Lecture 8

Debate 1: What Killed the Dinosaurs? (cont.)

Volcano-Greenhouse Theory

What is it?

• volcanism from Deccan Traps in India

  The Deccan Traps are one of the largest volcanic provinces in the world, consisting of more than 6,500 feet (> 2,000 m) of flat-lying basalt lava flows and covering an area of nearly 200,000 square miles (500,000 square km) (roughly the size of the states of Washington and Oregon combined) in west-central India.

  • Deccan (region of India) Traps (means staircase) produced over 500,000 years, as Indian subcontinent drifted north to collide with Asia

  • hot spots and mantle plumes lie under continents, resulting in huge, lasting flows, sometimes producing explosive events and calderas like Yellowstone National Park, Kilauea in Hawaii, and Iceland

    

    

  • about 65 million years ago, Traps lavas erupted (movie)

  • flooded over a million square miles of India with basaltic lava flows (volcanic igneous rock low in silica (40-50%) and high in Fe and Mg that is produced by partial melting of mantle and forms bulk of oceanic crust)

    Example of basaltic lava flow in Hawaii

  • after all this time, still 1 1/2 miles thick in western India, near Bombay

  To read more about determining the age of the Traps and how they formed, click here.

• injection of ash, aerosols (containing sulphur), and gases into atmosphere, the increased atmospheric sulphur can lead to more sunlight being reflected, a colder earth results...

  

• climatic disturbances lasting tens or hundreds of thousands of years
  • over short term, volcanic eruptions lead to terrible (even ``nuclear'') winter and acid rain

  • oceans could not dissolve CO₂ --> filled atmosphere, surface waters

  • reduced photosynthesis, killing oceans, and forming K-T boundary clay layer

  • acidity and composition of surface waters killed single-celled algae --> doubling CO₂ content of atmosphere

  • up to factor of 5 increase in atmospheric CO₂ --> carbon cycle perturbation, greenhouse effect, temperature increase

    Others suggest a resulting temperature change as large as 10 degrees C.

• conduit to transport iridium to Earth's surface?
  • estimated total quantity of iridium deposited (200,000 to 300,000 metric tons) is difficult to explain, BUT

  • iridium concentrations at K-T boundary vary widely (from 0.1 to 100 parts-per-billion) and concentrations of one to several parts-per-billion found in rocks of terrestrial origin --> what exactly is meaning of ``iridium anomaly''?

  • maximum iridium found in coal vein, and marshy environment that favors coal deposition can also concentrate metals like iridium

  • volcanism is better at producing observed levels of arsenic, antimony, selenium, which are relatively scarce in meteorites

• volcanism could be responsible for K-T boundary layer
  • while clay at K-T boundary often interpreted as altered dust deposited rapidly all over globe after impact, clay is not present everywhere

  • clay of similar chemical composition found several meters above and below boundary

  • presence of feldspar, labradorite also suggest alteration of basaltic, volcanic ash

• in general, association among birth of hot spot, formation of basaltic traps, mass extinction, continental break-up, and birth of ocean

  • Moreover, there is evidence that massive volcanism led to a run-away green-house (+100 C) that removed water (and possibility of life?) from Venus (and maybe Mars).

  • Permian-Triassic mass extinction of 250 million years ago, greatest in Earth's history, coincided with Siberian Traps volcanism, one of greatest episodes of flood basalt volcanism in history. There have been many mass extinctions in the Earth's history.

    

  • seven of ten principal extinctions (including two worst) can be associated with episode of massive basaltic volcanism

    

• perhaps on single, K-T occasion, while Deccan Traps erupting and biosphere already stressed, impact happened

• iridium rich layer sandwiched between two flows from Deccan Traps

Major weaknesses of volcano-greenhouse theory is that iridium anomaly and shocked quartz at K-T boundary not yet explained.

To read some more about the dinos, check out the Hand-Outs and Reference Materials page.

To read some more about mass extinctions, the asteroid impact theory, and alternative theories, click here, here or here.

To read more about current issues and controversies in the field of dino death, click here.

If you want to see how nasty the fighting over this topic can get, click here.