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Research Paper Example on Mass Extinction

7 pages
1756 words
Boston College
Type of paper: 
Research paper
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Major and minor mass extinctions have happened in the history of our planet. Ideally, mass extinction involves massive decrease or deaths of a large number of species in the ecosystem within a relatively short period. Over the last 500 million years, many mass extinctions occurred and among the documented extinctions include five major mass extinctions and four minor extinctions. The five major mass extinctions are Ordovician-Silurian extinction events, late Devonian extinction, Permian-Triassic extinction, Triassic-Jurassic extinction, and Cretaceous-Paleogene extinction event. The four minor extinctions are Paleoproterozoic, Sturtian, Marinoan, and Ediacaran extinction. These mass extinctions are believed to be caused by catastrophic global events such as global warming, falling of sea-levels, oceanic overturn, flood basalt events among other causes. Mass extinction has affected the worlds biodiversity and killing of valuable species in the ecosystem. Additionally, mass extinction accelerated the evolution of life on earth. The paper aims at analyzing some of the major and minor extinction events in the world, their causes and the effects they had on the ecosystem.

Major and Minor Extinction Events

Five Major Mass Extinctions

Ordovician-Silurian Extinction Events

This is one of the largest extinction events because it led to the extinction of a high number of genera species. This occurred around 440 million years ago and was characterized by loss of marine species such as one-third of bryozoan and brachiopod families and death of graptolites, trilobites, and conodonts groups. The possible causes of this extinction event are associated with glaciation effect, gamma ray burst, metal poisoning, and weathering and volcanism. This mass extinction significantly affected marine diversity due to loss of a large number of taxa in the earth within a very period. However, it was ended by melting of glaziers that caused the rise of sea levels (Hull and Simon 1-42).

Late Devonian Extinction

This is another major mass extinction event that resulted in massive loss of biodiversity. The incident happened around 370 years ago and was characterized by loss of approximately 75% of animal species during the Devonian period and roughly 20% of Devonian animals families. Animals died due to widespread anoxic sedimentation which caused the limited supply of oxygen. Scientists believed that these mass extinctions were caused by effects of carbon dioxide, plant evolution, bolide impact, global cooling, and oceanic volcanism. The biological impact of these events includes the collapse of the reef system that killed shallow warm-water organisms (Hull and Simon 1-42). Moreover, the event led to the loss of vital invertebrates families hence resulting in profound loss of ecosystem diversity.

Permian-Triassic Extinction Event

This is another mass extinction event that occurred 250 million years ago. It is recognized as the most severe mass extinction event because it caused the death of over 95% of marine species, extinction of insects, and killing over 65% of terrestrial vertebrate species. Similarly, it caused the destruction of over 80% of all genera and 60% of all families. This mass extinction event is believed to be caused by microbes, supercontinent Pangaea, hydrogen sulfide emissions, anoxia or methane hydrate gasification (Hull and Simon 1-42). However, the ecosystem was later recovered in the form of disaster taxa which was opportunistic organisms. These organisms took advantage of devastated ecosystems and massively reproduced.

Triassic-Jurassic Extinction Event

This extinction event occurred about 200 million years ago, and it marked the boundary between the periods of Jurassic and Triassic. This incident led to the death of land and marine organisms such as all class of archosaurs on the land and whole class of conodonts in the seas. Amphibians animals are the most affected group that became extinct. Among the primary causes of this event include impacts of asteroids, volcanic eruptions, oceanic acidification, fluctuations of sea-level, and climate change. The primary consequences are the reduction of earth species by half which resulted in the vacation of terrestrial ecological niches (Hull and Simon 1-42). It paved the way for the dominance of dinosaurs in the ecosystem.

Cretaceous-Paleogene Extinction Event

This is the last major mass extinction event that occurred approximately 66 million years ago. It caused the extinction of over three-quarters population of animal and plant species on earth. Among the most affected species are tetrapods which were massively killed. This event was also characterized by persistent impact winter that affected the photosynthesis processes of plants. The extinction patterns occurred for marine invertebrates, fish, archosaurs, and amphibians. The leading causes of this events are effects of asteroids, Deccan Traps flood basalts, and Maastrichtian sea-level regression. However, this extinction marked the evolution of mammals to replace dinosaurs while other organisms underwent significant radiations (Hull and Simon 1-42).

Nevertheless, there is a notion that the earth is now undergoing the sixth mass extinction event. The leading cause of this event is human activities such as the killing of mastodons until they became extinct, destroying carrier pigeon, and killing other endangered animal species. The transportation of invasive species throughout the world led to the killing of native species. Pollution is another factor that contributes to organisms because of effects of fossil fuels on temperature levels and weather patterns. Lastly, massive deforestation, dumping of chemicals to seas and rivers, and exploitation of natural resources slowly caused the extinction of many animals, plants, and resources.

