Mass Extinctions and Earth’s Ever-Changing Story

 

🌍 The Great Dying: Mass Extinctions and Earth’s Ever-Changing Story

Mass extinctions are dramatic punctuation marks in the history of life. They’ve wiped the slate clean more than once, each time setting the stage for new evolutionary chapters. This blog explores the characteristics of these extinction events and their lasting effects on Earth’s biodiversity.

📌 What Is a Mass Extinction?

A mass extinction is defined as the rapid loss of a significant percentage of biodiversity—often over 75% of species—within a short geological period (Raup & Sepkoski, 1982). These cataclysms are often global in scale and linked to large environmental disruptions, from volcanism and climate shifts to asteroid impacts.

Timeline of mass extinctions

🌀 The Big Five Extinctions

1. Ordovician–Silurian Extinction (~443 million years ago)

This event, the second-largest extinction in Earth’s history, resulted in the disappearance of about 85% of marine species. It occurred in two pulses and primarily affected marine invertebrates, including graptolites, brachiopods, and trilobites.

Causes & Characteristics:

• Triggered by a global cooling event linked to the glaciation of Gondwana.
• Rapid sea-level fall due to ice formation caused habitat loss in shallow marine environments.
• A second pulse followed a period of warming and sea-level rise, leading to ocean anoxia (Harper et al., 2014).

Reconstruction of Gondwanan glaciation

2. Late Devonian Extinction (~372–359 million years ago)

Not a single event but a prolonged crisis over ~20 million years, this extinction severely impacted reef-building organisms and jawless fishes.

Causes & Characteristics:

• Widespread anoxia in oceans due to increased nutrient runoff from terrestrial plants.
• Possibly intensified by volcanic activity and cooling episodes.
• Collapsed reef ecosystems, particularly affecting stromatoporoids and rugose corals (McGhee et al., 2013).

Devonian marine biodiversity before extinction

3. Permian–Triassic Extinction (~252 million years ago)

Nicknamed The Great Dying, this was the most devastating extinction in Earth’s history, wiping out nearly 96% of marine species and 70% of terrestrial vertebrates (Benton, 2003).

Causes & Characteristics:

• Linked to massive volcanic eruptions in the Siberian Traps.
• Resulting greenhouse gases led to extreme global warming (up to 10°C).
• Triggered acid rain, ocean acidification, and methane release from oceanic clathrates.
• Created widespread marine anoxia and terrestrial ecosystem collapse.

Eruption zone of the Siberian Traps

4. Triassic–Jurassic Extinction (~201 million years ago)

This event cleared the ecological stage for the dominance of dinosaurs. About 80% of species vanished, including many archosaur relatives.

Causes & Characteristics:

• Likely driven by volcanic outgassing from the Central Atlantic Magmatic Province (CAMP).
• Released CO₂ and sulfur aerosols, disrupting climate patterns.
• Marked by carbon isotope excursions, indicating changes in the carbon cycle (Whiteside et al., 2010).

Breakup of Pangaea and volcanic activity

5. Cretaceous–Paleogene (K–Pg) Extinction (~66 million years ago)

This is the best-known extinction, famously ending the reign of the non-avian dinosaurs. Around 75% of species were lost.

Causes & Characteristics:

• Caused by an asteroid impact at Chicxulub, Mexico.
• Created a global "impact winter" due to ejected dust blocking sunlight.
• Associated with global wildfires, tsunamis, and acid rain.
• Birds and mammals, along with many flowering plants, later diversified (Schulte et al., 2010).

Artistic depiction of asteroid impact at Chicxulub

🚨 Are We in a Sixth Mass Extinction?

Many scientists believe we are witnessing a sixth extinction driven not by natural events but by human activity. This includes:

• Habitat destruction due to deforestation and urbanization.
• Overexploitation of wildlife.
• Climate change and pollution.
• Invasive species outcompeting native organisms (Ceballos et al., 2017).

Modern extinction rates vs. background extinction rates 

🌱 Aftermath: Life Always Finds a Way

Mass extinctions are both endings and beginnings. The disappearance of dominant groups allows others to rise:

• Mammals flourished after dinosaurs vanished.
• Flowering plants expanded their range.
• New marine groups like teleost fishes diversified.

These evolutionary rebounds show the resilience of life—if given time and space.

Early mammal diversification in Paleogene

Summery in video Link

Video Link to Earth Mass Extinction Summery

📚 References

• Benton, M. J. (2003). When Life Nearly Died: The Greatest Mass Extinction of All Time. Thames & Hudson.
• Ceballos, G., Ehrlich, P. R., & Dirzo, R. (2017). Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. Proceedings of the National Academy of Sciences, 114(30), E6089–E6096.
• Harper, D. A. T., Hammarlund, E. U., & Rasmussen, C. M. Ø. (2014). End Ordovician extinctions: A coincidence of causes. Gondwana Research, 25(4), 1294–1307.
• McGhee, G. R., Clapham, M. E., Sheehan, P. M., Bottjer, D. J., & Droser, M. L. (2013). A new ecological–severity ranking of major Phanerozoic biodiversity crises. Paleogeography, Paleoclimatology, Paleoecology, 370, 260–270.
• Raup, D. M., & Sepkoski, J. J. (1982). Mass extinctions in the marine fossil record. Science, 215(4539), 1501–1503.
• Schulte, P., Alegret, L., Arenillas, I., Arz, J. A., Barton, P. J., Bown, P. R., ... & Willumsen, P. S. (2010). The Chicxulub asteroid impact and mass extinction at the Cretaceous–Paleogene boundary. Science, 327(5970), 1214–1218.
• Whiteside, J. H., Olsen, P. E., Eglinton, T., Brookfield, M. E., & Sambrotto, R. N. (2010). Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions directly linked to the end-Triassic mass extinction. Proceedings of the National Academy of Sciences, 107(15), 6721–6725.