One of my New Year’s blogolutions was to clear out my to-blog folder, and bring closure to my unfinished drafts by simply posting them as-is. This is one of those drafts. Disorganized paragraphs, unfinished sentences, and general incoherence enhance the natural character and beauty of a half-written blog post and should not be considered flaws or defects.
Draft date: February 29, 2008
Once you have chosen an event that represents a boundary in the geologic time scale, you are left with two questions: How long did that event take? How accurately can we resolve the date at which it happened?
Time scale boundaries are pinned to some event that left a trace in the geologic record. This event is sometimes big and important, and sometimes seems a little arbitrary. Examples:
- Reversals of the Earth’s magnetic field
- Wiggles in the record of oxygen and/or carbon isotope variations associated with climate change
- A mass extinction
- The first appearance of a particular species in the fossil record
The impact that finished off the dinosaurs was a very fast event, but despite a 20 year old cottage industry devoted to the search for impacts at the root of other mass extinctions, we haven’t found much evidence that instantaneous disasters from space were responsible for any other mass extinctions. It’s also accepted, though the details are uncertain, that the dinosaurs were
Jinet Aut Science 2000/2001
Cortillot and Renne 2003