Ordovician extinction: 480-440 million years ago
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<h1>Ordovician extinction: 480-440 million years ago</h1>
Major extinct creatures: full moon sickle, comet worm, primitive organism
The main cause of the event: gamma-ray bursts
Ordovician extinction
<h1>Gamma-ray burst hypothesis</h1>
Some scientists believe that the initial extinction may have caused gamma-ray bursts from within the supernova originating within 6,000 light-years of Earth (an arm near the Milky Way galaxy). A ten-second eruption would almost immediately deprive Earth's atmosphere of half of its ozone, exposing surface-dwelling organisms, including those responsible for planetary photosynthesis, to high levels of polar ultraviolet radiation. While this hypothesis is consistent with the pattern at the beginning of extinction, there is no clear evidence that such nearby gamma-ray bursts ever occurred.
Ordovician-Silurian extinctions, global extinctions (445200000 to 443.8 million years ago) events that occurred during the Hernand age ordovician and subsequent Rhoddanian ages (443800000 to 440.8 million years ago) of the Silurian era were the elimination of an estimated 85% of all Ordovician species. This extinction band is the second most severe, about 251 million years ago at the border between the Permian and Triassic, the percentage of affected marine households. Ordovician-Silurian extinctions were almost twice as high as they were when the K-T extinction event occurred. The Cretaceous period, about 66 million years ago, is famous for ending dinosaurs.
Brachiopods are a good demonstration of the effects of this extinction. Laurentian brachiopods have been hit hard, especially those who live in the vast shallow seas within and around the continent. Many of these brachiopods are endemic diseases of Laurentia (limited to specific areas) rather than a more international (globally distributed) form that inhabits the continental margins. After extinction, the Laurentian Ocean was refilled with brachiopod genera previously found only on other continents. Thus, the distribution of Silurian brachiopods far exceeds that of their Ordovician predecessors. Other biota — including tooth-shaped spines, acritarchs (various small micro-asbestos), bryosters, and trilobites — exhibit this regional but non-global distribution that is equally affected by this extinction event. Despite the intensity of extinction and the loss of many endemic species, The Silotian ecosystem is very similar to the Ordovician ecosystem.
In this extinction event, almost all major taxa were affected. The extinctions during this period were global, wiping out 49-60% of marine genera and nearly 85% of marine species. 、
Brachipods, bivalves, echinoderms, bryophytes and corals are particularly affected. Before the late Ordovician cooling, temperatures were relatively warm, and the suddenness of climate change and the loss of habitats caused by declining sea levels are thought to have led to extinction. Sea level drop disrupts or eliminates habitat on the continental shelf. Evidence of glaciation was found through sediments in the Sahara Desert. The combination of lower sea level and glacier-driven cooling may have been the driving factor for the Ordovician mass extinction.
Devonian extinction: 405-350 million years ago
<h1>Devonian extinction: 405-350 million years ago</h1>
Main extinct organisms: Dunn's fish, Attenborough motherfish, Titalik fish
The main cause of the event: the outbreak of the Super Mantle Pillar
Devonian extinction
In the Late Devonian, the land was colonized by plants and insects. In the ocean there are large coral reefs built by corals and stromatoporoids. Euramerica and Godwana began to integrate into Pangea. The extinction seems to have only affected marine life. Hard-hit groups include brachiopods, trilobites and reef-building organisms; The creatures that built the reef have almost completely disappeared. The cause of these extinctions is unclear. Key assumptions include sea level change and ocean hypoxia that may be triggered by global cooling or ocean volcanic activity. Others have proposed the effects of comets or other alien bodies, such as the Siljan Ring event in Sweden. Some statistical analyses suggest that the decline in diversity is caused more by a decrease in speciation than an increase in extinction. This may have been caused by the invasion of worldwide species, not by any one event. Surprisingly, the jaw vertebrates appear to be unaffected by coral reef losses or other aspects of the Kalwasser incident, while the agnathans had declined long before the end of Flasnian.
<h1>Duration and duration of the extinction event</h1>
The extinction rate appears to be higher than the background rate, extending the interval between the last 20-25 million years of the Devonian Period. During this time, about eight to ten different events can be seen, two of which are particularly severe. [15] Biodiversity was lost for longer periods of time before the Kalwasser incident. The fossil record for the first 15 million years of the Carboniferous period is largely devoid of fossil land animals, possibly related to the losses in the final Devonian Hangenberg event. This period is known as Romer's Gap.
