Avalanches None of this whatsoever has been proven

Avalanches…. None of this whatsoever has been proven. But that’s what fun about it

…at the CMB CORE MANTLE

Richard. A. Muller- hero. http: //muller. lbl. gov/ Avalanches at the Core-Mantle Boundary, Geophysical Research Letters, vol 29 pp 41 -1 to 41 -4 (2002)

Earth Structure- the CMB and D’’

How will they FORM I hear you say? Please don’t let Charlie bite my finger…

Let it snow, let it snow… � 70% of density change as liquid core solidifies is due to exclusion of lighter element exclusionleads to convection. � Excluded light elements remain in solution and freeze out as they rise (1000 o. C temp drop I. C to CMB) � Light elements fall like snow onto undulating surface of CMB � Gathers like snow…how nice… � Exceeding the angle of repose will cause slumping, bringing core liquid with it. � Only need a few degrees slope. � Shear stress causes slumping- oblique impact?

Meteor Impact � Must be oblique � Consider, for example, a comet with velocity 25 km/sec, radius 5 km � ΔΩ � If = mv. R/I the magnetic field of the core is coupled to entrained Fe in the sediment, sudden acceleration could cause an avalanche.

What would they DO I hear you say?

Consequence numero uno � Trigger the disturbance of the geodynamo ◦ Implications for magnetic reversals

Geodynamo � Slumping Heat re-distribution as cool precipitate mixes with hot liquid Fe, cooling the Fe and letting it fall due to density increase. � This may disturb large convection cells of the outer core, reduce the overall scale of flow and even change the dipole component. � Cells in close association may be also affected, driving an overall shut down of the geodynamo

Geodynamo cont… � When the convective cells re-establish themselves, there is a 50% chance the magnetic field will reform in the reversed direction. Help. I have absolutely no idea where the hell I am I’m lost too mate…must be the geodynamo again. Game of chess?

Consequence numero dos � Mantle Plume initiation ◦ The part of the mantle that lost the ‘sediment’ blanket is exposed to hot Fe and rapidly heated �Maybe only from the largest of avalanches (thickness >>100 m)

Consequence numero dos Mantle plume initiation �Flood Basalts and Kimberlites

Mantle plume initiation �Flood Basalts and Kimberlites If several avalanches are coupled from an intense impact, could result in separate but simultaneous plumes e. g simultaneous but spatially distant plumes at 61 -62 Ma (Larson et al. 1999)

A grand unified theory- MASS EXTINCTIONS � Meteor impacts and flood basalts have long been possible explanations for mass extinctions. � Flood basalts almost always seem to postdate the main phase of extinction � This would be satisfied by the impact avalanche model TIME? ? ? Mantle plumes take millions of years to reach the surface- would destroy correlations. Kimberlite rates- 300 km/s?

Evidence for linking reversals to impacts � Reversal in fall back breccia of 24 -km Reis impact crater. � No reversal occurs with Chicxulub crater ◦ Oooooo…. . ◦ High iridium suggests impact was vertical (would have been ejected to space if oblique)? ?

Geomagnetic quiet periods � 120 -85 Ma has no magnetic reversals � Linked to mantle plume activity (Larson and Olsen 1991) which created Ontong-Java plateau � The LARGEST, yes, the largest, volcanic province on Earth. Alaska, 30 Km thick.