Late Devonian extinction
The Late Devonian extinction was a significant global event that occurred around 375 million years ago, resulting in the extinction of approximately 70-85% of marine life. This extinction unfolded over several million years rather than in a single catastrophic event, marking it as one of the five largest extinction events in Earth's history. The Devonian Period, known as "The Age of Fish," was characterized by a vast diversity of marine species, including notable creatures like the armored fish Dunkleosteus and various trilobites.
Despite the dramatic impact on ocean life, most land animals and plants managed to survive this period. The exact causes of the Late Devonian extinction remain a matter of ongoing scientific debate, with theories suggesting factors such as drastic changes in global temperatures, excessive erosion and sedimentation, volcanic activity, or even a potential meteorite impact. A significant hypothesis points to a reduction in oxygen levels in marine environments, which would have severely affected aquatic organisms. The consequences of this extinction event were profound, leading to the loss of many coral species and a long period of diminished reef-building activity, lasting approximately 145 million years.
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Late Devonian extinction
The Late Devonian extinction was a global event that occurred approximately 375 million years ago in which about 70–85 percent of all marine life died out. Rather than occurring in a single episode, this extinction took place in several waves over the course of millions of years. The extinctions occurred during the later stages of the Devonian Period, an interval of geologic time that lasted from about 419 to 359 million years ago. Although the extinction had an indelible impact on the world and its living things, the causes remain unknown and are subject to scientific debate. The Late Devonian extinction is recognized as one of the five most destructive extinction events in Earth’s history.
Background
Life first developed on Earth more than 3.7 billion years ago. For hundreds of millions of years, life was confined to the oceans where it flourished and diversified. It later moved out onto land and continued to thrive, spreading to all parts of the planet. Modern biologists and paleontologists divide the history of Earth into categories called eons, eras, periods, and epochs. The demarcation points between some of these chronological time frames have been marked by catastrophic events in which species have suddenly disappeared, or become extinct.
At least five times throughout history, major extinction events have occurred that wiped out the majority of all living species on Earth. The causes of many of these events remain a mystery to modern science. However, they likely involved sudden climatic change and other major environmental shifts for which life was not suitably adapted.
The first major known extinction event occurred at the end of the Ordovician Period, approximately 443 million years ago. At this time, almost all life on Earth consisted of small sea creatures. Due to a catastrophic environmental change, likely involving lower temperatures and diminished sea levels, more than 85 percent of species vanished. They cease to appear in prehistoric fossils studied by modern scientists.
Despite the staggering loss of life and extreme changes to the environment, many creatures survived and adapted. Many new creatures evolved with developments that aided their survival in the prevailing circumstances. Over the course of millions of years, into the Silurian Period, the sea once again filled with life, including many varieties of creature much larger and more advanced than those of the Ordovician period.
The geological period that followed the Silurian Period is known as the Devonian Period. The Devonian Period began about 419 million years ago and was marked by an enormous variety of living things; however, it would also end in a disastrous extinction event.
Overview
The Devonian Period began during an era of flourishing life that was unprecedented at the time. The landforms of the world were situated much closer to each other than they are in modern times and were surrounded by enormous oceans. These oceans, as well as a variety of inland seas and other bodies of water, were home to a great diversity of marine creatures. Although there were some plants and animals on land, many scientists today view the Devonian Period as mainly “The Age of Fish.”
One of the most notable of these sea creatures was an enormous armored fish called Dunkleosteus, with a maximum size reaching thirty feet in length. Although these monstrous fish ruled the seas, most creatures were not as imposing. Perhaps the most distinctive Devonian sea creature was the trilobite, a small segmented arthropod with a distinctive flat exoskeleton. Other common denizens of the sea included shelled creatures such as corals, ammonites, and brachiopods.
Around 375 million years ago, near of the end of the Devonian Period, sudden changes were taking place. Over the course of several million years, great waves of extinction began impacting the planet. Most land animals and plants survived. However, the effect on sea life was calamitous. Marine life, particularly in tropical and saltwater seas, suddenly began to perish in large numbers.
Paleontologists studying the fossil record have estimated that the extinctions of the Devonian Period killed off approximately 70–85 percent of all water species that were alive at that time. That figure includes some 75 percent of all fish species, mainly the saltwater varieties. One of the most dramatic losses was that of reef-building coral and sponges, whose reefs fell into disuse for about 145 million years. Some of the other notable victims of the Devonian extinction included most groups of trilobites, including the Odontopleurid, Dalmanitid, and Phacopid families. Most brachiopods and many other kinds of shelled creatures, along with numerous species of fish and eel, mostly or entirely disappeared.
Despite the enormous effect of the Devonian extinction on the planet, its causes are poorly understood by scientists. Several factors likely occurred during the era to change the conditions of the planet and make it inhospitable, or completely uninhabitable, for the many life forms. Some of these factors may include changes in global temperature, dangerously excessive erosion and sedimentation, or volcanic eruptions. Several early theories focused on evidence that a meteorite may have struck Earth during this time, upsetting the balance of nature.
Many modern theories as to the cause of the extinction suggest that the most direct hazard to sea life was lack of oxygen. Scientists have discovered certain minerals in Devonian-age deposits that indicate a drastic reduction in oxygen in waters of that period. Without ample quantities of this gas, millions of sea creatures would have died by asphyxiation. However, the exact reason for the lack of oxygen cannot presently be determined. Scientists debate whether the cause was a sudden increase in terrestrial plants, the greenhouse effect in the atmosphere altering the climate, or some other factor not yet uncovered.
Bibliography
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