<h1>The impact of the event</h1>
Extinction events are accompanied by widespread ocean hypoxia ; That is, hypoxia, decay is prohibited and the preservation of organic matter is allowed. This, combined with the ability of porous reef rocks to retain oil, led to Devonian rocks becoming an important source of oil, especially in the United States.
<h1>Causes of extinction</h1>
Since the Killwasser-related extinctions occurred over such a long period of time, it is difficult to assign a cause, in effect separating the cause from the effect. Sedimentary records show that the Late Devonian was a period of environmental change that directly affected organisms and led to extinction. The reasons for these changes are more controversial.
From the end of the Middle Devonian to the Late Devonian, several environmental changes can be found in sedimentary records. Evidence of widespread hypoxia in seafloor waters; Carbon burial rates are rising and benthic organisms are being destroyed, particularly in the tropics, especially coral reef communities. Sufficient evidence of high-frequency sea level changes around the Frasnian-Famennian Kellwasser event, one of which was associated with the occurrence of hypoxic sediments, has been found. The Hangenberg event was associated with sea level rise, followed by glacier-related sea level decline
Permian mass extinction: 299-250 million years ago
<h1>Permian mass extinction: 299-250 million years ago</h1>
Main extinct organisms: trilobites, sea crabs and important coral taxa
The main cause of the incident: air and seawater pollution in Siberian volcanoes
There is evidence that there are one to three distinct extinction pulses or stages. The latter's proposed mechanisms include one or more large meteor impact events, such as massive volcanic activity in the Siberian Trap, and consequent coal or gas fires and explosions, and methane-producing microorganisms, known as methanogenic bacteria, according to the clathrate gun hypothesis, and the runaway greenhouse effect triggered by the sudden release of methane from the seafloor due to the dissociation of methane clathrates. Possible gradual changes include changes in sea level, increased hypoxia, increased droughts, and changes in ocean circulation caused by climate change.
Determining the exact cause of the Permian-Triassic extinction event is difficult, mainly because the disaster occurred 250 million years ago, and since then, many of the evidence pointing to this cause has been destroyed or hidden in the depths. The Earth is under many layers of rock. The seafloor is also completely every 200 million years through the ongoing process of recovering plate tectonics and seafloor expansion, leaving no useful indication under the ocean.
Scientists have accumulated quite a bit of evidence of the cause, and several mechanisms for extinction events have been proposed. These proposals include catastrophic and progressive processes (similar to the theory of Cretaceous-Paleogene extinction events).
The catastrophic group consists of one or more large fireballs impact events, increased volcanoes, and the sudden release of methane from the seafloor, either due to the dissociation of methane hydrate deposits or the metabolism of organic carbon deposits by methane microorganisms.
This gradual group includes sea level changes, increased hypoxia, and increased drought.
Any hypothesis about the cause must explain the selectivity of the event, which has the most severe effect on calcium carbonate bone organisms; Long-term (4 to 6 million years) before recovery begins, once recovery begins, the minimum degree of biomineralization (despite inorganic carbonate deposition).
Triassic extinction: 250-203 million years ago
<h1>Triassic extinction: 250-203 million years ago</h1>
Main extinct creatures: Horned crocodile, Post crocodile, spirit crocodile, wild tooth crocodile
The main causes of the event: steam, magma, toxic gases
The Triassic-Jurassic extinction event marked the boundary between the Triassic and Jurassic periods, 201.3 million years ago, and was the primary extinction event in the Ezoospanic, profoundly influencing land and sea life. In the ocean, the entire class (tooth-shaped spines) and 23-34% of the marine genus disappeared. On land, all dragons and Avemetatarsalia (pterosaurs and dinosaurs) except crocodiles (Sphenosuchia and Crocodyliformes), some of the remaining thethersids and many large amphibians went extinct.
<h1>Several explanations for this incident have been proposed, but all have unresolved questions:</h1>
In the late Triassic period, gradual climate change, sea level fluctuations or ocean acidification pulses [9] reached a tipping point. However, this does not explain the suddenness of extinctions in the marine field.
Asteroid impacts, but to date no craters of sufficient size coincide with the Triassic-Jurassic boundary.
