Life consists of many different eras and stages where life developed and evolved. In fact, life as we know would not exist if we had not evolved over many time epochs. Through numerous mass extinctions, life has persevered. While life progressed in all the different eras, the most important ones were the Paleozoic and Cambrian Eras. 541 million years ago, the most important revolutionary event in the history of life occurred. This event, later named the Cambrian Explosion, began in the Paleozoic era, and “refers to the sudden appearance in the fossil record of complex animals with mineralized skeletal remains” (Royal Ontario Museum); the Cambrian Explosion lasted 53 million years. In the fossil record, the marks where worms made horizontal Large amounts of reef building organisms died out. Because ofany hypothesize that this was due to short-term depletion of oxygen. This depletion could have been caused by an upwelling of cooler water from deep ocean areas. ‘This upwelling eventually resulted in a variety of marine environments ranging from the deep ocean to the shallow coastal zones. Scientists hypothesize that this increase in available ecological niches set the stage for the abrupt radiation in life forms commonly called the “Cambrian Explosion”(Bagley). “It was once thought that Cambrian rocks contained the first and oldest fossil animals, but these are now found in the earlier Ediacaran (Vendian) strata” (Waggner/Collins). While the Cambrian rocks did not have the first fossils, they did have the most variety of fossils for their time. Among the animals that evolved during this period were the: chordates, brachiopods, and They examined how much iron, molybdenum and other metals were in the environments. “These proxies seemed to indicate that oxygen concentrations in the oceans rose in several steps, approaching today's sea-surface concentrations at the start of the Cambrian, around 541 million years ago — just before more-modern animals suddenly appeared and diversified. This supported the idea of oxygen as a key trigger for the evolutionary explosion ”(Fox). Researchers conclude that the earth was covered with ice, and large glaciers prior to the Cambrian Explosion. This is also referred to as Snowball Earth. The sheet of ice and large glaciers would have hindered the amount of sunlight the algae and cyanobacterial mats would receive, as well as limit the number of evolutionary possibilities in the sea. Following this line of thought, it would be responsible to assume that large expanses would begin to be capable of life once the glaciers began to
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
(Quimby 6). Between this time period, in 6000 B.C., the basins of the upper Great Lakes became entirely ice free
In conclusion, we are successfully able to recreate the ecosystem of two unknown species from the few pieces of information provided to us. It is important to understand the importance of extinct fossils as they contribute to our understanding of life in the past and hold vital information to how the world was back then.
The cause of the Second Punic War is an issue of some great debate. Polybius is someone who gives a very good account of the events that led to the war, blaming the Carthaginians for causing the war. This raises a very large question on the part of Polybius. Was he right to assume that it was the actions of Hannibal and the Carthaginians that led to the war, or was there some other underlying events that took place the actually caused the Second Punic War? It is my belief that Polybius assumption was correct in a sense. However it seems that actions of the Roman state played a large part in provoking the war.
They ruled the world before the time of the dinosaurs, from the Cambrian Period to the
The major composition of the ocean chemistry that is affected by atmospheric CO2 are understood for the most part and can be calculated accurately. However there is much uncertainty of the biological effects caused by ocean acidification and how it will vary amongst organisms; some may cope better than others. Even though the research on ocean acidification is still very young, there is already evidence of biological impacts due to changes in the chemistry of the ocean. The greatest evidence of the impactions of ocean acidification on marine ecosystems can be seen in experiments on calcifying organisms. When seawater is acidified to various amounts the formation and dissolution of calcium carbonate shells and skeletons in marine organisms such as reef-building corals, oysters and mussels, and phytoplankton and zooplankton which for the base for marine food webs (“Ocean Acidification: A National Strategy…”,
...nder, C., Tsai, C., Wu, P., Speer, B. R., Rieboldt, S., & Smith, D. (1998/1999/2002). The permian period. Informally published manuscript, Biology 1B project for Section 115, University of California Museum of Paleontology, CA, Retrieved from http://www.ucmp.berkely.edu/permian/permian.php
Han, J., Zhang, Z. F., & Liu, J. N. (2008). A preliminary note on the dispersal of the Cambrian Burgess Shale-type faunas. Gondwana Research, (1), 269-276. doi:10.1016/j.gr.2007.09.001
There are several theories about how the Cambrian Explosion started. There were major changes in marine environments and chemistry from the late Precambrian into the Cambrian, and these also may have impacted the rise of mineralized skeletons among previously soft-bodied organisms. One theory as to what happened is that oxygen in the atmosphere, with the contribution of photosy...
Several mass extinctions have occurred during the Earth’s history. The Cretaceous – Tertiary Boundary (K-T) Extinction caused the loss of at least three-quarters of all species known at that time including the dinosaurs. The cause of this mass extinction is a controversial subject among scientists but the fossil evidence of it’s occurrence is abundant.
...deposition and blanket of sediment kept the organisms compressed with little exposure to oxygen for decay. If life was predominately terrestrial during the Cambrian, the organisms predictably would have been left untouched after death long enough to decay, preventing the fine preservation of many soft-bodied organisms. Fortunately enough, it was marine life that dominated the Cambrian (Scott, et al., 2000).
- - -. The Rise of Life on Earth. New York: New Directions, 1991. Print.
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
One argument that supports the panspermia theory is the emergence of life soon after the heavy bombardment period of earth, between 4 and 3.8 billion years ago. During this period, researchers believe the Earth endured an extended and very powerful series of meteor showers. However, the earliest evidence for life on Earth suggests it was present some 3.83 billi...
This essay discusses the evolution of amphibians. Amphibians are classified into three orders (anura, caudata and apoda) and are in the superclass tetrapoda (Kolesova, et el, 2007). The Apoda is comprised of organisms with no legs, and these organisms normally live in barrows. Tretrapods are comprised of vertebrates with four limbs; and examples of tetrapods are reptiles and amphibians (Kolesova, et el, 2007). Tetrapods were the earliest vertebrates to be able to walk on land and that was during the Devonian period about 360-370 million years ago (Kolesova, et el, 2007). Before the existence of amphibians almost all vertebrates lived in water (Kolesova, et el, 2007).