ESCI409 Spheres

Geologic history of Earth – 4.5bil years old – humans have barely been around for any of it  

  • Life started developing around 4000mil years ago, humans show up ~0.3 mil yrs ago 

Extinctions 

  • Permanent elimination of one (or more) species 

  • 99.9% of all species that have ever lived are now extinct 

  • Throughout geologic history, there is a steady ‘background’ rate of extinction due to the pressures of predation, competition, and environmental change 

  • There have also been mass extinction events, when multiple species have gone extinct at the same time 

  • Appear as abrupt disruptions 

  • Biggest known is the Great Dying – around 250mya 

Geologic time scale 

  • Precambrian lasted from 4600mya to 541 mya 

  • Paleozoic 541mya to 252mya 

  • Mesozoic 252mya to 66mya 

Great Dying 

  • Permian-Triassic extinction event 

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  • Largest mass extinction in Earth’s history 

  • ~252 million years ago 

  • Loss of ~75% of species, some estimates go as high as 96% of marine species 

  • Ecosystems required ~10mil years to recover pre-event diversity, and many families never came back 

  • End of trilobites, pareiasaurs, and gorgonopsians 

  • Golden spike in China, time period is visible 

  • Meishan Permian-Triassic GSSP dates ash beds around mass extinction 

  • Foraminifera 

  • Single-celled protozoa, most <0.5 mm 

  • Currently ~8,000 species 

  • Live in oceans, where they comprise >55% of Arctic biomass and >90% of deep-sea biomass 

  • Shapes have changed over geologic time 

  • Species distribution in Meishan Permian-Triassic GSSP shows mass extinction event 

  • Similar geologic evidence in the Dolomites 

  • Generally believed to have been caused by volcanic eruptions on Pangea that formed the Siberian traps 

  • 300,000 years before to 500,00 years before Permian-Triassic boundary 

  • Eruptions are believed to have kick-started a global warming 

  • Volcanic eruptions released carbon dioxide (potentially additional from burned coal deposits) and sulfur dioxide 

  • Greenhouse effect – carbon dioxide raised global temperaures 14-18 degrees F 

  • Warmer water can hold less dissolved oxygen (becomes anoxic) 

  • Carbon dioxide absorbed by the ocean, caused acidification 

  • Acid water toxic to many marine invertebrates 

  • Acidity changes precipitation of calcium carbonate minerals (calcite and aragonite), which form the exoskeletons of many marine invertebrates, including corals and mollusks 

  • Other possible impacts: 

  • Forests died (many in forest fires or due to acid rain), so runoff of sediment and nutrient increased 

  • Warming changed ocean circulation, which further reduced dissolved oxygen available to marine creatures (invertebrates and fishes) 

  • Nutrients and low oxygen led to microbial and algal blooms, which may have released dissolved and gaseous toxins 

  • Weather patterns shifted, causing wet regions to become dry and vice versa 

Extinction of the dinosaurs (K-Pg or K-T event) 

  • Killed off approx. 75% of plant and animal species, incl. All non-bird dinosaurs 

  • 66mil years ago 

  • Afterwards, surviving groups (mammals, avians, lizards) exhibited sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches 

  • Asteroid theory 

  • 1980 – Luis Alvarez and son Walter proposed that dinosaurs went extinct following impact of an asteroid 10-15km in diameter, created a 150km crater 

  • Locally, enormous shock wave, fires, earthquakes, winds, tsunamis 

  • Impact would have thrown trillions of tons of debris into the air – would have created months of darkness and cooled planet for months to years 

  • Evidence for asteroid theory 

  • Appropriately sized round depression identified in Mexico, which was later shown to have minerals  (shocked quartz), rock density (gravity anomaly), and ejectates (Tektites) expected from an impact source 

  • Marine sand deposits far inland, suggesting large tsunamis 

  • Layer of iridium, which is more common in meteorites than on earth, found globally; no dinosaur fossils above 

  • Species that depended on photosynthesis preferentially went extinct 

  • Other additional/competing causes 

  • Deccan Traps flood basalts in India created during 2mil years before extinction, continuing to boundary 

  • Could have caused global cooling (sulfur dioxide and dust) and/or warming (carbon dioxide) 

  • Could have destabilized ecosystems prior to asteroid impact 

  • Additional asteroid impacts dated to same period, perhaps from fragmented asteroid 

  • Sea level drops 

Global cooling 

  • Particles from volcanoes, sea salt, pollution, etc. Can nucleate clouds 

  • Unlike gases, clouds reflect sunlight back out to space 

  • For example, ash and sulfur dioxide from volcanic eruptions can lead to temporary global cooling once it mixes throughout troposphere (lower atmosphere) 

  • Modern examples 

  • Mt. Pinatubo (June 1991)  

  • Mt. Tambora (1815) - The Year Without A Summer – temps 0.4 - 0.7 degrees celsius below normal, massive food shortages 

  • Other similar events: Hekla 3 (1200 BC), Hatepe (AD 180), Laki (1783-84), Krakatoa (1883) 

  • Modern effect of volcanoes on climate 

  • Temporary short-term cooling following major explosive eruption 

  • Negligible impact on greenhouse gas emissions/global warming 

  • 1% of what human activities produce for CO2 yearly 

  • Asteroid impacts: NASA does have a planetary defense coordination 

New England Tectonic History 

  • Slides I am not writing this down 

Earth cycle 

  • Everything is connected 

  • Habitable part of Earth is a very very thin layer 

Ocean 

  • Much deeper than continental crust 

  • Water is stratified based on density (warm less dense than cold, fresh less dense than salty) 

  • Thermohaline ocean circulation – cold/warm water leading currents 

  • Density-driven circulation near river mouths 

Atmosphere 

  • Troposhere – lowest, to 10km 

  • Stratosphere – 10km to 50km 

  • Mesosphere – 50km+