Large-scale volcanic eruptions, particularly flooded basalts in the Mid-Atlantic Magma Province (CAMP), will release carbon dioxide or sulfur dioxide and aerosols, which will lead to intense global warming (from the former) or cooling (from the latter). CAMP degassing records show that after each major magmatic action pulse, there are several different carbon dioxide pulses, at least two of which are equivalent to doubling the atmospheric CO2.
The isotopic composition of Triassic and Early Jurassic fossil soils is associated with large negative carbon isotope shifts (Whiteside et al., 2010). Carbon isotopes of lipids (n-alkanes) derived from yelsin and lignin, as well as total organic carbon from two parts of lake sediments interlayed with CAMP in eastern North America, have shown carbon isotope shifts similar to those of most marine Saint-Audrey. Bay Section, Somerset, England; Correlation suggests that the end-Triassic extinction event occurred in both marine and terrestrial environments, slightly higher than the oldest basalt in eastern North America, but at the same time as the oldest turbulence in Morocco (also proposed by Deenen et al., 2010), with both a critical CO2 greenhouse and a marine biocalcification crisis.
Simultaneous CAMP eruptions, mass extinctions, and carbon isotope drift all show up in the same place, making them volcanic causes of mass extinction. The catastrophic dissociation of natural gas hydrates (suggested as one possible cause of the largest species extinction ever recorded, the so-called "Great Near Death" at the end of the Permian) may have exacerbated greenhouse conditions.
Cretaceous extinction: 137 million to 65 million years ago
<h1>Cretaceous extinction: 137 million to 65 million years ago</h1>
The main extinct creature: dinosaurs
The main cause of the event: meteorite impacts caused the collapse of global ecosystems
Many species died during the Cretaceous Tertiary (K-PG) extinction event, most notably non-avian dinosaurs. It also destroys too many other terrestrial creatures, including certain mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K-Pg extinction killed plesiosaurs and giant marine lizards (Mosasauridae) and destroyed fish, sharks, mollusks (especially ammonites), which are extinct), as well as many species of plankton. It is estimated that 75% or more of all species on Earth have disappeared. However, extinction also offered evolutionary opportunities: with it, many groups experienced significant adaptive radiation – the emergence of new forms and species in fragmented and empty ecosystems. Mammals, in particular, diversified in the Paleogene, evolving into new forms such as horses, whales, bats, and primates. Birds, fish, and lizards also radiate.
Extinction events are severe, global, rapid and selective, wiping out a large number of species. According to marine fossils, it is estimated that 75% or more of all species are extinct.
The event appears to have affected all continents at the same time. For example, non-avian dinosaurs came from Maastrichtian in North America, Europe, Asia, Africa, South America, and Antarctica, but the Cenozoic nowhere in the world is aware of it. Similarly, fossil pollen shows the destruction of plant communities in regions such as New Mexico, Alaska, China, and New Zealand.
Despite the severity of the event, there are significant differences in the rate of extinction between and within different evolutionary branches. As atmospheric particles block sunlight and reduce solar energy reaching the ground, species that rely on photosynthesis decrease or become extinct. This plant extinction led to a major restructuring of the main flora. Omnivores, carnivores, and carrion foods survived extinction events, possibly because of an increase in food sources. It seems that no purely herbivorous or carnivorous mammals have survived. Instead, surviving mammals and birds feed on insects, worms and snails, and in turn feed on detritus (dead plant and animal matter).
<h1>duration</h1>
The rate of extinction is a controversial issue, as some theories about the causes of extinction mean rapid extinction in a relatively short period of time (from years to thousands of years), while others mean longer periods. Due to the influence of Signal-Lipps, this problem is difficult to solve; That said, the fossil record is so incomplete that most extinct species may have disappeared long after the recently discovered fossils. Scientists also found few consecutive fossil-bearing rock beds that covered millions of years before K-Pg's extinction to millions of years after. [28] The rate and thickness of settlement of K-Pg clay from three sites indicate rapid extinction, possibly less than 10,000 years. In one place in the Denver Basin of Colorado, the "fern spike" lasted about a thousand years (no more than seventeen thousand years); After the deposition of the K-Pg boundary layer, the earliest Cenozoic mammals appeared for about 185,000 years (no more than 570,000 years).