Understanding Extinction and Earth's Structure

Glossary of Extinction

• Extinction occurs when all living individuals of a particular type die out and no longer exist on earth.
• Background extinctions represent the natural, continuous rate at which species disappear.
• Mass extinctions are periods where most of Earth's life forms die out, leading to a crash in biodiversity.
• Extinctions can be caused by environmental disasters such as meteor impacts, or the failure of species to adapt to sudden environmental changes, such as ice ages where ectotherms struggle with declining temperatures.

Mass Extinction Impact

• During a mass extinction event, 70% to 90% of all life on Earth is eliminated.

Earth's Structure

• The crust is the outermost layer of the Earth, made of solid rock and minerals, partially covered by water, and broken into shifting tectonic plates.
• The mantle is a very hot layer of semi-solid rock that moves slowly, influencing the movement of tectonic plates above it.
• The core consists of a melted metal outer core and a solid inner core made of iron and nickel.
• Intrinsic factors are terrestrial or earthly causes, while extrinsic ones are extraterrestrial or space-related.

Intrinsic Factors of Mass Extinction

• Plate tectonics involve the movement of Earth's crust.
• Continental drift is the gradual shifting of continents.
• Climate changes include the heating and cooling of the Earth.
• Volcanic activity and earthquakes are geological events.
• Diseases can also contribute to extinctions.

Extrinsic Factors of Mass Extinction

• Comets and meteors striking Earth.
• Exploding stars impacting Earth.

Tectonic Plate Movement

• Tectonic plates, large moving pieces of Earth's outer layer (crust), float on the softer mantle layer below.
• Continental plates make up the land, while oceanic plates lie under the oceans.
• Plate movements can cause earthquakes, volcanoes, and mountain formation.
• Plate shifting can cause the thrusting up of mountains, as well as earthquakes and volcanoes.

Volcanoes

• Volcanoes can cause cooling of the earth.
• Volcanoes release large volumes of dust into the atmosphere, in turn blocking the sun's rays.
• Blocking the sun's rays leads to a potential ice age.

Continental Drift Effects

• Continental drift is the movement of separate parts of Earth's crust over time.
• Habitat loss occurs as species adapted to a specific climate may not survive new conditions.
• Climate changes arise as drifting continents alter global ocean and air currents, changing climate patterns.
• Increased volcanic activity happens, releasing ash and gases, blocking sunlight, cooling the Earth, and disrupting food chains.
• Supercontinents form when continents merge, reducing coastal area and increasing dry, inland regions.

Climate Change

• The heating and cooling of the atmosphere occur in repeating cycles.
• Glaciers are large ice accumulations mixed with snow, rock, sediment, and liquid water.
• Glaciers form on land and move downslope due to weight and gravity, covering parts of Earth's surface.

Ice Age Consequences

• Ice age causes dropping ocean levels
• Ice age causes a decrease in oxygen levels
• Ice age causes an increase in salt content in oceans
• Natural environments change during ice ages

The Greenhouse Effect

• Solar rays enter the atmosphere and reflect off the earth.
• Some are trapped by greenhouse gases.
• It is a natural process that warms the atmosphere to sustain life.
• More heat is trapped with more greenhouse gases, causing global temperatures to rise.

Global Warming

• Warmer climates change food chains.
• Habitats of some organisms are disrupted or disappear entirely in turn making it difficult for species to adapt and survive
• There are changes in timing of reproduction of species.
• The food chain is disrupted as plants and algae are temperature sensitive.
• Volcanoes can be a possible cause for cooling the earth by releasing volumes of dust, which blocks the sun’s rays.

Disease and Ecosystems

• Diseases can lead to the collapse of ecosystems by decimating populations.
• Pathogens can evolve in turn exploiting species with little immunity.
• A change in climate influences the presence of pathogens in environment, affecting their survival and impact on other organisms.

Extraterrestrial Theories

• Extraterrestrial theories include explosions of stars, which influence radiation levels on Earth, and meteor/asteroid collisions.
• A meteor is a rock-like mass from outer space that falls onto Earth, larger than 1 km.
• An asteroid is a larger meteor (more than 1 km in diameter).
• Comets can also be a factor, as their falling stars can influence the radiation levels on Earth.

