A Guide to the Big 5

deccan traps- aikavaellus.fi
Artist rendition of The Deccan Traps erupting. Image Courtesy of aikavaellus.fi

Perhaps you’ve heard about the asteroid impact that wiped out the dinosaurs, but did you know there have been five mass extinction events throughout earth’s history? These events have dramatically altered the proliferation of life on the planet and helped spur on the rise of mankind. Here’s a quick guide the big 5.

ORDOVICIAN- SILURIAN 454 MILLION YEARS AGO

ordivician silurian mass extinction
Orthocones, the triangular shaped cephalapods, swim alongside trilobites, crinoids and other Ordovician marine life. Image Courtesy of Masato Hattori

Suspects: Ice Sheets or Large Igneous Provence (LIP) eruption

Victims: 85% of Marine Sea Life: trilobites, brachiopods, graptolites

The Ordovician-Silurian mass extinction was the first of its kind and wiped out much of early life. Scientists believe that it may have been caused by a series of long- winded volcanic eruptions(1). In earth science, chains of volcanoes are often referred to as Large Igneous Provences or LIP’s. They are probable suspects for 4 out of 5 mass extinctions on earth. According to a model made by Lefebvre et al, a team of earth scientists at the University of Lille, the right parameters could’ve set off a mass extinction. But what kind of parameters could annihilate 85% of life?

  1st The basaltic eruption would have been large. Lefebvre and team estimate that in order for the volcanoes to inflict global damage a magnitude of 2.5×10^6 sq km is expected. That’s about the size of  Texas and Alaska combined.

2nd  In addition to sheer size, the traps would need to erupt for an extended amount of time. The model predicts that a weary 600,000 years of continuous eruption would release enough CO2 to dramatically acidify the world’s oceans.

3rd Additionally, the traps would have needed to be centered along an equatorial latitude to effectively spew their magmatic contents worldwide.

If these checks were marked, the eruption would not only heat up the world’s oceans but also simultaneously warm the world’s atmosphere (1). In the aftermath, once all the erupted basaltic lava flows cooled, a mass weathering event of the new material would have induced a global cooling event. Evidence of increased basaltic weathering in the rock record lends credence to this hypothesis.

LATE DEVONIAN 375 MILLION YEARS AGO

late devonian
One of the biggest losses was the tank size armoured fish Dunkleosteus. image courtesy of University of Texas Austin

Suspects: LIP eruption, Anoxic Seas, Asteroid impact, Proliferation of Plants

Victims: 75% of all species on earth. Particularly coral reefs, fish, and Dunkleosteus all perished.

Similarly, the Late Devonian extinction which occurred between the Frasnian and Famennian periods, may have been caused by another LIP, specifically, the Viluvy Traps in eastern Siberia(3). Since the traps likely erupted over a period of 100,000 years, they could explain the 5 distinct pulses of extinction noted during this time (i.e. the pulses correlate with times of high volcanic activity from the traps)(4).

On the other hand, during the late Devonian, deep-rooted vascular plants were coming on the evolutionary scene. Some scientists think that the first land plants would have caused dramatic weathering, and washed organic material into the oceans (4). As a result, increases in macronutrients and organic content triggered  eutrophication events that resulted in anoxic (oxygen poor) seas. While evidence for anoxic waters can be seen in the dark-colored Kellswasser shales of the period, this argument does not account for the mass extinctions of land species (4). This is why many consider the Viluvy LIP eruptions to be a better explanation.

PERMIAN- TRIASSIC 252 Million Years Ago

Permian Seas - National geographic
Image Courtesy of National Geographic

Suspects: The Siberian Trap LIP eruption

Victims: 94% of marine life including crinoids ( similar to starfish on a stick),  Diictodon ( a puppy size dinosaur) , and lystrosaurus (similar to an overweight komodo dragon).

