The Common Pattern Of Alternating Extinctions And Radiations

“A minority disputes this theory, arguing that other events-such as volcanic eruptions, sea-level changes or a series of impacts-were to blame for the spectacular loss of species that occurred at the transition between the Cretaceous and Tertiary periods…”

Since the beginning of time our Earth has experienced many changes, these changes affected Australian biota whether it be in a positive or negative way. The study of Australian fossils contributes to the development of understanding the evolution of species in Australia in many different ways, such as seeing changes in physical appearance of species, and possible reasons why the species evolved into what they did, when and why a certain species may have become extinct and evidence/proof of theories such as natural selection. Each of these goes hand in hand and helps us find out what our Earth would have been like millions of years ago.

8. The periods in which there were mass extinctions are Permian – volcanic eruptions which spewed lava and put CO2 into the air which warmed the climate an estimated 6 degrees Celsius. The resulting of oxygen deficiency. And Cretaceous – asteroid or comet

Chapter Four looks at the dust created by the Cretaceous-Paleogene extinction event, which resulted in many species--excluding the ammonites--dying out. This illustrates that the advantageous nature of some traits can be altered by a single moment.

The main dinosaurs that died off were Sauropod dinosaurs, long necked, four legged dinosaurs, and stegosauridae, class holding Stegosaurus. Other species that died include ammonites, similar to the living animals called nautilus, many marine reptiles, and bivalves, relatable to modern mollusca. Not much is known about this extinction. It is mainly linked to climate change. So far, no connection to volcanic activity or an asteroid has been made. This extinction gave way to the Cretaceous Period.

Assess the different hypotheses put forward for the mass extinctions at the end of the Permian and Cretaceous (KT) Periods.

<b>Introduction</b><br>Think of a world which existed 290 million years ago. As you look out over the terane in front of you, you think that you are on an alien planet. You see volcanoes spewing ash and lava. Beside them is the ocean which is swarming with many different species of echinoderms, bryozoans and brachiopods. As you look down onto the sea floor you are amazed at the countless number of starfish and urchins. Some animals leave you can't even describe and you have no idea even what phylum they belong to. This is a world at its height in diversity of oceanic species. Millions of wonderous species existed at this time in the ocean and most of them will never appear again in earth's history. In the geologic time scale, a million

Environmental conditions are sometimes appropriate for the evolution of numerous species from a common ancestor. Evolutionary, or adaptive, radiations happen when a large number of species descend from one lineage. This phenomenon usually occurs when a population of one species colonizes an area with many available ecological niches and when the rate of speciation is greater than the rate of extinction in a given area. Adaptive radiations have historically taken place after mass extinctions and on newly formed island archipelagos, because these incidences create conditions where new species can fill open ecological niches. Unlike the mainland, ecological niches are available on new island systems. These island species adapt to new environments

The Permian mass extinction, that struck about 250 million years ago, caused a mass extinction of reef and shallow water communities. Groups that lived on the seafloor and filtered organic material from the water for nourishment suffered the greatest extinction. Those include corals, shelled in-vertebrates, and a variety of sea lilies. Others marine groups includes trilobites, zooplankton and snails. Even though these species died in the water, living organisms on land were not much better off. Terrestrial vertebrates and insects both experienced a big loss in each of their groups. Also suffering a big loss was the insect family due to the lack of plant life and food. Seventy Eight percent of reptiles became extinct and sixty seven percent of the amphibian family became extinct during this time period.

The cretaceous-tertiary (KT) boundary extinction happened approximately sixty five million years ago. Sixty to eighty percent of all living species became extinct at this boundary (Raup 1988). The KT extinction was indeed a mass extinction event. Mass extinctions are periods in Earth's history when extremely large numbers of species die out simultaneously or within a limited time frame. The most severe mass extinction ever occurred at the end of the Permian period when 96% of all species died out. The K-T mass extinction obliterated almost all the large vertebrates on Earth, on land, at sea, and in the air (all dinosaurs, plesiosaurs, mosasaurs, and pterosaurs) suddenly became extinct at the end of the Cretaceous Period. At the same time, most

Foraminifers are better known for their spectacular fossil record than for their variety or abundance in modern marine environments. They, however, constitute the most diverse group of shelled microorganisms in modern ocean The facts that benthic Foraminifera fossilize well, and may constitute the only tracers of ancient benthic environments, provide an additional reason to investigate the ecology of both epifaunal and infaunal components of the assemblage (Sen Gupta, 2007).

Ever since the history of Earth has been studied using fossil records, extinctions have always been the object of fascination and interest, particularly the mass extinctions that occurred throughout Earth's history. A mass extinction can be caused by disruptive global environmental changes, where large numbers of species have become extinct (Urry et al. 2008). There have been five major extinctions documented based on fossil records over the past 500 million years, but the Cretaceous (KT boundary extinction – a name that meant it began the Tertiary era) extinction caught a lot of

There have been five well known extinctions on this earth. The one most well known is the mass extinction that ended the dinosaurs. Mass extinction is often described as the elimination of a large number of species in a short period of time. Despite what many think, the elimination of species is almost commonplace at this point. The Earth is currently in the middle of a sixth mass extinction, and it’s been caused by the human race.

However, such mass extinction opens up speciation – when new species are developed. After the K-Pg extinction, new groups of organisms were on the rise. Giant boid snakes (12 – 15 meters) began appearing on land and the teleost fish (diverse class of ray-finned fish) filled marine niches left vacant. Most significantly, “Paleocene mammals would spread and evolve into the many ecological niches left open by the extinction of the dinosaurs,” (“Cretaceous: Extinction of the Dinosaurs”).

These techniques led to the discovery of the boundary between the two eras. A single thin layer of clay found within predominantly limestone rocks established this. By comparing the marine life found in, above, and below the clay, the marine life, like the dinosaurs, had been terribly affected by the extinction event. The percentage of life in the upper layers was dramatically lower than that in the lower. This was far more compelling than what was suggested by dinosaur’s fossils.