Oceanic Anoxic Event 1a and MASS EXTINCTION

Oceanic Anoxic Event 1a from the Paris Basin (Environment) Paper-3 PMP

OAE 1a refers to a period during the Cretaceous Period (145 million years ago and ended 66 million years ago) when Earth's oceans became depleted of oxygen, causing a significant disruption in marine life.

Cause: The event is believed to have been triggered by massive volcanic eruptions that released significant amounts of carbon dioxide (CO?), leading to global warming and oxygen depletion in the oceans, which subsequently resulted in the formation of anoxic marine basins.

Impact: CO2 in seawater forms carbonic acid, dissolving sea creatures' shells and lowering oxygen levels. This oxygen depletion led to the extinction of marine species, particularly plankton, and caused the formation of organic carbon-rich layers known as black shales.

A recent study published in Science Advances has refined the timing and duration of Ocean Anoxic Event 1a (OAE 1a) by analyzing prehistoric rocks and fossils from Mount Ashibetsu, Japan.

Anoxic marine basins: Bodies of water, often in deep ocean regions, where oxygen levels are extremely low or absent.
- Characteristics: Favor the survival of specialized microbes and fungi while inhibiting most aerobic life forms.
- Carbon Sequestration: Low oxygen levels slow the decomposition of organic matter, aiding in long-term carbon sequestration, which helps reduce atmospheric CO? levels.
- Examples: Black Sea, Cariaco Basin (Caribbean Sea), and Orca Basin (Gulf of Mexico).

Key Highlights of the Recent Study

Timing: The event began 119.5 million years ago, confirmed through isotopic analysis of volcanic tuffs from Japan’s Hokkaido Island.
- OAE 1a lasted approximately 1.1 million years, indicating the extended recovery period for oceans after CO?-driven warming and anoxia.
Volcanic activity: Linked to massive volcanic eruptions, such as the Ontong Java Nui complex, which released significant CO? into the atmosphere and oceans.
Modern relevance: Highlights parallels between ancient volcanic CO? emissions and current human-induced warming.

Warns that rapid modern warming could trigger similar disruptions in marine ecosystems and potentially lead to a Holocene extinction event.

Major Mass Extinction Events on Earth?

Ordovician-Silurian Mass Extinction (443 million years ago):
- Impact: Wiped out approximately 85% of all species.
- Cause: Dramatic temperature drop and glaciation, leading to sea level fall, followed by rapid warming.
Devonian Mass Extinction: Occurred 374 million years ago:
- Impact: Killed about three-quarters of Earth's species, mostly marine invertebrates.
- Cause: Environmental changes such as global warming, and cooling, fluctuating sea levels, and reduced atmospheric oxygen and carbon dioxide. Exact triggers of the extinction remain unclear.
Permian Mass Extinction (250 million years ago):
- Impact: Known as "The Great Dying," it eradicated over 95% of species, including most vertebrates.
- Cause: It is linked to massive volcanic eruptions in the Siberian Traps, Russia, causing global warming and ocean anoxia. Volcanism, climate shifts, and a potential asteroid impact likely exacerbated the catastrophe.
Triassic Mass Extinction (200 million years ago):
- Impact: Eliminated about 80% of species, including many dinosaurs.
- Cause: Extensive geological activity that raised carbon dioxide levels, global temperatures, and caused ocean acidification.
Cretaceous Mass Extinction (66 million years ago):
- Impact: Killed 78% of species, including non-avian dinosaurs.
- Cause: Likely caused by an asteroid impact in Mexico, creating a massive crater, global cooling, and ecosystem collapse. Additionally, volcanic eruptions in India's Deccan Plateau may have worsened the event by contributing to global warming.

Holocene Extinction?

About: The Holocene Extinction, also known as the Sixth Mass Extinction, refers to the ongoing extinction event that began around 12,000 years ago and is largely attributed to human activities, unlike previous mass extinctions, which were caused by natural phenomena.

Holocene Extinction Events:

- The Megafauna Extinction (12,000 years ago) wiped out large mammals like mammoths and saber-toothed cats, likely due to human hunting and climate change.
- Coral Reef Bleaching is driven by rising sea temperatures and ocean acidification, endangering reef biodiversity.
- Amphibian Declines, especially frogs, are caused by habitat loss, pollution, and diseases like chytridiomycosis.
Impact: The current extinction rate is 1,000-10,000 times higher than natural rates.
- Ecosystem services, such as food production, clean water, and air, are at risk, threatening both biodiversity and human life.
Efforts to Mitigate the Holocene Extinction: Strengthen commitments to cut carbon emissions and limit global warming to 1.5°C, as outlined in the Paris Agreement.
- Collaborate globally to conserve at least 30% of lands, inland waters, and oceans, as under the 30X30 Initiative.
- Encourage individuals, businesses, and communities to adopt sustainable practices and demand accountability from governments and corporations.

Source: Science direct

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