The Permian-Triassic mass extinction was the most catastrophic of the big 5 extinctions. Estimates show that nearly 94% of all marine species went extinct because the oceans became an acidified dead zone. Here’s one explanation.

During this extinction, the Siberian Traps covered 720,000 sq. miles of land along what is now modern day Siberia. That’s equivalent to the entire state of California being covered in volcanic chains. The traps erupted for a period of ~500,000 years (5) and spewed over 3,000,000 sq. miles of basaltic lava flows (5). As a result, they released billions of tons of SO2 that not only would have produced sulphuric acid rain that would have decimated plants and triggered a volcanic winter, but also would have reflected enough sunlight to cause a subsequent cooling event. Evidence for this is found in the increased amount of CO2 in plant spores from Greenland fossils dating back to the time of extinction (5). These plants show mutated spores that have fewer stomata, a result of chronically high CO2 levels (5).

Another point of evidence is the high amount of Hydrogen Sulphide found in Permian-Triassic rocks. In marine environments, hydrogen sulphide is a byproduct of opportunist bacteria that thrive in anoxic water. Increased HS suggests that the oceans were too oxygen-poor for life.

Lastly, increased warming from CO2 may have led to the thawing of methane hydrates frozen at the bottom of the ocean. Once thawed, these hydrates would have released tons of methane, a greenhouse gas 30 times as potent as CO2, into the water and atmosphere. This would have caused an extreme warming event. In total, these quick, dramatic changes in climate would have decimated life on land and especially in the Permian seas(5).

TRIASSIC- JURASSIC 201 MILLION YEARS AGO

Triassic- Scientific American Blog
Image Courtesy of Scientific American Blog

Suspects: LIP eruption or Climate Change

Victims: 76% of species including marine reptiles, crocodylomorphs, and pterosaurs

Another notable LIP eruption may have happened at the Triassic-Jurassic boundary. During this extinction, nearly 76% of species went extinct including some of the most iconic marine reptiles like mosasaurs (see Jurassic World ending), plesiosaurs (see The Loch Ness monster), and ichthyosaurs. A notable drop in ammonoids, conodonts, archosaurs, and other marine reptiles in the fossil record point to LIP eruptions and massive sea level changes as potential culprits (2).  Similar to the Ordovician-Silurian LIP scenario, the eruptions would have dramatically increased CO2 and SO2 in earth’s atmosphere. As a consequence, the Earth’s oceans and rain would have been acidified. 

K-PG 65 MILLION YEARS AGO

kp-g extinction- Thoughtco
image courtesy of Thoughtco

Suspects: Asteroid, or LIP eruption

Victims: 75% of life including Deinonychus, Velociraptor, T- Rex, and all dinosaurs except birds

The most famous and fantastical K-Pg extinction occurred 65mya during the Cretaceous period. It was most likely the result of a large asteroid impact. Although some scientists suggests that an LIP eruption is to blame, the majority of evidence indicates that an asteroid impact imploded enough debris to cover the earth and cause a nuclear winter. Evidence for this can be seen in the very abrupt change in the rock record from sedimentary to fine clay (7). Furthermore, iridium, an element found in space but not naturally on earth, is deposited along boundary worldwide (7). This suggests that the Iridium was brought to earth  on the back of an asteroids. Moreover, the presence of shocked quartz, a form of quartz only created from extremely high pressure and temperature conditions, was found around the K-PG boundary worldwide(7). A large asteroid impact could have generated enough heat and pressure to create the conditions needed for shocked quartz. Most importantly, the crater itself can be seen in the Chicxulub ring of Yucatan, Mexico, where the deposits date back to the time of the extinction (7). In total, the impacts of this asteroid would have obliterated most dinosaur species, but allowed for burrowing mammals, and birds to persist.

