Reading strata
Every layer is a page; every bed a season that settled and stayed.
Sedimentary rock is laid down in beds, one on top of another, and it never lies — the oldest bed is at the bottom, the youngest on top. Reading strata is reading time from the bottom up.
What a bed tells you
thickness how long the conditions held grain size how fast the water moved fossils what lived, and when colour how much oxygen, how much iron
The rule
Superposition: younger sits on older. Fold a mountain over and the beds will still tell you the story, because the order never changes — you just have to work out which way is up first.
