Biological Evolution in the Oceans
Author: Dr Simon HardingTheories of how life originated
There are several main theories of how life originated. Let us take these in rough chronological order. Firstly the theory of Panspermia. It was thought that micro-organisms had arrived on Earth from another part of the universe carried by meteorites or comets.
Secondly, since there was no real evidence for panspermia chemical theories of the origin of life arose and are more plausible at our current level of knowledge. Here the theory is that life arose from chemical reactions between organic molecules abiotically (not manufactured by organisms). Herman Muller felt that the first life forms must have been genes that replicated themselves and mutated allowing them to evolve. In 1923 Alexander Oparin hypothesized that over evolutionary time molecules within droplets of mixed oil/water became complex, with enzymes forming to organize other molecules into metabolic cycles. Genes would form later. JBS Haldane broadly agreed with this view.
These ideas modified when scientists realised that genetic code in the form of DNA had to come first and an energy source such as sunlight or lightening was also probably needed. In the 1950s Miller and Urey conducted experiments using flasks with chemicals as found in the early atmosphere, water and an electrical charge. Organic molecules were synthesized. This showed it was possible to synthesize organic molecules from ingredients found in the early history of the Earth. Later it became apparent that life may also have begun in the ocean depths fueled by hydrothermal vents. These are the main theories of how life originated.
Hydrothermal Vents.
Hydrothermal vent systems develop at depths of several kilometers in the oceans in mid ocean spreading centres where there is hot upwelling lava. Sea water percolates and is vented back at hot temperatures, full of minerals, as either warm seeps, black or white "smokers". There are many theories about how life may have originated around these vents and in fact these areas may even have been where photosynthesis first developed as there is a faint haze around these vents. The vent systems are highly dynamic and unstable environments but they do support over 200 species of life found so far. Three of the species that live in the vent systems are: 1) Riftia pachyptila or giant tube worms 2) Calyptogena magnifica or giant clams 3) Beggiatoa , a species of bacteria.
Radiations, extinctions and the Cambrian Era.
Radiations are relatively rapid increases in the diversity of organisms. Extinctions are the decreases in the diversity of organisms. The Cambrian explosion was the first major radiation that we can see from the limited fossil record. There have been five major mass extinctions that we can trace from the fossil record. These are in order the Late Ordovician, Late Devonian, Late Permian, Late Triassic and Late Cretaceous. All mass extinctions are associated with global climate changes and meteorite impacts may also have played their part.
It should be stressed that the fossil records are far from complete and much research remains in this area. The Cambrian era ending about 540 Ma contains the so called Cambrian explosion where life began to diversify at an extraordinary rate. In a relatively short period of geological time, over about 5 to 10 million years all the body plans of animals we know today evolved. We know this as we have evidence from the Burgess Shale fossil finds. This deposit was first discovered by Walcott and finds include animals such as Anomalocaris, Marella spledens and a range of trilobites. The Cambrian was also the era in which the first shelled animals appear in the sea so is very significant.
Characteristics of vertebrates.
Vertebrates consist of eight classes of animal and share many unique features such as Jointed backbone Hollow nerve cords developing into a brain and spinal cord Comparatively large size Specialization of parts. For example the formation of a head (cephalisation) which allows most of the sense organs to be located in an area that comes into contact with the environment first Bilateral symmetry Internal skeletons of bone/cartilage. Ribs helping to support and protect organs. Closed circulatory system Appendages which have been modified into limbs, fins and wings It is thought that vertebrates evolved as the size of animals increased generally and more support and better means of movement were needed.
Dr Simon Harding
www.chronosconsulting.com
Article Source: http://www.articlesbase.com/science-articles/biological-evolution-in-the-oceans-1622158.html
About the Author