2. IN the Beginning, There was the Mystery: WHAT KILLED OFF THE DINOSAURS? It was thought, based on some geological Evidence, that it was Climate Change – a cooling world, to be general (because it was impossible to be exact)

3. THEN, Luis Alvarez and his Son, Walter Alvarez, begat The Cretaceous/Tertiary (K/T) Boundary Event based on a clay layer in a quarry in Gubbio, Italy, that was Loaded with Iridium. Iridium is found in asteroids, so they theorized that a Mighty asteroid Impact Killed off the Dinosaurs.

4. But where did it happen (if it did)? They searched, and searched… and found the Chicxulub impact structure. It had been hiding in plain sight, the rim defined by the semi- circular pattern of cenotes on Mexico’s Yucatan Peninsula.

5. Just one little problem… Dinosaurs were TOUGH. Could one impact (even a big one) cause sufficiently awful climate change to kill off all the dinosaurs? Various scenarios were invoked, such as a huge continental scale firestorm (which probably happened).

7. Geologists noted that the Chicxulub impact happened near the end of a million-year long period of elevated volcanic activity: the Indian Deccan Traps flood basalt period. Lava flows like this: produced immense layers of basalt as the Indian Plate passed over the Reunion hotspot.

8. And while the Deccan Traps were erupting, the eruption would have had effects something like this: Over a million years, this might be expected to have some effect on the atmosphere.

9. Volcanic effects on the atmosphere & climate Mount Pinatubo, 1991 Ash has an immediate effect; SO 2 a longer-term effect.

10. Timing is everything. Chicxulub is too early … by 300,000 years or so. There still is a K/T boundary and iridium layer, and this is where all the marine biota die off, too. So it might be another impact, or a pulse of higher Deccan Trap volcanic activity. The net result of these factors was a stressed, cooler climate for a million years, with ‘knockout’ blows at the end.

11. The DUST factor Even with elevated volcanic activity, and the occasional asteroid impact, the atmosphere is resilient. Ash and aerosols get rained out and become lower in concentration over time. But their cooling effects persist. Cooler means drier. Drier means dustier. (This is shown in ice cores.) And dustier means iron.

12. Phytoplankton need iron to grow! Experimentally-induced phytoplankton bloom created by adding iron Dust comes from dry land (and also volcanic ash) So cooler climate means more dust goes into the ocean; phytoplankton growth increases; increased ocean primary productivity (photosynthesis) maintains lower atmospheric CO 2 concentrations, keeping the climate cool.

13. And thus: ++ =

14. Epilogue: Dust, CO 2, and temperature Iron in airborne dust acts as Earth’s ‘chemostat’ – keeping cool climate conditions cool. Conversely, less iron means less productivity, allowing higher CO 2 concentrations to persist.

15. The End