gone for about 4,000,000,000 years now: the very difficult task of figuring out what they were like can only be done by comparing the life forms we still can see - the fossils and the biochemical clues in living things.
I need to study the number of positive mutations that would be necessary to be introduced into a population over a given period of time to achieve this transition from reptile to bird.
Keep in mind while you do that the period of time here is in the tens to hundreds of millions of years. And also keep in mind that hens still have the genes to grow teeth - they're just silenced during modern bird development.
An etymology is not a definition, Daniel. "Testify" means to swear an oath upon one's testicles - but they even let women be witnesses in court these days. And besides, for "divine intervention" to exist, the divine would need to exist. I haven't seen it yet.....