L19 Mass extinction

Earth’s sixth mass extinction event

About 200 years ago there were nearly 30 million bison roaming planet earth.

1890

As few as 750 bison were left in North America due to extreme overhunting

Next great extinction: Climate change (Human activity indirect action)

2004

Climate change could drive million of the world’s species to extinction as soon as 2050, scientific studies says.

2023

Agriculture accounts of all land 40%

Global deforestation of globe 90%
Fresh water use 70%

Greenhouse emissions and global warming, frequent intense droughts, storms and floods

Linked greenhouse gases in Ireland are fossil fuels 62% and agriculture 38&.

These factors significantly alters habitats, leading species to extinction and loss of habitat and ecosystems worldwide.

What could the 6th mass extinction be?

Asteroids

Global nuclear war

Global warming

Eruption of super volcanoes

Geo-engineering disaster

Genetically engineered killer microbe

Artificial intelligence?

Mass extinctions major inter minor diagram

The K-T event

Key points to the catastrophic, extra-terrestrial cause of K-T event

• external to Earth system

• no reason to assume biotic stress in Earth system in advance of impact

• sudden event

• global effect from local source (impact): what is the killing mechanism

Summary of the K-T event

Evidence of the impact of the K-T event

Iridium (Ir) anomaly

• low abundance on Earth (core) but abundant in meteorites supplied continuously to Earth from space.

• Accumulates sedimentary record in extremely low abundances

• Anomaly refers to elevated abundances found in K-T boundary sections.

Iridium Anomalies map

K-T boundary clay layer in Contessa (Italian Appenines)

Boundary clay

Thin (in cms or less), fine-grained layer (clay & coal)

global distribution

usually distinct from lithologies above and below

hosts other evidence (Ir anomaly, tektites, Impact glass etc)

Tsunami deposits

rapid (geologically instantaneous) deposition of sediments can occur after events such as earth quakes HOWEVER

tsunami deposits at K-T boundary concentrated in Caribbean region

Tektites

natural glass → microscopic in size

shapes often, suggesting rapid cooling while moving

low water content; can include partially melted zircons

suggests formation of very high P + T

Impact glass

Rapid quenching of molten droplets

Found at the base of the K-T boundary sequence in the Gulf of Mexico region

Shocked quartz

unusual microstructure

cross-cutting shock lamellae

deformation of crystal structure

Stishovite

High temperature of polymorph of quartz

The ‘fern spike’

short-lived high increase in abundance of fern spores at K-T boundary

ferns adapted to low-light conditions

The Chicxulub crater aka ‘the smoking gun’

impactor estimated at 10km diameter, crater radius up to 80km.

Cores from crater reveal unusual lithologies

Suevite (suevite breccia)

Chicxulub melt rock from well Yucatan 6

melting and solidification in situ (‘in place’)

formed and deposited relatively close to impact crater

Crater morphology

Combination of melt rock and suevite (breccia) within and adjacent to impact crater

Mass wasting deposits → i.e. landslides

mainly in Caribbean and easter seaboard of South and North America.

Summary of evidence from impact away from crater

The K-T event: Could impact cause the mass extinction?

Evidence doesn’t prove it resulted in extinction

Although demonstrates the cause and effect (killing mechanisms)

Indirect killing mechanisms

Plausible result from asteroid impact

• sever reductions of light levels

• changes of temperature

• acid rain

• wildfires

Lots of combos