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