Mass Extinction in the Devonian: Unraveling the Mysteries
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Chapter 1: Understanding the Devonian Period
The Devonian Period was a time of remarkable diversification for both plant and animal life, featuring extensive adaptive radiation in marine and terrestrial ecosystems. However, this success ultimately led to a catastrophic decline.
This section will delve into the slow decline of life during the Late Devonian, emphasizing that the extinction event was not a sudden catastrophe but a gradual deterioration.
Section 1.1: The Extinction Event
Between 383 and 359 million years ago, a staggering 70 to 80 percent of Earth's species vanished. Yet, the precise reasons behind this mass extinction remain elusive. Some suggest that life was thriving to such an extent that it created conditions detrimental to survival, drawing parallels to the Anthropocene extinction caused by human activities.
Subsection 1.1.1: The Timeline of Extinction
The Late Devonian is categorized into two main stages: the Frasnian and the Famennian, covering a span of 24 million years. Paleontologists have identified three key moments within this period where significant fossil record changes occurred, marked by substantial species loss.
Section 1.2: The Gradual Nature of Extinction
The decline of species during the Late Devonian resembled a series of gradual setbacks rather than a singular catastrophic event. Unlike the dramatic asteroid impact that led to the Cretaceous extinction, evidence from various impact craters suggests that they were not the main cause of this earlier mass extinction.
Chapter 2: Environmental Conditions of the Devonian
The first video titled "Mass Extinction Events from the Devonian to Jurassic that Nobody Talks about!" provides an insightful overview of the lesser-known extinction events during this critical period.
The environmental conditions of the Late Devonian were characterized by significant chemical and ecological imbalances. This culminated in habitats becoming increasingly inhospitable to life.
The second video, "Late Devonian Mass Extinction Event ~360 Million Years Ago | GEO GIRL," explores the details surrounding the Devonian extinction and its implications on marine life.
Organic Shales and Anoxia
Shales are fine-grained sedimentary rocks formed from sediments accumulated over millennia. A particular type, known as black shale, is prized by the oil industry due to its high organic content. When buried and subjected to heat, these shales can generate oil, serving as a crucial indicator of ancient environmental conditions.
The presence of black shales suggests that during the Late Devonian, conditions were often anoxic, meaning most marine life could not survive due to a lack of free oxygen. The widespread occurrence of these deposits across the eastern United States points to severe ecological stress in the oceans.
Late Devonian Anoxia: Causes and Effects
Various factors can lead to ocean anoxia, and understanding these is essential. For example, modern cases like the Black Sea demonstrate how stratification can prevent oxygen from reaching deeper waters.
However, anoxic conditions can also arise in unstratified bodies of water. In nutrient-rich environments, algal blooms can occur, leading to oxygen depletion as bacteria break down the excessive organic matter.
During the Devonian, the rapid evolution of terrestrial plants, which helped create soil and transport organic material to the oceans, played a significant role in these dynamics. As forests flourished, the runoff into the oceans increased, contributing to the conditions ripe for mass extinction.
(Next — Was there more bad news in the Late Devonian?)
Sources: - The Devonian extinction saw the oceans choke to death (By Chris Baraniuk, BBC) - Oxic, Suboxic and Anoxic Conditions in the Black Sea (by James W. Murray et al.)