Earth Sciences 240A;: Lecture 8

PART C: Mass Extinctions and the Impact Connection: Introduction

Extinctions

Background

Average species lifespan: 4 million years

99.9% all species gone

Records

Sedimentary rock layers

Mass extinctions

>30% species World-wide

Different ecologies Short time

Single or clustered causes

(~4x background min.)

The Impact Hazard

Impact flux (poor statistics): Total mass [10⁷ – 10⁹] kg/year

1 mm: ~ every 30 s

1 km: ~ every 1 my

10 km: ~ every 100 my

Impact Tsunami

Power factors: land: 1/3; seas: ½

Catastrophic threshold

Death of >25% population (1.75 b people)

Asteroid 3 g/cm3; 20 km/s; 1.7 km diam.

Kill Curves (Ref. Raup 1990)

Craters larger than 70 km; very few with good statistics

~ Agreement with predicted curve

Conclusion:

“for craters smaller than 50 to 60 km diameter, there should be no associated extinction above threshold level”

Computer Simulations

Scale problem for lab experiments!

Computer models (Russian study):

(1) 10 km asteroid; v= 20km/s; ignore gravity; 5km deep ocean target

Produced all the features for a K-T event

(2) Same as first but add atmosphere

Atmospheric shock wave; insignificantly smaller seismic shock than first

Conclusion: predictions OK

Regional/Global Effects

Massive earthquakes

Solar-b locking atmospheric dust

Widespread wildfires (added smoke)

Into sea: water vapour + CO2

Into sea: gigantic tsunami

Acidic rains

Next

Extinctions through time