Intro:
Sixty-five million years ago, some phenomenon triggered mass extinctions on the lands and in the oceans so profound that they define the geological boundary between the older Mesozoic Era, often called the "Age of Reptiles," and the modern Cenozoic Era, the "Age of Mammals."
On a finer scale, the extinctions define the boundary between the Cretaceous (geological symbol, "K"), and Tertiary ("T") periods. This mass extinction is usually referred to as the K-T extinctions. The dinosaurs became extinct during the K-T mass extinction. To examine how the K-T extinctions fit into a broader perspective, please see the
The cause of the K-T extinctions is one of the great mysteries in science, and many scientists have proposed theories to account for it. Theories span a vast spectrum of causes including: sea level change, supernova explosions, climate change, and on and on.
Beginning in the 1980s, two new theories became the topic of an intense scientific debate. They are the K-T impact extinction theory originated by the Nobelist physicist, Luis Alvarez, and his team, and the K-T Deccan Traps extinction theory, which, for short, is called volcano-greenhouse theory.
Details of the Impact Theory
In the mid-late 1970s, Luis Alvarez and his impact team began searching for the cause of the K-T extinctions.
His evidence of impact was enrichment of the chemical, iridium, in a thin layer of clay a few centimenters thick at the K-T boundary. His original theory held that a giant asteroid struck earth 65 million years ago, blasting so much dust into the atmosphere that it blocked out sunlight, and plunged earth into the blackness and cold of a sudden, short-duration, "impact winter."
According to Alvarez theory, the global blackout triggered extinctions among the plant kingdom, and then among herbivores that depended upon plants for food, and then among the carnivores that ate the herbivores.
Those smaller animals that could hide and hibernate until the sun came out again must have sruvived and formed the animals that there are today.
There is other evidence for this theory : there is a layer of iridium found on top of the fossils which can be found all over the world. this is important becouse there is a lot of iridium on asteroids while on earth it is only deep down inside the crater.
Details of the Volcano Theory:
Another less popular theory to explain the disappearance of the dinosaurs suggests that a drop in the oxygen levels in the lower atmosphere led to the gradual death of all kinds of species.
The possibility if a meteor strike as the cause of extinctions is discarded, something that most specialists agree on. There is no evidence of any meteor crater big enough or recent enough to be accountable for it; there are no “elements that are common extraterrestrially but less so on Earth, such as iridium, and no sign of a tsunami or other phenomena following the impact.” The extinctions where also very selective and occurred over a very long period of time. If a “one shot” catastrophe had been the cause it would have affected all species at the same time and in similar
That “prehistoric” whales had the jaw of a wolf (a fifty million year old wolf to be exact) and the ear of a whale. I think that all of our semiaquatic mammals play a big part in the evolution of land mammals to water mammals. Like at some point of say an otter’s life, nature told it to stop evolving so that it wouldn’t become completely marine, but semiaquatic as we named it. How did it know when to stop evolving? Was it changes in the environment? Or the need for survival? Which brings around another question, how did we go from a planet of just rock and magma, to a planet thriving with
“Bootycandy” is astonishing, shocking and appalling in a thought-provoking way that makes you question our society. O’Hara uses theatrical comedy as a gateway to share these stereotypes and struggles that minorities experience daily.
The disaster theory, Gould claims, is an example of good science. It has testable evidence and has an impact on studies in other fields of science, it develops further and explains why the extinction of dinosaurs occurred simultaneously with other events. This theory suggests that a large comet hit the Earth sixty five million years ago, causing the cloud of dust to rise into the sky and to block sunlight. As a result, world temperatures went down significantly, the ice age bega...
The question of what caused the extinction of megafauna during the Late Pleistocene period is one that archaeologists have struggled to answer for decades, but why should it matter? Discovering with certainty the cause of megafaunal extinction would simultaneously prove or disprove any of the proposed implications of each existing theory regarding this massive extinction.
The eradication of species numbers average at a toll close to one hundred percent of earths total living creatures. “It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct” (Sahney, and Benton 759). Not only where marine and terrestrial species effected but this catastrophic event is the only recogni...
