Mass Extinction Theories

• Theories of Mass Extinction

Glossary

• Extinction refers to the complete disappearance of all living individuals of a particular type, no longer existing anywhere on Earth.
• Background Extinctions are the normal, continuous rate at which species disappear.
• Mass Extinctions are periods in Earth's history when a significant portion of life dies out, causing biodiversity to collapse.

Why Extinctions Occur

• Environmental disasters, such as meteor impacts can be a cause.
• Failure to adapt to sudden environmental changes such as ice ages where ectotherms are unable to cope to declining temperatures.

Geologic Time Scale and Mass Extinction

• In each mass extinction event, 70-90% of all life on Earth can be eliminated.

Layers of the Earth Explained

• Crust: The outermost layer of Earth, composed of solid rock and minerals, broken into tectonic plates that can shift. Parts of the crust are covered by water
• Mantle: A very hot, semi-solid rock layer that moves slowly, causing the tectonic plates to shift above it.
• Core: Consists of an outer core made of melted metals and an inner core, which is a solid ball of iron and nickel.

Two Ways Mass Extinctions Can Occur

Intrinsic Factors (Terrestrial/Earthly)

• Plate Tectonics: Movements of the Earth's crust.
• Continental Drift: The gradual shifting of continents over time.
• Changes in Climate: Heating and cooling patterns affecting the Earth.
• Volcanic Activity or Earthquakes: Geological events that can impact the environment.
• Disease: Outbreaks that can decimate populations.

Extrinsic Factors (Extra-Terrestrial/Space)

• Comets/Meteors: Space objects that can collide with Earth.
• Exploding Star: Stellar events that could affect Earth.

Tectonic Plates

• Tectonic plates movement consists of huge, moving pieces of Earth's outer layer called the crust.
• They float on a softer layer underneath called the mantle
• Continental plates make up the land.
• Oceanic plates are situated under the oceans.
• These plates can bump into each other, slide past one another, or pull apart causing earthquakes, volcanoes, and mountains

Consequences of Tectonic Plate Shifting

• Thrusting up of mountains
• Earthquakes
• Volcanoes

Volcanoes: A Possible Cause for Cooling

• Cooling can occur due to large volumes of dust being released into the atmosphere.
• This dust can block the sun's rays, potentially leading to an Ice Age.

Continental Drift

• Continental drift causes habitat loss because species adapted to a specific climate may not survive in new conditions, leading to extinction.
• Climate changes because drifting continents affect global ocean and air currents
• Increased volcanic activity can release ash and gases into the atmosphere, blocking sunlight and cooling the Earth.
• The formation of supercontinents will result with less coastal area and more dry, inland areas on earth

Ice Age

• It represents a long-term cooling of the Earth.
• It leads to the formation of glaciers.
• Glaciers cover part of the Earth's surface for a period of time.
• Formation of glaciers will drop ocean levels, decrease in O₂ levels, increase in salt (mineral) content of oceans, and changing natural environments.

Heating of the Atmosphere

• Normally, the greenhouse effect exists, where the sun's rays enter the atmosphere, reflect off the earth, trap some in the atmosphere as longwave radiation, and help sustain life on Earth.
• The enhanced greenhouse effect where excess greenhouse gases trap more heat, resulting in rising global temperatures.

Global Heating

• Global heating is a result that may cause Disruption of habitats where species may find it hard to adapt and die.
• Changes in the timing of reproduction cycles.
• Food chain disruptions of plants and algae are temperature sensitive.
• Volcano activity can cause cooling as a result of large volumes of dust being blown into the atmosphere and blocking the sun's rays.

Disease

• Diseases can decimate populations and collapse ecosystems.
• Pathogens evolve quickly, and species do not have immunity
• Climate change can influence the presence of the pathogens to withstand climate and their effect on the survival of other organisms.

Extraterrestrial Theories

Explosion of Stars

• Can influences radiation levels on Earth

Meteor/ Asteroid Collision

• Meteor is defined a rock-like mass that falls from outer space onto Earth, larger than 1 km
• Asteroid is a larger meteor, with a diameter of more than 1km
• Comets are defined as falling stars

Meteors

• Meteors burn and glow when they enter Earth's atmosphere.
• Most disintegrate into ashes and debris.
• Some remain intact, creating craters and destroying life forms.
• They can cause dust that blocks the sun, preventing photosynthesis in plants and dropping oxygen levels.
• Tsunamis and acid rain may result
• Evidence suggests that meteors are responsible for major mass extinctions, e.g., dinosaurs at the end of the Cretaceous period ("asteroid impact theory").
• Meteors may have weakened species through global temperature changes.

