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The era of greyhound racing in the U. See how people have imagined life on Mars through history. A Smithsonian exhibit in the Sant Ocean Hall shows how salmon for centuries have shaped a way of life for Native Americans living in the Pacific Northwest. Recent improvements in genetic engineering have raised questions about bringing extinct species back to life. Since Dolly the sheep was cloned in , scientists know it is possible to create an organism from the DNA in a single cell.
Stored in museum collections throughout the world are specimens of extinct animals containing DNA. The idea of using DNA to revive extinct species and repopulating them is controversial. How would we choose which ones? How would they impact species still on Earth? Skip to main content. Smithsonian Institution. Extinction Over Time.
Helena olive tree -- extinct from logging and plantations Extinction Rates Recent studies estimate about eight million species on Earth, of which at least 15, are threatened with extinction.
Five Mass Extinctions At five other times in the past, rates of extinction have soared. Preventing Extinction The science of conservation biology focuses on managing ecosystems to prevent species from going extinct. Reversing Extinction Recent improvements in genetic engineering have raised questions about bringing extinct species back to life. Related Videos. Mass Extinction - Solving the Dinosaur Mystery.
Human Impacts and Extinction of Freshwater Snails. Mass Extinction of Large Dinosaurs and More. Bird Extinctions in Recent Geologic Time. Freshwater Snails and Ecosystems. However, there have been dramatic increases in extinction rates since humans have become Earth's dominant large animal and the cause of global environmental change. At least five major mass extinctions have probably occurred in the geologic past.
The mass extinction occurred in 2 phases; at the beginning and in the middle of Hirnantian Age. In the first phase of extinction, changes in nutrient cycling as a result of glacially-forced regression were thought to be responsible. Stagnation of oceanic circulation and post-glacial temperature and sea level rise were the main cause of the second phase of extinction. Meanwhile, both extinction events were thought to be stimulated by the rapid change in climate [1].
It is believed that a gigantic volcanic eruption triggered global warming through the release of carbon dioxide and methane. This mass extinction first started in the deep ocean area, and then moved up to the upper layers of ocean, killing almost all living creatures. Invertebrates are perhaps the most diverse group of marine organisms, and yet are being lost in the highest numbers.
At the beginning of the Cambrian era about million years ago , numerous animals from this phyla propagated during an evolutionary radiation, but most of them are now extinct. The extinct phyla from that period are known from the Burgess Shale of British Columbia. It is estimated that since the beginning of life on Earth, an average of 0.
Current evidence suggests that at least species have become globally extinct in the past years [4]. Extinction ratios in the past centuries are times higher, which is attributed to human activity. The vast majority of extinctions are terrestrial species.
There is unequivocal evidence for the extinction of 12 marine species, comprising three mammals, five seabirds and four gastropods [5]. An additional three bird and mammal species are listed as extinct by the World Conservation Union IUCN Red List [4] , and a recent survey has uncovered evidence to suggest the global extinction in the wild of a further six species comprising two fishes, two corals and two algae [6].
The extinction rate in the marine environment is thus probably more than 10 times lower than in the terrestrial environment. However, the marine figures are not very reliable. We don't really know how many marine species exist. About , marine species are known, while estimates of the total number of marine species range between , and 2 million [3]. There is uncertainty about taxonomic status and also in defining when the last individual has gone [5]. However, there can be no doubt that currently, extinction is happening at an alarming rate and faster than it did prior to [7].
Previous mass extinctions evident in the geological record are thought to have been brought about mainly by massive climatic or environmental shifts. Mass extinctions as a direct consequence of the activities of a single species are unprecedented in geological history. While there are no doubts about the global decline of marine biodiversity , this is less apparent on a local scale. Studies of local marine habitats do not provide clear evidence of a reduction in species richness [8] [9] [10].
Although these studies may not provide a complete representative picture, they provide a strong indication that changes in biodiversity on a global scale are not automatically reflected on a local scale.
The intensive exploitation of marine organisms has a short history in comparison with the terrestrial organisms, only commencing in the last few hundred years. Initially, marine animals were not obviously threatened by the wave of extinction that land species were subjected to. However, marine species have been put under great pressure since humans became able to travel over the sea. In this short period, human exploitation of marine resources has been a major factor of extinction, both through direct mortality of target species and multiple collateral effects on non-target species bycatch.
Fisheries are also indirectly responsible for biodiversity loss and ecosystem disturbance by abandoning huge amounts of derelict fishing gear in the ocean, which is deadly to many marine top predator species.
See also the article Overexploitation. Biological, physical and chemical factors in most ecosystems are tightly intertwined. Hence changes in one of these factors can result in changes of others. Exploitation of habitat can therefore profoundly influence many components of a system.
Examples of habitat destruction are:. Recent climate change such as global warming has increased local water temperatures beyond the suitable range of many species. Such changes have made highly productive areas, such as up-welling regions, become less productive due to changes in the food web. Lower primary production supports a lower biomass of primary consumers. In the oceans, krill are major primary consumers that support many important ecosystems.
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