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An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.
The Holocene extinction, or Anthropocene extinction, is the ongoing extinction event caused by humans during the Holocene epoch. These extinctions span numerous families of plants and animals, including mammals, birds, reptiles, amphibians, fish, and invertebrates, and affecting not just terrestrial species but also large sectors of marine life. With widespread degradation of biodiversity hotspots, such as coral reefs and rainforests, as well as other areas, the vast majority of these extinctions are thought to be undocumented, as the species are undiscovered at the time of their extinction, which goes unrecorded. The current rate of extinction of species is estimated at 100 to 1,000 times higher than natural background extinction rates and is increasing. During the past 100–200 years, biodiversity loss and species extinction have accelerated, to the point that most conservation biologists now believe that human activity has either produced a period of mass extinction, or is on the cusp of doing so. As such, after the "Big Five" mass extinctions, the Holocene extinction event has also been referred to as the sixth mass extinction or sixth extinction; given the recent recognition of the Capitanian mass extinction, the term seventh mass extinction has also been proposed for the Holocene extinction event.
The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.
Extinction is the termination of a taxon by the death of its last member. A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" after a period of apparent absence.
Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on natural and social sciences, and the practice of natural resource management.
Wildlife conservation refers to the practice of protecting wild species and their habitats in order to maintain healthy wildlife species or populations and to restore, protect or enhance natural ecosystems. Major threats to wildlife include habitat destruction, degradation, fragmentation, overexploitation, poaching, pollution, climate change, and the illegal wildlife trade. The IUCN estimates that 42,100 species of the ones assessed are at risk for extinction. Expanding to all existing species, a 2019 UN report on biodiversity put this estimate even higher at a million species. It is also being acknowledged that an increasing number of ecosystems on Earth containing endangered species are disappearing. To address these issues, there have been both national and international governmental efforts to preserve Earth's wildlife. Prominent conservation agreements include the 1973 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the 1992 Convention on Biological Diversity (CBD). There are also numerous nongovernmental organizations (NGO's) dedicated to conservation such as the Nature Conservancy, World Wildlife Fund, the Wild Animal Health Fund and Conservation International.
Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide levels exceeding 410 ppm. CO2 from the atmosphere is absorbed by the oceans. This produces carbonic acid which dissociates into a bicarbonate ion and a hydrogen ion. The presence of free hydrogen ions lowers the pH of the ocean, increasing acidity. Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.
The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between 237 Ma and 201.4 Ma. It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. The corresponding series of rock beds is known as the Upper Triassic. The Late Triassic is divided into the Carnian, Norian and Rhaetian ages.
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides. Other near-shore (neritic) zones can include mudflats, seagrass meadows, mangroves, rocky intertidal systems, salt marshes, coral reefs, lagoons. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web.
The giant Pacific octopus, also known as the North Pacific giant octopus, is a large marine cephalopod belonging to the genus Enteroctopus. Its spatial distribution includes the coastal North Pacific, along Mexico, The United States, Canada, Russia, Eastern China, Japan, and the Korean Peninsula. It can be found from the intertidal zone down to 2,000 m (6,600 ft), and is best adapted to cold, oxygen-rich water. It is arguably the largest octopus species.
There are several plausible pathways that could lead to an increased extinction risk from climate change. This is because every plant and animal species has evolved to exist within a certain ecological niche, and as climate change represents the long-term alteration of temperature and average weather patterns, it can push climatic conditions outside of the species' niche, which will ultimately render it extinct. Normally, species faced with changing conditions can either adapt in place through microevolution or move to another habitat with suitable conditions. However, the speed of recent climate change is so unprecedented, that even under "mid-range" scenarios of future warming, only 5% of current ectotherm locations are within 50 km of a place which could serve as an equally suitable habitat at the end of this century.
Climate change has adversely affected terrestrial and marine ecosystems, including tundras, mangroves, coral reefs, and caves. Increasing global temperature, more frequent occurrence of extreme weather, and rising sea level are examples of the most impactful effects of climate change. Possible consequences of these effects include species decline and extinction and overall significant loss of biodiversity, change within ecosystems, increased prevalence of invasive species, loss of habitats, forests converting from carbon sinks to carbon sources, ocean acidification, disruption of the water cycle, increased occurrence and severity of natural disasters like wildfires and flooding, and lasting effects on species adaptation.
There are many effects of climate change on oceans. One of the main ones is an increase in ocean temperatures. More frequent marine heatwaves are linked to this. The rising temperature contributes to a rise in sea levels. Other effects include ocean acidification, sea ice decline, increased ocean stratification and reductions in oxygen levels. Changes to ocean currents including a weakening of the Atlantic meridional overturning circulation are another important effect. All these changes have knock-on effects which disturb marine ecosystems. The main cause of these changes is climate change due to human emissions of greenhouse gases. Carbon dioxide and methane are examples of greenhouse gases. This leads to ocean warming, because the ocean takes up most of the additional heat in the climate system. The ocean absorbs some of the extra carbon dioxide in the atmosphere. This causes the pH value of the ocean to drop. Scientists estimate that the ocean absorbs about 25% of all human-caused CO2 emissions.