Effects of a Meteorite Impact

Immediate Consequences

• Massive amounts of stone, dust, smoke, & ash are lifted into the air.
• Sunlight is blocked, preventing photosynthesis.
• Food chains collapse.

Additional Effects

• Sulfuric acid clouds form in the atmosphere.
• Sulfuric acid falls as acid rain.
• Thick clouds cool the Earth by 10–17°C.
• Clouds block sunlight.

Dinosaur Extinction

• Cooler temperatures affected dinosaurs (cold-blooded).
• Large parts of destroyed vegetation would cause fynbos biome to collapse.
• Deposits of iridium are found in rock layers from the Cretaceous period (65 mya).
• Shock quarts is glassy rock found in rocks.
• Carbon under, intense heat and pressure is found in rocks.

Evidence from Dinosaurs

• Dinosaurs died out nearly 65 million years ago
• The period of extinction is in line with evidence from fossil and geological evidence
• Chicxulub crater was found in the sea off the Yucatan Peninsula off Mexico in 1991 is the cause.
• Chicxulub crater occurred about 65 million years ago.

Meteor Impact in Gulf of Mexico

• A 200 km diameter crater in the Mexican Gulf (near Chicxulub) was caused by a meteor.
• Occurred 65 million years ago
• The impact resulted in acid rain and blocked sunlight resulting a severe temperature drop.
• Atmospheric CO2 increased and resulted in global warming.
• Final impact led to extinction for marine and land animals

Impact Details

• The asteroid travelled at 20 km per second/43,000 km per hour.
• The asteroid hit at 45-60 degree angle
• Explosions hit Earth with the force of 100,000 gigatonnes of TNT (or 10 billion Hiroshima bombs).
• It took one year for the debris to settle on the surface.

Vredefort Dome

• Vredefort Dome is located in the Free State province of South Africa.
• Crater is measured to be 10 km in diameter.
• Impact speeds occur between 10-15/sec.
• Crashed 16 km into Earth's crust
• Blasted 70km of rock as it vaporized and spread into the atmosphere
• Located 100 km from Johannesburg.
• Declared as world heritage in 2005

Cataclysmic Events Following a Collision

• Include earthquakes, giant flood waves (tsunamis), wildfires, and volcanic eruptions.

Geological Time Scale

• Paleozoic: 280-3500 mya
• Mesozoic: 135-225 mya
• Coenozoic: 0.01-65 mya

Major Extinctions:

• End of Ordovician (440 mya)
• End of Devonian (350 mya)
• End of Permian (235 mya)
• End of the Triassic (195 mya)
• End of Cretaceous (65 mya)

End of Ordovician

• This extinction occurred 440 million years ago and was the 2nd largest
• Climate Change +Ice Age+ Drop in sea level

End of Devonian

• This extinction occurred 350 mya
• Ice Age + sea level dropped

End of Permian

• This extinction occurred 235 mya
• Largest extinction with 95% of terrestrial and marine species lost
• Climate Change +Ice Age+ Sea Salinity + Volcano

End of Triassic

• This extinction occurred 195 mya
• All Amphibians extinct

End of Cretaceous

• This extiction occurred 65 mya
• Most Recent &Most Famous with 85% taxa lost
• Dinosaurs & marine ammonites extinct
• Meteorite collision + Volcano

Sixth Extinction

• This extinction has biotic causes
• The negative impact of man on earth
• 3 species/hour are lost in the current rate
• 30 000 species per year are lost in the current rate

Global Warming

• Global warming is a drastic increase that leads to Rising ocean levels, Increasing global temperatures, and Greenhouse effects
• Human influence leads to that drastic increase
• pumping greenhouse gasses into the atmosphere
• Climate change
• Pollution
• Converting of natural habitat to an argricultural area.
• Deforestation
• Introduction of alien vegetation
• Over exploitation of species
• Due to overpopulation

Extinctions/Threatened Species

Causes of extinction

• Humans disrupted the earth's carbon cycle by burning fossil fuels and releasing greenhouse gasses into the atmosphere.
• Modern climate causes uncertainty of future events
• Ex: When or if humans will disappear, a iceage may occur

Extinctions/Threatened species in SA

• Blueback
• Quagga
• Near extinction of Bontebok
• Sable Antelope
• Cycad species