A pet peeve about the portrayal of geologic time…
This is quick, random, and a little ranty.
There was a program on PBS last night about early dinosaurs. It seemed a little dated (I don’t know, maybe from the late 80s/early 90s). I wasn’t really watching it…since we don’t have cable we end up watching a lot of PBS (it’s either that or Are You Smarter Than a 5th-Grader, which is a different rant for another time).
Anyway…I really dislike these statements (I’m paraphrasing):
And then the Permian period ended and gave way to the Triassic period. At the same time, a major extinction, a mass extinction occurred.
They make it sound like a coincidence. As if the Permian and Triassic periods somehow exist as fundamental divisions of time. Wrong. The Permian period ends because of the mass extinction. That’s how it’s defined!! I hear this all the time for the K-T as well on these, otherwise fairly enjoyable, popular science programs. It’s not ‘the dinosaurs became extinct at the end of the Cretaceous’ … it’s ‘the end of the Cretaceous is marked by a mass extinction, including dinosaurs’.
It’s not that hard.
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Clastic Detritus 
This annoys me too – it’s like they think geologists randomly split Earth history into chunks which just happened to line up with major changes. Back beyond about 700 million years or so ago it gets much more difficult precisely because it’s harder to identify and correlate such changes.
I have an as-yet-vague idea for a book on this theme: the boundaries, and the changes which define them.