| 560-540
MILLION YEARS AGO |
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Closer to 542 million years ago, there was another explosion of multi-celled animal lifeforms of enormous variety in the oceans, inland seas and lakes of the Earth. The development of specialised appendages that permitted reasonably rapid mobility in the ocean to help gather food more efficiently and, more importantly, escape other predators probably played an important role in the sudden burst of animal life at this time. (1)
As animals moved closer to the surface of the oceans, the UV radiation may have assisted in creating many more mutations, of which the worse kinds were weeded out by natural selection and the better ones survived. It is believed this led to a bewildering array of animal species with different and unusual defence mechanisms, more sensitive eyes in greater numbers to observe the presence of other animals in multiple directions, better means of gathering food from the ocean floor, and better appendages and body shapes for swimming through the oceans.
Dr Jean-Bernard Caron, a palaeontologist from the Royal Ontario Museum, is of the view that predators were probably the single biggest factor in pushing animals at this time to diversify into many varied forms. He said:
'It is during the Cambrian, starts with animals with legs and eyes, swimming. This didn't exist before. And this evolved very quickly at the beginning of the Cambrian.
'We think that this evolution occurred relatively quickly because..you find organisms that may have had some kind of different defence mechanism which has got to be response to higher predatory levels.'
Possibly the oldest fossil of an invertebrate found in South Australia has been dated to around 560 million years ago.
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| 530
MILLION YEARS AGO |
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Ancient fish with backbones (for greater mobility and as an effective internal protection for the nervous system and other vital organs) and hard-shelled organisms (for greater external protection from the ravages of physical attack from predators) proliferated in the seas. (2)
About 550 million years ago, marine invertebrates suddenly increased in numbers and types, including Trilobites and Brachiopods. Source: Reader 1986, p.53.
This was also the time for the emergence of the highly successful ocean floor scavenger and hard-shelled organism known as the Trilobites. Hard shells are formed by absorbing calcium carbonate and other minerals from the ocean to help give them their legendary strength. Because of their hardness, trilobites have been found fossilised in greater numbers and in a variety of different species. Scientists have identified over 50,000 different trilobite species. Many more species are expected to be found locked away in the rocks of northern Africa and other places.
And it isn't just the hard-shelled exo-skeleton that gave these trilobite species their evolutionary advantage. Most species also had the power of sight to observe the environment in incredible stereoscopic detail. While some trilobites made full use of the ocean floor in deeper waters without the need for sensitive eyes, many other species adapted to shallow seas and coastal regions where their eyes could develop and make full use of the sunlight penetrating the water to paint a realistic view of the watery environment they lived in.
Trilobites were not afraid of colder waters. In fact, the biggest trilobites measuring up to a metre long have been found in places along the African coastline. At around this time, the African continent was positioned over the South Pole.
Earth in the Late Cambrian era around 514 million years ago. Image © 1997 C.R. Scotese is available from http://www.geologie.uni-stuttgart.de/down/maps2/pl2.jpg.
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NOTES
- Other scientists suggest the reason for the sudden burst in the diversity of animal life could be the result of the small DNA molecules used for reproduction were not tightly packed into chromosomes and this may have increased the chances of genetic mutations from occurring, especially if the transferring of sperm to eggs was not direct via sex or were exposed to greater amounts of UV radiation near the surface of the water as the animals tried to escape predators as well as reach for the food supply. This theory is known as the genomic hypothesis.
NOTE: Animals can escape predators by going deeper in the oceans to below 300 metres and up to 1.5 kilometres in depth. The ones able to do this successfully are the least likely to experience genetic mutations from UV radiation and consequently are able to maintain their ancient and bizarre biological forms to this very day. Any mutations leading to possible changes in biological shape and function probably only occur once every 250 million years. Compare this situation to the animals living near the surface and above the water and we quickly understand why land animals have changed so significantly in a period of less than 250 million years.
Then there is another view held by scientists that the early oceans were devoid of competitors and there was plenty of food by way of bacteria and algae, so life evolved into any viable variant it could find. However, it is a fact of life that animals do not like to change unless they are forced to or can see a definite advantage in the change. Therefore, the latter theory known as the ecological theory may only play a small role in the Cambrian explosion of life.
- The idea of life evolving and making continuous random and tiny increments in evolutionary improvement over time was first proposed by Charles Darwin as he studied the animals of the Galapagos Islands in the 18th century.
It is true that regular and tiny changes do occur on a microscopic level (which is why all living things eventually show signs of aging over time). However, on a macroscopic level, evolution normally makes evolutionary jumps due to the changes made in the active sections of the genetic information stored in the macromolecule known as Deoxyribonucleic Acid (DNA). Furthermore, the evolutionary jumps do not always result in an improvement. Nevertheless, Darwin's theory of evolution is believed to be essentially correct.
NOTE: Evolution is not just controlled by our genes, but also by our environment. You need the environment to influence the genes just as much as you need the genes to influence our environment. For example, the extension in the lifespan of many people in developed countries cannot be explained entirely by our genes. Something else must be influencing this, and this has to be the environment. But this is not so much an issue of evolution unless people in developed countries intermingle sufficiently to create new genetic variants of one another which promotes this longer lifespan without the influence of the environment.
Evidence has recently been found to support the idea of the environment influencing the genes within our lifetime. An Italian geneticist has located what might be the protein capable of transferring a foreign gene to all the genes in new cells, sperms and ovum and eventually into new offsprings.
This environmental connection to evolution is something not discussed by Charles Darwin in his theory of evolution.
18th century biologist Charles Darwin
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