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Late Devonian Extinction

The Late Devonian Extinction, occurring around 359 million years ago, is one of the major mass extinction events in Earth’s history. This event marked the end of the Devonian Period and had a significant impact on marine and terrestrial life.

Timing and Duration

The Late Devonian Extinction took place over a relatively extended period, spanning from the Late Frasnian to the Early Famennian stages of the Late Devonian. This event occurred around 359 million years ago.

Two-Pulse Extinction

The Late Devonian Extinction is often divided into two distinct extinction pulses, each affecting different groups of organisms. The first pulse, known as the “Kellwasser Event,” primarily impacted marine life, including coral reefs, ammonites, and brachiopods. The second pulse affected a broader range of marine and terrestrial organisms, with a focus on marine species such as trilobites and jawless fish.

Causes and Triggers

Several factors are believed to have contributed to the Late Devonian Extinction, though the exact causes remain subject to ongoing research and debate. Some of the proposed triggers include:

  1. Climate Change: During the Late Devonian, the climate experienced fluctuations, including periods of warming and cooling. Changes in sea levels and ocean circulation patterns could have disrupted ecosystems and habitats.
  2. Anoxic Events: Anoxic (low oxygen) conditions in marine environments may have been exacerbated by increased nutrient runoff from land, leading to the expansion of anoxic zones. These conditions could have stressed marine organisms and contributed to extinctions.
  3. Global Cooling: The Late Devonian was marked by a cooling trend, which may have impacted species adapted to warmer conditions. Glacial events and associated sea-level changes could have disrupted ecosystems and reduced available habitats.
  4. Impact Events: Although not as prominent as in other mass extinctions, impact events (such as asteroid or comet impacts) have been proposed as potential triggers. However, direct evidence for impact events during this period is limited.

Impact on Life

The Late Devonian Extinction had varying impacts on different groups of organisms. Marine life, particularly coral reefs, brachiopods, ammonites, and some fish, experienced significant declines in diversity. Terrestrial ecosystems were also affected, with some amphibian groups facing declines.

Survivors and Recovery

Despite the significant loss of biodiversity, many groups of organisms managed to survive the Late Devonian Extinction. During the subsequent Carboniferous Period, life rebounded and underwent diversification, with new species emerging to fill the ecological niches left vacant by the extinctions.

Geological Record

The evidence of the Late Devonian Extinction is preserved in the geological record as changes in fossil assemblages, sedimentary facies, and isotopic signatures. The two extinction pulses are marked by distinct layers of sedimentary rock that contain fewer or different types of fossils compared to surrounding layers.