Minor Extinctions

Other than the major mass extinction events, several minor extinctions affected several species of animals and plants. The first extinction occurred during a Paleoproterozoic era in about 700 million years ago where stromatolites declined in diversity and abundance. The reason behind this decline is the growth of herbivorous eukaryotes that massively fed on stromatolites hence destroying them. The second relatively significant extinction occurred during the era of Sturtian glaciation which was massive. This happened around 700 million years ago and affected a large number of species especially insects (Wooldridge 2401-2423). The ice sheets made small organisms lack oxygen hence causing mass deaths.

Another event of mass extinction was Marinoan glaciation that happened about 640 million years ago. During the Cryogenian period, a significant amount of snow covered the entire planet. Unlike Sturtian glaciation, this event was most notable and persisted for a long time causing substantial environmental impacts and killing of animal and plant species. The last relatively massive mass extinction occurred during the era of Ediacaran destruction. This happened around 540 million years ago and was characterized by large-scale burrowing activity and diversity among many organisms. Among the organisms that were killed include acritarchs, Ediacaran biota, and other calcifying organisms. However, other microorganisms managed to survive this high scale glaciation (Wooldridge 2401-2423).

Causes of Mass Extinction

Asteroid Impact

This evidence argued that asteroids are one of the greatest cause of mass extinction globally. According to this argument, asteroids caused the disappearance of the dinosaurs around 60 million years ago. Ideally, the fall of massive earth-crossing asteroid creates a rock in the atmosphere, and its clouds of dust are trapped in the stratosphere for an extended period. It later results in the darkness that inhibits photosynthesis and breathing of plants thus contributing to their extinction.

Similarly, the fall of asteroids into a glacier leads to its melting and breaking apart thus blocking the natural cooling and cooling cycle of oceans and eventually leading to rising of sea levels. Additionally, large asteroids emit a large number of remains to the atmosphere which blocks sunlight from reaching the earth thus denying plants and animals the required sunlight for growth (Benton, 580-585). Ultimately, many species will freeze and die especially if the debris takes a long time to disperse.


Various major diseases in the past contributed to the mass extinction of species in the ecosystem. These diseases are caused by viruses, fungi or bacteria and can attack and wipe out entire family or class of specific species. For instance, male-killing bacteria was common in the past, and it was capable of hitchhiking from parent to offspring while continuously killing particular species until it completely wipes out.

The most common cause of mass extinction was infectious diseases and contributed to over 15% of all species killings. The most affected group is amphibians which was almost entirely wiped out by infectious diseases. A large number of Dinosaurs died due to infection of Leishmania and malaria (Benton, 580-585). These diseases were brought about by fluctuating temperatures at the surface of the ocean. Similarly, dinosaurs were wiped out by disease-carrying insects such as intestinal worms, protozoa, and blood-sucking flies. They weakened the immune system of dinosaurs and lastly killed millions of them within a short period.

Gamma Rays

Gamma rays in the past were released by during supernova events by the stars or during the merging process of binary neutron stars. The energy produced by these processes is more powerful than suns energy and can be harmful to the species in the ecosystem. This is because it contains highly penetrating rays that can tear apart animals skin or kill cells and DNA in their bodies.

Scientist argued that the gamma rays were prevalent many years ago and were responsible for massive deaths of a large number of species that existed. For example, they believed that the primary cause of Ordovician mass extinction was bursting of gamma rays which damaged the ozone layer. Species were then exposed to UV rays that destroyed them entirely. Moreover, gamma rays may result in global glaciation and cooling which freezes many species for many years until they become extinct (Benton, 580-585).

Global Anoxia

Global anoxia is caused by significant reductions in oxygen levels especially in sea water, anoxic waters or underground water. It is believed that global anoxia was the primary cause of Devonian mass extinction where 75% of animals were wiped out. During the late Permian, all the oceans in the world become anoxic at both low and high paleo-latitudes. This significantly affected marine organism who massively died to due lack of oxygen.

Similarly, the Cenomanian era was characterized by volcanic eruptions, and the volcanic ash found their way to the oceans, in turn, it flooded the water with micro-nutrient iron which fertilized surface waters. After a short period, the oxygen levels in deep waters became depleted because of global phytoplanktonic bloom. Another theory argues that toxic elements from basaltic volcanism consumed oxygen in several oceans hence causing the Permian-Triassic mass extinction. During Phanerozoic mass extinctions, the algal blooms produced specific organic material that used all the oxygen in the oceans leading to the death of marine organisms (Benton, 580-585).

Global Cooling and Glaciation

Scientist found that four significant glaciations had preceded the era of Cambrian explosion. The most destructive worldwide ice age was the Ordovician which resulted in massive deaths of species in the ecosystem. Ideally, the 5-major mass extinction was associated with global cooling which caused the level of water to rise and formation of glaciation. The composition of glaci...

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