Did you know that 98% of recorded life that has ever existed on the Earth is now extinct?  I did!  Well, I only just learned that fact, but what a huge number to wrap your mind around.  So in honor of this bizarro fact I’ve decided to devote a little time to E.L.E’s or Extinction Level Events.  There have been 5 that we know of.  I’ll break each one down (chronologically) and give you some of the more interesting facts and debates raging over these events.



Ordovician-Silurian Event

  • 450 Million Years Ago
  • Considered to be the second largest of the recorded events.  It’s also the earliest example we have on an Extinction Event.
  • 60% of Marine invertebrates died during this massive event.  Since most life was confined to the seas at this time, that’s a substantial impact!
  • At the time, there was a massive chunk of land most people refer to as Pangaea, however the southern region known as Gondwana was most affected as it was shifted to the south polar region.
  • The possible causes include:
    1. The unlikely Gamma Ray Burst.  Apparently a few research scientists believe that a star went Supernova some 6,000 light years away from Earth inside our Milky Way Galaxy .  The theory states that the very dangerous Gamma Ray Burst would strip a large portion of the atmosphere from the Earth within a matter of seconds, and instantly vaporize anything in its path.  Since there is no geological evidence, this theory is not accepted by many scientists.
    2. The second and far more accepted theory is an increase in volcanic activity and weather patterns.  Apparently there was an upswing in the level of CO2 (Carbon Dioxide) that in larger quantities is deadly to oxygen breathing animals.  This was an issue the astronauts of Apollo 13 had to deal with when their CO2 scrubbers were being overtaxed in the early 1970’s.

Late Devonian Event

  • 374 Million Years Ago
  • By the time of this event, or series of events as it has been theorized, plants and insects had moved to the land portions of the Earth.
  • Some scientists have gone so far as to suggest that there are 7 different extinction events during this time period!
  • In spite of the fact that there were land dwelling organisms, this event only seemed to effect marine life.
  • The numerous possible causes include:
    1. An Anoxic Event: This is the complete depletion of oxygen from the oceans, in particular the bottom oceans.
    2. An impact event known as the Alamo or Woodleigh impacts.  Evidence for this is scarce as dating has been inconclusive.
    3. Plant evolution.  Plant life evolved from a height of 30cm to nearly 30m.  This extreme growth may have caused bizarre weather patterns.  It may have also dangerously decreased CO2 levels.  Since CO2 is a greenhouse gas, a reduction of it would possibly lead to a colder climate.

Permian-Triassic Event

  • 252 Million Years Ago
  • Referred to as The Great Dying.
  • The largest recorded extinction event.  This saw 96% of all marine life and 70% of terrestrial or land life wiped from existence.
  • The rebuilding of life after this event took considerably longer than other events.  That’s why this has been referenced as “The mother of mass extinctions!
  • Finding the event that caused this, or earlier E.L.E.’s is difficult as the Earth is a very active place.  The seafloor is “recycled” every 200 million years due to plate tectonics, and all evidence of such events is nearly erased from existence.
  • The possible causes include:
    1. A massive impact event.
    2. A massive volcano or series of volcanic eruptions that caused complete coverage of the Earth in ash clouds.
    3. Something called Methane Hydrate Gasification.  I’m not entirely sure what it means, but evidence has been shown of a swift decrease in Carbon isotopes.  From what I understand, this could cause either hyperoxia (high-oxygen) or anoxia (low-oxygen) in the seas.  Since the ocean is a finely balanced ecosystem, anything that deviates from the norm can be devastating.
    4. Some research has shown evidence that it was a combination of events that caused such catastrophic extinction.

Triassic-Jurassic Event

  • 199.6 Million Years Ago
  • 20% of marine life was killed and at least half of life on Earth at the time (that we know of) was wiped out.
  • This event allowed the dinosaurs to rise up and become the dominant species on Earth during the famed Jurassic Period.
  • It was also at this time that Pangaea began to break apart.
  • The possible causes include:
    1. Asteroid impact.  Though the evidence has not been found, including the elusive impact crater of substantial size.  Those impact craters that have been suggested as the evidence have been shown to be too small.
    2. The least likely explanation is gradual climate change or sea-fluctuation.  Because of the suddenness of the E.L.E., this idea doesn’t really fit.
    3. Massive volcanic activity.  A release of either CO2, Sulfur Dioxide (SO2), or aerosols into the atmosphere would cause the climate to shift up or down.  Both are tragic to living organisms.

Cretaceous-Paleogene Event

  • 65.5 Million Years Ago
  • The most popular of the extinction events, it is often referred to as the K-T Extinction Event.
  • This was the event that saw the destruction of the dinosaurs and gave way to hominid species of which humans are a part.
  • Numerous marine and terrestrial life was wiped out during this event.
  • Evidence of this event is abundant, both geologically and paleontologically.  Fossil records of numerous species exists, most famously being that of the dinosaurs, which millions of people go to the museum every year to view.
  • The possible causes include:
    1. Numerous impact events, the most famous of these is the recently discovered Chicxulub Crater on the Yucatan Penisula in Central America.  The crater is one of the largest craters ever discovered.
    2. Sea-level regression.  There is evidence that the sea-level dropped considerably at this time.  Why the seas regressed is still a mystery.
    3. A combination of things could have lead to this mass extinction.
While it is interesting to study and see what has happened before in our planet’s history, it is also very humbling.  Our planet has existed for a very long 4.54 billions years.  Our recorded history goes back to the 4th millennium BC with the invention of writing.  We have existed for a fair bit longer than that, but in the grand scheme of the Earth, or the Universe for that matter, we are a tiny drop in the bucket.  To see just what I’m talking about, look up Carl Sagan’s ideas with his Cosmic Calendar.  An example of the calendar has been added below for your convenience.
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Boom goes the Earth!

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