Mass extinction

Also called: Big Five extinctions · Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Beyond NCERT

Meaning

A mass extinction is an event in which a large share of the world's species die out in a short geological time, often within a few thousand to a few hundred thousand years. Five such events, the "Big Five", stand out in the fossil record: the end-Ordovician, Late Devonian, end-Permian, end-Triassic and end-Cretaceous. They matter because they mark the main breaks in the history of life, and two of them close whole eras on the geological time scale.

Explanation

How a mass extinction happens (cause → process → result)

• Cause: a sudden shock to the whole planet. The main triggers in the Big Five were:
• flood basalt volcanism: lava pours out of long cracks in the ground, layer after layer, over huge areas
• an asteroid impact

• an ice age with a fall in sea level

• Process: the climate changes faster than life can adapt.

• Volcanoes release carbon dioxide and sulphur gases.
• Dust and gases block sunlight, or the extra gases warm the world.

• The oceans turn acidic and lose oxygen.

• Result: food chains break.

• Photosynthesis (plants using sunlight to make food) slows down or collapses.
• Many groups of plants and animals die out together, all over the world.
• The survivors spread out and fill the empty places. This is why each extinction starts a new chapter of life.

The Big Five, oldest to youngest

#	Event	Approximate time	Likely cause
1	End-Ordovician	about 445 million years ago	Ice age and a fall in sea level
2	Late Devonian	about 372 million years ago	Ocean oxygen loss; a series of crises
3	End-Permian ("Great Dying")	about 252 million years ago	Siberian Traps volcanism
4	End-Triassic	about 201 million years ago	Volcanism as Pangaea split
5	End-Cretaceous (K–Pg)	66 million years ago	Chicxulub impact plus Deccan Traps

• Link to the time scale:
• The end-Ordovician and Late Devonian events fall inside the Palaeozoic era ("old life").
• The end-Permian event closes the Palaeozoic (539–252 million years ago).
• The end-Triassic event falls inside the Mesozoic era ("middle life").
• The end-Cretaceous event closes the Mesozoic (252–66 million years ago) and opens the Cenozoic era ("new life").

End-Permian: the worst of all

• Siberian Traps: a huge area of flood basalt in Russia.
• The chain of events:
• Huge eruptions released carbon dioxide and sulphur gases.
• The world warmed, and the oceans turned acidic and lost oxygen.

• About 90% of sea species died out.

• This is why it is called the "Great Dying".

End-Cretaceous: the end of the dinosaurs

• Chicxulub impact: an asteroid strike 66 million years ago at the north-western tip of Mexico's Yucatan Peninsula. The crater faces the Gulf of Mexico [1].
• Size: the crater is about 180 km wide and about 900 m deep. It lies under about 1 km of younger rocks and sediments, so it went undetected for decades [2].
• Cause → process → result:
• Cause: an asteroid hits the Earth at very high speed.
• Process: a global cloud of dust and sulphur gases blocks sunlight, and the Earth goes through about a decade of near-freezing temperatures [2].

• Result: photosynthesis collapses and food chains break. The non-bird dinosaurs die out, along with about 75% of all other species [2].

• Deccan Traps as an added stress:

• The Deccan Traps erupted around the same time, and their gases added climate stress.

• Scientists still see the impact as the main cause.

• Birds are the dinosaur line that survived.

Where it occurs

• Siberian Traps, Russia: the flood basalts behind the end-Permian "Great Dying", about 252 million years ago.
• Chicxulub crater, Yucatan Peninsula, Mexico: at the north-western tip of the peninsula, facing the Gulf of Mexico [1]. It marks the end-Cretaceous impact 66 million years ago.
• Deccan Traps, India: flood basalts in western and central India, mostly in Maharashtra. They were an added stress during the end-Cretaceous extinction. In India's rock systems they belong to the Aryan group, along with the Gondwana and Tertiary rocks.
• Pangaea: the single supercontinent. Volcanism as it began to split (about 200 million years ago) is linked to the end-Triassic extinction. It split into Laurasia (north) and Gondwanaland (south).
• The world today: many scientists call the current fast, human-driven loss of species a possible sixth mass extinction.

Don't confuse with

• End-Permian vs End-Cretaceous: the end-Permian (about 252 million years ago, Siberian Traps) was the worst mass extinction. The end-Cretaceous (66 million years ago, Chicxulub) is the most famous because it killed the dinosaurs, but it was not the biggest.
• Siberian Traps vs Deccan Traps: the Siberian Traps (Russia) were the main cause of the end-Permian event. The Deccan Traps (India) were only an added stress at the end-Cretaceous. The Chicxulub impact was the main cause there.
• Cambrian explosion: the opposite kind of event. Around 539 million years ago, animals with hard parts spread fast. It marks the start of the Phanerozoic eon and the Palaeozoic era. It is not a die-off.
• Sixth mass extinction vs Anthropocene: the "sixth mass extinction" is a scientific view about today's loss of species. The Anthropocene was a proposed epoch that the SQS rejected on 5 March 2024 [1]. We still officially live in the Holocene epoch, Meghalayan age.

Prelims Hooks

• Order of the Big Five (oldest → youngest): End-Ordovician → Late Devonian → End-Permian → End-Triassic → End-Cretaceous.
• Worst mass extinction: end-Permian, the "Great Dying" (about 252 million years ago). It wiped out about 90% of sea species, was linked to the Siberian Traps, and closed the Palaeozoic era.
• Event → cause match: End-Ordovician → ice age and sea-level fall. Late Devonian → ocean oxygen loss. End-Permian → Siberian Traps. End-Triassic → volcanism as Pangaea split. End-Cretaceous → Chicxulub impact plus Deccan Traps.
• Chicxulub crater: Yucatan Peninsula, Mexico, about 180 km wide, 66 million years ago [2]. Non-bird dinosaurs and about 75% of other species died out [2].
• Trap: "The Deccan Traps alone caused the extinction of the dinosaurs." This is wrong. The Chicxulub impact was the main cause, and the Deccan Traps added stress.
• Era boundaries: the end-Permian extinction marks the Palaeozoic–Mesozoic boundary (252 million years ago). The end-Cretaceous (K–Pg) extinction marks the Mesozoic–Cenozoic boundary (66 million years ago).

Mains Points

• The Earth's interior and outside events as drivers of extinction (GS-I):
• Flood basalts (Siberian Traps, Deccan Traps) and asteroid strikes (Chicxulub) changed the climate quickly.
• They worked through gases, darkness, acid oceans and oxygen loss.

• This shows that volcanic activity and outside events have shaped the history of life on Earth.

• Lessons from the past for today's climate change (GS-III):

• The end-Permian chain (more carbon dioxide → warming → acid oceans → oxygen loss) looks like today's human-caused stresses.
• This supports the view that the world may be in a sixth mass extinction.

• It strengthens the case for global action under the CBD and UNFCCC.

• Geo-heritage value of India's rock record (GS-I/GS-III):

• The Deccan Traps of Maharashtra hold a record of the end-Cretaceous crisis.
• Protecting such rock and fossil sites helps scientists study past extinctions.

Related concepts

• Chicxulub impact
• Lonar crater
• Meghalayan age
• Anthropocene

Read more

• The geological time scale, impacts, extinctions and the Anthropocene