What you will learn in Geologic Time and Stratigraphy

1. 1. Ordering without numbers

   A cross-section with beds, a fault, an intrusion and an erosion surface, and no dates on anything. The principles you need arrive after you have tried, which is the order they were discovered in.

2. 2. The gaps

   An unconformity is a surface where rock should be and is not. The most famous one has a billion years missing across a contact you can put one hand on.

3. 3. The clock in the rock

   Parent decays, daughter accumulates, and the ratio inverts to an age. Then the awkward question: an age of what? Not of the rock's formation — of the moment the mineral closed.

4. 4. Choosing the right clock

   Eight systems on one logarithmic axis. Carbon-14 on a dinosaur is allowed here, and what comes back is the answer to the commonest thing anybody says about radiometric dating.

5. 5. The isochron

   The standard objection says dating assumes the answer. The isochron measures the assumption instead — and the statistic that decides whether to believe the result is not the age.

6. 6. The scale itself

   Deep time is not a big number, and the calendar year is how you find that out. The module closes on how 4.54 billion years is actually known, which is not from any rock on Earth.