Dinosaurs and dust: Decline and demise

How an unfortunate timing of events doomed the dinos and gave mammals a chance

IN the Beginning, There was the Mystery:

WHAT KILLED OFF THE DINOSAURS?

It was thought, based on some geologicalEvidence, that it was Climate Change –a cooling world, to be general(because it was impossible to be exact)

THEN, Luis Alvarez and his Son,Walter Alvarez, begatThe 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 ImpactKilled off the Dinosaurs.

But where did it happen (if it did)?

They searched, and searched… and found the Chicxulub impact structure.

It had been hiding in plainsight, the rimdefined by the semi-circular patternof cenotes onMexico’s Yucatan Peninsula.

Just one little problem…

Dinosaurs were TOUGH.

Could one impact(even a big one)cause sufficientlyawful climate change to kill offall the dinosaurs?

Various scenarios were invoked, suchas a huge continentalscale firestorm (whichprobably happened).

And one other problem…Asteroids aren’t the only source of iridium.

Volcanoes produce it, too.

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 likethis:

produced immenselayers of basalt asthe Indian Plate passed over the Reunion hotspot.

And while the Deccan Traps were erupting,the eruption would have had effects something like this:

Over a million years, this might beexpected to have some effect onthe atmosphere.

Volcanic effects on the atmosphere & climate

Mount Pinatubo, 1991

Ash has an immediate effect;SO2 a longer-term effect.

Timing is everything.

Chicxulub is too early … by 300,000years or so.

There still is a K/T boundaryand 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 volcanicactivity.

The net result of thesefactors was a stressed,cooler climate for a million years, with ‘knockout’ blows at the end.

The DUST factorEven with elevated volcanic activity, and theoccasional asteroid impact, the atmosphereis resilient. Ash and aerosols get rained out andbecome 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.

Phytoplankton need iron to grow!

Experimentally-inducedphytoplankton bloomcreated by adding iron

Dust comes from dry land

(and also volcanic ash)

So cooler climate means more dust goes into theocean; phytoplankton growth increases; increasedocean primary productivity (photosynthesis) maintains lower atmospheric CO2 concentrations,

keeping the climate cool.

And thus:

+ +

=

Epilogue: Dust, CO2, and temperature

Iron in airborne dust acts as Earth’s ‘chemostat’ – keeping coolclimate conditions cool. Conversely, less iron means less productivity,allowing higher CO2 concentrations to persist.

The End