MASS EXTINCTIONS AND THEIR CAUSES

Mass extinctions and their causes

• Mass extinctions are important occurrences in Earth's history that cause a great number of species to perish in a short period of time.
• Understanding these occurrences is critical to comprehending the processes of biodiversity, evolution, and ecological equilibrium.

1. Mass extinctions

• A mass extinction is when at least 75% of a species on Earth becomes extinct.
• Historical context: Earth's five great mass extinctions shaped life's development.

2. The Big Five Mass Extinctions

1. The Ordovician-Silurian Extinction occurred around 443 million years ago

• Caused by climate change and declining sea levels.
• Approximately 85% of species, including marine species, were gone.

2. Late Devonian Extinction (about 375 million years ago)

• Possible causes include climate change, low oxygen levels, and asteroid impacts.
• The extinction of about 75% of species had a profound impact on marine life.

3. The Permian-Triassic Extinction occurred around 252 million years ago

• Causes include volcanic eruptions, climatic change, and ocean anoxia.
• The most devastating extinction, with approximately 96% of all species being extinct.

4. Triassic-Jurassic Extinction (about 201 million years ago)

• Causes include volcanic activity and climate change.
• Dinosaurs arose as a result of the extinction of around 80% of species.

5. The Cretaceous-Paleogene Extinction occurred around 66 million years ago

• Cause: meteor impact and volcanic activity.
• Impact: Approximately 75% of species, including dinosaurs, were eradicated.

3. The causes of mass extinctions.

• Mass extinctions are caused by a multitude of factors, many of which are connected.

The key factors are:

a. Environmental changes

• Climate Change: Temperature fluctuations can affect ecosystems and food supplies.
• Sea level fluctuations can harm coastal and marine habitats.
• Increased CO2 levels cause ocean acidification, hurting marine life.

b. Asteroid impacts

• Impact craters indicate that asteroid or comet encounters can cause catastrophic extinctions.
• The Chicxulub impact played a crucial role in the demise of dinosaurs.

c. Volcanic Activity

• Large eruptions can emit gases that disrupt climatic patterns, causing habitat loss.
• The Siberian Traps eruption corresponds to the Permian-Triassic extinction.

d. Biological factors

• Invasive species can compete with native species in new areas.
• Disease outbreaks may destroy populations, especially if species lack resistance.

4. Implications for Biodiversity

• Loss of biodiversity can render ecosystems vulnerable and less responsive to change.
• The extinction of one species can set off a chain reaction that affects several others.

IMAGE SOURCE (THUMBNAIL)