Earth Sciences 240A: Lecture 9:  A trip through time

 

Proterozoic Life

Until ~2.0 bya all life anerobic

First photosynthetic organisms; Huge extinction

Development of eukaryotes at 1.8 bya

First atmospheric ozone

~700 mya: first metazoa

Proterozoic Tectonics

Rodinia: first supercontinent; Vendian time (before Cambrian)

Snowball Earth: huge extinction

Gradual breakup as Cambrian began

Many new niches for life (explosion of life)

Paleozoic Era Tectonics

Rodinia fragmentation throughout Cambrian; ended by Mid – Ordovician

Pangaea assembly

First hints of assembly: Late Ordovician

Plate collision: mountain belt construction

Laurasia; Gondwana; (China)

Permian: fully assembled; redbeds

Paleozoic Era Life

Early stages: Atmosphere: more O2; less CO2; Ozone shield

First land plants: 470-440 mya

First land animals: 440 mya

Ordovician-Silurian Event: 439 mya

Large post-PC extinctions (est. 70%)

No unusual tectonic activity, but terrible rock records

Apparent 2-stages of Ir enrichment

China: small Ir peak

Yukon: no Ir, but other ‘asteroid elements’

Quebec: v. weak Ir peak

Scotland: v. weak Ir peak

No tektites, shocked minerals, soot, etc.

Strong glaciation evidence??

Devonian Event: 367 mya

Multiple weak Ir peaks; Micro-tektites

6 craters correct age; all too small?

Abrupt fossil changes

Debris flows/chaotic deposits (tsunami?)

Same isotopic changes as at K-T

Conclusion: Significant extraterrestrial event

Possible weak glaciation??

Carboniferous to Permian Life

Amphibians became abundant; Reptiles (amniotic egg)

Initial inland seas rich in life and Initial luxurious forests

Late Permian:

Interiors dried up; Abundant redbeds (shallow inland seas); Interior deserts

Background extinction high

End-Permian Event: 245 mya [The Mother of all Extinctions]

96% loss of marine/terrestrial species; Global extent

Gradualists:

high stress over long time

Siberian Traps (huge volcanic eruptions)

Catastrophists:

China section: est. 10,000 year max.

C, Ir, O isotopes consistent with impact

Some tektites

Support: Alps, Austria, Italy, India

No obvious crater large enough

Mesozoic Era

Pangaea fragmentation begins

Age of reptiles; Dinosaurs dominated every environment

Mammals started; tough life

Triassic-Jurassic Event; 208 mya

No abnormal tectonics

At least 3 weak Ir-rich boundaries

Shocked quartz

C and O isotopes look same as Late Devonian event

Likely multiple impacts, but not well studied

 

Next

The K-T Event

 

Remember:

13 October: Thanksgiving Holiday

15 October: Mid-Term Test (001 students only)