Set 4: The Alvarez Hypothesis

Iridium

Platinum group metal

Foram

Iridium anomaly

Aristarchus

Heliocentric in 3rd century BC

Alfred Wegener

Continental drift

Gregor Mendel

Genetics

Shatter cones

Fossil shock waves, horsehair texture

Shocked quartz

>= 2 sets parallel deformation features, only at craters and nuclear sites

Spherules

Tiny 'glass raindrops' that turn to clay

Tektites

Large, teardrop shaped 'glass raindrops'

Chelyabinsk

Siberia 2013, dust plume wrapped the Earth

Tunguska

Siberia 1908, flattened forests

TC3

Tracked from sky to ground in Sudan

Coesite and stishovite

High pressure forms of quartz found at impact sites

Walter's question

How much time in K-T boundary clay

Discovered K-T shocked quartz

Bruce Bohor

Earth's iridium

Mostly in the core

Luis Alvarez

Physicist

About 10 km diameter

The K-T asteroid

Proposed killing mechanism

Dust blocks the sun and photosynthesis

Alvarez Hypothesis, Part 1

Bolide impact occurred precisely at the K-T.

Alvarez Hypothesis, Part 2

The impact caused the K-T extinctions.

1980

Alvarez Hypothesis published in Science

Formed by impact

The Moon

Meteor Crater, Arizona

Gene Shoemaker's starting point

World's only globally distributed rock layer from a single event

The K-T boundary layer

Global iridium anomalies

Volcanic "spherules"

angular, not rounded

Volcanic iridium

from non-explosive (basaltic) volcanoes

Deccan Traps

Massive lava flows from India

Peak of Deccan eruptions

Hundreds of thousands of years before and after the K-T

Major effect of Deccan eruptions

Short global warming episodes, biodiversity increased

Granite and quartz

K-T impactor struck a continent

Double boundary layer

North America only

Lead of Chicxulub discovery team

Alan Hildebrand

First noted Chicxulub gravity and magnetic anomalies

Penfield and Camargo (1981)

Global, regional, and local events revealed in one place

West Bijou Creek K-T section

Chicxulub gravity field

Cenotes

Chixculub ring from space shuttle

Same isotopes, 3 different elements

Impact glass in Haiti and Chicxulub

Same age within 32,000 years

Chicxulub and North Dakota K-T ashes

Same lead loss line and age

Zircons from Chicxulub and N America K-T boundary

Signor-Lipps effect

Observed extinction may precede true extinction

Least Signor-Lipps effect

Superabundant microfossils, forams and pollen

Most Signor-Lipps effect

Rare, large fossils (dinosaurs)

Overcome Signor-Lipps effect

Heavy sampling and statistics

The key question for Part 2 of Alvarez Hypothesis

Sudden or gradual extinction

Blake Nose, Florida

Complete K-T boundary, abrupt foram extinction

Cretaceous forams

Post K-T forams

60%

North Dakota plant extinction

K-T plants with confidence intervals

No survival known

Cretaceous leaf miners

How to study insect diversity and extinction without insect fossils?

Insect feeding marks on fossil leaves

Second reason insects died

Host plants went extinct

Only detailed record of the end of the Mesozoic on land

Hell Creek Formation

Quantified global dinosaur diversity and sampling

David Fastovsky

Dinosaur diversity and sampling, whole Mesozoic

Dinosaur diversity and sampling, last ~35 my of Cretaceous

Dinosaur diversity, last ~19 my of Cretaceous

Quantified vertebrate diversity in Hell Creek Formation from 10,000 fossils

Dean Pearson

Vertebrate diversity, last 0.7 my of Cretaceous

No Bone Zone

Youngest dinosaur known

Evidence we have seen for pre K-T decline or gradual extinction of any group

0

Number of mass extinctions currently attributable to impacts

1

Fossil vs. modern extinction rates

Where extinction risk is increasing

Climate change impact scenarios

Shoemaker data

Shoemaker-Levy 9