A 6TH EXTINCTION?

image courtesy of Fstoppers
image courtesy of Fstoppers

As signified earlier, many of these events were the result of massive amounts of CO2 being released into the atmosphere. This disrupted weather patterns, caused droughts, increased ocean acidity, and released methane hydrates. While these mass extinctions could be attributed to natural stochastic events like LIP eruptions, or weathering continents, the rate of carbon currently being released into the atmosphere is outpacing the magnitude of some of the most dramatic LIP trap eruptions.

Equally important, a mass extinction is characterised by a species going extinct quicker than its normal background extinction rate. Presently, amphibians are going extinct at a rate 25,035  times faster than their natural background extinction rate (9). This is alarming because amphibians are the “canary in the coal mine” for climatic disaster. This is because their highly sensitive skin is the first to react to changes in the environment. Likewise, birds have also experienced dramatic declines at a rate of ~12 species per year (10). Current estimates suggest that extinction rates for all species are 1000-10,000 times faster than their background extinction rates (11).

Current signs paint a grim picture of a society on the precipice of a mass extinction. If business continues as usual, then the first anthropogenic mass extinction could be recorded in the rock record. However, if greenhouse emissions cease, and efforts are taken globally to mitigate human effects on the environment we could allow the earth time to recover and reset. But if not… we’ll have to hold our breath, cross our fingers, and hope that our furry burrowing friends can pass on life after we’re gone.

What do you think? Let me know in the comments!

-Tori

Sources:

  1. Lefebvre, V., Servais, T., François, L. & Averbuch, O. Did a Katian large igneous province trigger the Late Ordovician glaciation?: A hypothesis tested with a carbon cycle model. Palaeogeogr. Palaeoclimatol. Palaeoecol.296, 310–319 (2010).
  2. WAYS TO DESTROY LIFE. Available at: http://palaeo.gly.bris.ac.uk/palaeofiles/triassic/exttheory.htm. (Accessed: 10th November 2017)
  3. Stigall, A. L. Speciation collapse and invasive species dynamics during the Late Devonian “Mass Extinction”. GSA Today22, 4–9 (2012).
  4. a0001653.pdf. Google Docs Available at: https://drive.google.com/file/d/0B_iBV1KRAnqDWTUtWU1pakt6YjQ/view?usp=embed_facebook. (Accessed: 10th November 2017)
  5. Space And Intelligence. Snowball Earth/ the Permian Extinction.
  6. Lenton, T. M., Crouch, M., Johnson, M., Pires, N. & Dolan, L. First plants cooled the Ordovician. Nat. Geosci.5, 86–89 (2012).
  7. K-T Event. Available at: https://www2.jpl.nasa.gov/sl9/back3.html. (Accessed: 10th November 2017)
  8. The Ediacaran Period. Available at: http://www.ucmp.berkeley.edu/vendian/ediacaran.php. (Accessed: 10th November 2017)
  9. background extinction rate for amphibians – Google Search. Available at: https://www.google.com/search?q=background+extinction+rate+for+amphibians&oq=background+extinction+rate&aqs=chrome.0.69i59j69i57j0l4.5860j0j7&sourceid=chrome&ie=UTF-8. (Accessed: 10th November 2017)
  10. background extinction rate for birds – Google Search. Available at: https://www.google.com/search?safe=active&ei=5TwFWoLRJoWDmQHs0p24DA&q=background+extinction+rate+for+birds&oq=background+extinction+rate+for+birds&gs_l=psy-ab.3..33i22i29i30k1.3062.5907.0.5977.11.8.0.0.0.0.478.1675.2j2j0j1j2.7.0….0…1.1.64.psy-ab..4.6.1542…33i160k1j0i22i30k1.0.lkP8Bk-7-F4. (Accessed: 10th November 2017)
  11. current extinction rate – Google Search. Available at: https://www.google.com/search?q=current+extinction+rate&oq=curr&aqs=chrome.0.69i59j69i57j0j69i60j0l2.1679j0j7&sourceid=chrome&ie=UTF-8. (Accessed: 10th November 2017)
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