Meteors

• Meteors burn and glow upon entering Earth's atmosphere.
• Most of them disintegrate into ashes and debris.
• Some remain intact, thus creating craters.
• Meteors may destroy life forms.
• They cause dust, thereby, blocking sunlight.
• No photosynthesis occurs in plants when sunlight is blocked.
• They can cause a drop in oxygen levels as well as tsunamis & acid rain.

Meteorite Theory

• Meteorite theory states that deposits of iridium in rock layers (65 mya), shock quarts in rocks, and carbon formed under intense heat provides evidence for meteorite theory.
• Growing evidence indicates meteors caused some major mass extinctions, such as the extinction of dinosaurs.
• Asteroid hitting the earth caused many of the major mass extinctions.

Chicxulub Crater

• Dinosaurs became extinct about 65 million years ago
• This date is confirmed by fossil and geological evidence
• The Chicxulub crater was discovered off the Yucatan Peninsula in Mexico in 1991 and is about 65 million years old
• It is a 200 km diameter crater in the Mexican Gulf
• The crater was caused by a 10-18km diameter meteor impact of 65 million years ago
• The impact caused acid rain and ash, blocking sunlight and causing global cooling (nuclear winter)
• There was an increase in atmospheric carbon dioxide, resulting in global warming, which delivered the final impact on dinosaurs

Asteroid Impact Details

• The asteroid was travelling at 20 kilometers per second (43000 kilometers per hour) at an angel of 45-60 degrees causing the earth with a force of 100,000 gigatonnes of TNT.
• Earth’s debris would settle in approximately 1 year.
• Meteor impact lead to catastrophic loss of life of multiple species.

Vredefort Dome

• Vredefort Dome is a crater, 10 km in diameter, formed with impact speed of 10-15 km per second, 16 km into earth’s crust.
• The blast of impact caused 70km³ of rock to vaporise and to spread into the atmosphere.
• Vredefort Dome is located 100 km South of Johannesburg and was declared a World Heritage Site in 2005.

Cataclysms resulting from Meteor collision

• Meteor collisions can also lead to earthquakes, giant flood waves, wildfires, and volcanic eruptions.
• One mass extinction theory links meteor collisions with volcanic eruptions.

Timeline of Mass Extinctions

• The timeline of the Paleozoic Era is between 280-3500 mya
• The timeline of the Mesozoic Era is between 135–225 mya
• The timeline of the Coenozoic Era : is between 0,01–65 mya
• All the causes were caused by PHYSICAL causes.

Five Major Extinctions

• The end of Ordovician period occurred 440 mya with climate change, ice age, & drop in sea level.
• The end of Devonian occurred 350 mya with ice age & drop in sea level.
• The end of Permian occurred 235 mya. The largest extinction occurred when there was 95% species loss, with climate change, ice age, & drop in sea level.
• The end of Triassic occurred 195 mya and all amphibians became extinct with ice age & volcano
• The end of Cretaceous occurred 65 mya. It was the most recent & most famous when 85% species, dinosaurs & marine ammonites became extinct through meteorite collision and volcanoes.

The Sixth Extinction

• The negative impact of human activities on Earth.
• Sixth extinction is only caused by biotic factors.
• The current rate of extinction is three species per hour or 30 000 per year

Global Warming Impact

• Global warming is an increase in ocean levels and global tempuratures through greenhouse gases.
• There is a dramatic increase and influence from humans in extinction of species.
• Industrial activities and pumping greenhouse gases into the atmosphere causes changes in climate and pollution
• Natural environments and habitats are also being changed.

Human Influence on Extinction

• Humans have influenced the drastic increase in extinction of species through natural environments and habitats being changed into food-producing agricultural areas.
• Deforestation is also a factor, so is the introduction of alien vegetation.
• Over-exploitation of species and overpopulation contribute to the extinction of species as well.

Extinctions in South Africa

• Extinctions/threatened species in South Africa include the Bluebuck, Quagga, many frog species, with the near extinction of Bontebok and Sable Antelope.
• Many Cycad species, and/or some Proteas and bulbs are threatened as well.

Extinctions Today

• The uncertainty of the modern climate reflects the uncertainty of future climate.
• If humans disappeared, the climate may cool off into an ice age, as thought in the past.
• Burning fossil fuels releases gases in the atmosphere, thereby disrupting earth’s carbon cycle, which is also caused by burning fossil fuels.