We use dinosaurs to represent the changes in nature that have occurred throughout time. Studies found that although the “oldest rock did not show evidence of life, the progression of plant and animal life that changed in recognizable intervals, from ancient life, age of reptiles to the age of mammals” (Dino Nature Metaphor, slide 6), measured the age of the earth. When we think of dinosaurs in relation to nature, we think of that very powerful force that controls the cycle of life. Nature was able to yield such magnificent ferocious creatures that walked the earth and then take them back when they served nature’s purpose. Dinosaurs fit perfectly in nature’s constant
The concept of transitional species is an important and complex notion in evolutionary biology. To begin with, there is no such thing as transitional species since all living things were always evolving in the past, not stopping at one stage or another, and they will continue to evolve in the future. In terms of evolutionary biology, we use the concept of transitional species as a way to dim ambiguity. Much like the use of the Linnean taxonomic system of species, we come up with concepts like transitional species to organize and classify species in order to understand their evolutionary roots and how those species changed through life’s history to become what they are today. “In the same way that the concept of species can be provisionally meaningful to describe organisms at a single point in time, the concept of transitional species can be provisionally meaningful to describe organisms over a length of time, usually quite a long time, such as hundreds of thousands or millions of years” (111). Though it can be difficult to distinguish what can be considered an ancestral species from another, the fossil record can show us how species change through time as they develop ways to adapt to stresses found in their environments. “In the modern sense, organisms or fossils that show intermediate stages between ancestral and that of the current state are referred to as transitional species” (222). The concept of transitional species is, in essence, fairly straight forward. This paper will outline the concept of transitional (or sometimes termed intermediate) species and the latter’s role in evolutionary biology, as well as go in depth about several common transitional species: Tiktaalik, an animal at the cusp between life in the water and ...
Throughout Earth’s history there have been many changes. These changes have consisted of temperature fluctuations, atmospheric differentiations, extinctions of various plant and animal life, etc. Over time everything seems to have evolved in some way form or fashion. However, the Permian Era extinction was different from all the rest. This extinction affected every form of life, but especially the marine life. Researchers have stated that 93-97% of all Earths species went extinct during this period of time. This essay will explain how a once blossoming progressive era turned into Earths most catastrophic event.
...asted about a million years. The eruption was not violent compared to others, but it was able to send ash as high as the stratosphere. So another theory is that shifting of the tectonic plates caused the Deccan Traps to erupt, causing the release of massive amounts of carbon dioxide out of the earths crust. This went on to create a global greenhouse effect that cooked the planet. This along with climate change from continental drift could have caused the K-T event. Paleontologist Richard Cowen believes the evidence of an asteroid impact is so strong that there is no point to explain that evidence as solely volcanic effects. We should concentrate on the fact that the K-T boundary coincided with two different, yet very dramatic events.
living on earth disappeared. So how did these dominant creatures just die off? Was it a
The K-T Extinction occurred 65 million years ago. Many species perished in that extinction. Today evidence for this extinction can be seen in the fossil record. Biological, botanical and geological evidence at the Cretaceous – Tertiary Boundary show that some enormous event occurred that caused mass extinction of life on the Earth. Controversy about the cause of the K-T extinction exists with two main theories currently being in favour. One theory is called Intrinsic Gradualism and believes the cause of the K-T Extinction was a slow and gradual Earth generated event, caused by intense volcanic activity and the effect of plate tectonics. The second theory is known as Extrinsic Catastrophism and proposes that the K-T Extinction was caused by a sudden and violent catastrophic event such as the Earth being struck by a meteor or asteroid. The K-T Extinction supports the concept of Punctuated Equilibrium in evolution because surviving species evolved and others were exterminated. This creates the stepladder effect of evolution seen in the fossil record .
Narrative Therapy was developed to help people separate themselves from their problems. The idea is that this will help the person use the skills that they already possess to minimize the problems that exist in their everyday lives. The Narrative Therapy approach was developed by Social Workers Michael White (Australia) and David Epston (New Zealand) during the 1970s-1980s. “White proclaimed is work to be exclusively that of ‘rich story development’ “(Gallant).
Earth has gone through five fully major extinctions before. We currently are in the process of Earth’s sixth mass extinction. This mass extinction is closely related in severity to the extinction of the dinosaurs. Earth’s extinctions are broken into three different areas. The first area was the large number of animals caught by hunter-gathers. The discovery of agriculture led to the second area of extinction, wildlife habitats. These wildlife habitats were destroyed due to humans starting to stay in one area.
Almost 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species went extinct (Beaz). Although the cause of this mass extinction is debatable, many speculate that global warming was the killer. Because Pangea was breaking up into Laurasia and Gondwanaland, there was widespread volcanic activity caused by the rifting, increasing atmospheric carbon dioxide. The massive release of this greenhouse gas increased global air temperatures and resulted in acidified oceans along with rising sea levels. If this is the case, the life in the ocean would have died at a significant rate. Many families of brachiopods, gastropods, bivalves, and marine reptiles became extinct (Rafferty). An important trace fossil known as the phylloceratid ammonoid was able to survive, and they gave rise to the explosive radiation of cephalopods later in the Jurassic Period, as well as evolved into many different forms during the later Cretaceous (End Triassic Extinction). This extinction event ranks fourth in severity of the five major extinction events over geologic history