1. Observations
Among the silicate planets, Plate Tectonics is only found on Earth, indicating that special circumstances are required.
Plate Tectonics (kinematic description) = Subduction Tectonics (dynamic description); PT = ST
Subduction requires dense (= cold & thick) lithosphere to sink beneath less-dense asthenosphere. 1) becomes: When did Earth cool off sufficiently to allow ST to begin?
Use geologic evidence to constrain ST start
“Smoking guns” of ST: Ophiolites, Blueschists, and Ultra-High Pressure (UHP) terranes
Abundance of Ophiolites and first appearance of Blueschists and UHP terranes indicate ST/PT began in Neoproterozoic time (~ Ma).
Start of ST/PT affected global climate: Neoproterozoic Snowball Earth

6. …its obviously a quartz monzo diorite!!

8. James Hutton

9. The present is not always the key to the Past ~ James Braid

10. and…..Sometimes the Past is the Key to the Present