The climate across the Cretaceous–Paleogene boundary is very important to geologic time as it marks a catastrophic global extinction event. Numerous theories have been proposed as to why this extinction event happened including an asteroid known as the Chicxulub asteroid, volcanism, or sea level changes. While the mass extinction is well documented, there is much debate about the immediate and long-term climatic and environmental changes caused by the event. The terrestrial climates at this time are poorly known, which limits the understanding of environmentally driven changes in biodiversity that occurred before the Chicxulub crater impact. Oxygen isotopes across the K–T boundary suggest that oceanic temperatures fluctuated in the Late Cretaceous and through the boundary itself. Carbon isotope measurements of benthic foraminifera at the K–T boundary suggest rapid, repeated fluctuations in oceanic productivity in the 3 million years before the final extinction, and that productivity and ocean circulation ended abruptly for at least tens of thousands of years just after the boundary, indicating devastation of terrestrial and marine ecosystems. Some researchers suggest that climate change is the main connection between the impact and the extinction. The impact perturbed the climate system with long-term effects that were much worse than the immediate, direct consequences of the impact.
The Sixth Extinction: An Unnatural History is a 2014 non-fiction book written by Elizabeth Kolbert and published by Henry Holt and Company. The book argues that the Earth is in the midst of a modern, man-made, sixth extinction. In the book, Kolbert chronicles previous mass extinction events, and compares them to the accelerated, widespread extinctions during our present time. She also describes specific species extinguished by humans, as well as the ecologies surrounding prehistoric and near-present extinction events. The author received the Pulitzer Prize for General Non-Fiction for the book in 2015.
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary(K–T)extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kilograms also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.
Since the 19th century, a significant amount of research has been conducted on the Cretaceous–Paleogene extinction event, the mass extinction that ended the dinosaur-dominated Mesozoic Era and set the stage for the Age of Mammals, or Cenozoic Era. A chronology of this research is presented here.
Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, depending on whether the environmental degradation that leads to the loss is reversible through ecological restoration/ecological resilience or effectively permanent. The current global extinction, has resulted in a biodiversity crisis being driven by human activities which push beyond the planetary boundaries and so far has proven irreversible.
The poleward migration of coral species refers to the phenomenon brought on by rising sea temperatures, wherein corals are colonising cooler climates in an attempt to circumvent coral bleaching, rising sea levels and ocean acidification. In the age of Anthropocene, the changing global climate has disrupted fundamental natural processes and brought about observable changes in the submarine sphere. Whilst coral reefs are bleaching in tropical areas like the Great Barrier Reef, even more striking, and perhaps more alarming; is the growth of tropical coral species in temperate regions, which has taken place over the past decade. Coral reefs are frequently compared to the "canaries in the coal mine," who were used by miners as an indicator of air quality. In much the same way, "coral reefs are sensitive to environmental changes that could damage other habitats in the future," meaning they will be the first to visually exhibit the true implications of global warming on the natural world.
The Global Assessment Report on Biodiversity and Ecosystem Services is a report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, on the global state of biodiversity. A summary for policymakers was released on 6 May 2019. The report states that, due to human impact on the environment in the past half-century, the Earth's biodiversity has suffered a catastrophic decline unprecedented in human history, as an estimated 82 percent of wild mammal biomass has been lost. The report estimates that there are 8 million animal and plant species on Earth, with the majority represented by insects. Out of those 8 million species, 1 million are threatened with extinction, including 40 percent of amphibians, almost a third of reef-building corals, more than a third of marine mammals, and 10 percent of all insects.
References
- ↑ E.g. Julia Whitty (2007-04-30). "Animal Extinction - the greatest threat to mankind: By the end of the century half of all species will be extinct. Does that matter?". The Independent . Archived from the original on 2015-08-06. Retrieved 2010-05-20.
By the most conservative measure - based on the last century's recorded extinctions - the current rate of extinction is 100 times the background rate.
- ↑ Thackeray, J. Francis (1990). "Rates of Extinction in Marine Invertebrates: Further Comparison Between Background and Mass Extinctions". Paleobiology . Paleontological Society. 16 (1): 22–4. Bibcode:1990Pbio...16...22T. doi:10.1017/s0094837300009702. ISSN 1938-5331. JSTOR 2400930. S2CID 88902588.
- ↑ N.L. Gilinsky (1994). "Volatility and the Phanerozoic decline of background extinction intensity". Paleobiology. 20 (4): 445–458. Bibcode:1994Pbio...20..445G. doi:10.1017/S0094837300012926. JSTOR 2401228. S2CID 82320624.
- ↑ Raymond, H, Ward, P: “Hypoxia, Global Warming, and Terrestrial Late Permian Extinctions” Page 389–401. Science 15, 2005. http://www.sciencemag.org/cgi/content/full/308/5720/398
- ↑ popedadmin (2018-12-11). "What is Background Extinction Rate and How is it Calculated?". Population Education. Retrieved 2023-09-14.
- ↑ American Museum of Natural History, 1998. http://www.amnh.org/science/biodiversity/extinction/Intro/OngoingProcess.html Archived 2008-04-06 at the Wayback Machine
- ↑ Pimm, S.: “The Extinction Puzzle”, Project Syndicate, 2007. http://www.project-syndicate.org/commentary/pimm1
- ↑ May, R. Lawton, J. Stork, N: “Assessing Extinction Rates” Oxford University Press, 1995.
- ↑ Lawton, John H.; May, Robert McCredie (1995-01-01). Extinction Rates . Oxford University Press. ISBN 9780198548294.
- ↑ "End-Permian Extinction - Sam Noble Museum". 2015-05-04. Retrieved 2023-11-01.
- ↑ Riding, James B.; Fensome, Robert A.; Soyer-Gobillard, Marie-Odile; Medlin, Linda K. (2022-12-20). "A Review of the Dinoflagellates and Their Evolution from Fossils to Modern". Journal of Marine Science and Engineering. 11 (1): 1. doi: 10.3390/jmse11010001 . ISSN 2077-1312.
