Cambrian period

Finally, if we take a fruit fly and knock out one of its Hox genes and then replace it with the corresponding human Hox gene, we get a perfectly normal fruit fly. As Matt Ridley has phrased it Flies and people are just variations on a theme of how to build a body that was laid down in some worm-like creature in the Cambrian period. This is a remarkable example of the underlying unity of living organisms. 

Fig. 7.1. The old model is driven by the idea of descent with variation, meaning that all organisms start from one event, followed by speciation about every 10,000,000 years. For those of us who do not tmst mathematics, this scheme shows that the process would produce 32 species from the beginning of the Cambrian to the end of that period, assuming that no extinction had occurred. This observation has to square with a reality that produces 120 genera of 30 major forms in the immediate post-Tommotian segment of the Cambrian Period.

Fig. 13.5. This figure is a summary of the various postulates of the genomic potential hypothesis. Coding sequences evolve from straight chemistry in innumerable pools on the earth s surface to provide a nearly unlimited reservoir of nucleic acid polymers which form themes and variations that are taken up by the various foci of cell formation. Once a cell has formed, it never loses its basic character, remaining either a micro-organism or developing a potential for a large animal during this 3.5 million years of the Archean period which would show up at varying times after the Cambrian period. Each new species eventually appears from its own pro- form and persists until the present or extinction.

Evolution of genotypes occurred during the pre-Cambrian period. Not much happened until about 600 million years ago. 

Trainor described algae as photosynthetic, nonvascular plants that contain chlorophyll a and have simple reproductive structures. 29 The fossil record indicates that algae may have existed before the Cambrian period.30 This survey focuses on marine macroalgae, commonly referred to as seaweed. Seaweeds are the largest forms of algae and live attached to solid substrata between and... 

Ordovician Period Geologic period of the Paleozoic Era after the Cambrian Period between 500 and 435 million years ago. Major advances during this period include the bony fish and possibly land plants (during the late Ordovician). 

This is the approximate age of the rock. It was formed sometime during the Cambrian Period. 

As stated above, carbonate rocks comprise —30% of the mass of Phanerozoic sediments. Given and Wilkinson (1987) reevaluated aU the existing data on Phanerozoic carbonate rocks, their masses, and their relative calcite and dolomite contents (Figure 38). It can be seen that, as with the total sedimentary mass (Garrels and Mackenzie, 1971a,b), the mass of carbonate rock preserved is pushed toward the front of geologic time. The Tertiary, Carboniferous, and Cambrian periods are times of significant carbonate preservation, whereas the preservation of Silurian and Triassic carbonates is minimal. 

Fossil shells recognizable as gastropods and bivalves are present in rocks from the Cambrian period, about 570 million years ago. Present classifications based on the evolutionary relationships of mollusks are derived from studies of embryonic development, comparative anatomy, and RNA nucleotide sequences. The findings suggest affinities of mollusks with sipunculid, annelid, and echiurid worms. 

An invertebrate is essentially a multicellular animal that lacks a spinal column encased in vertebrae and a distinct skull. There are about 30 phyla, or groups, of invertebrates, and roughly 20 of these have been preserved as fossils. Still other phyla probably existed, but are not represented in the fossil record because the animals soft bodies were not preserved. Only one invertebrate phylum is known to have become extinct— the Archaeocy-athida. These organisms, which were superficially similar to sponges, did not survive past the Middle Cambrian period (530 million years ago). 

Now, what is the situation of much older strata than the Cambrian period The iron ore strata in the Canadian Shield are known to have been formed 2750 million years ago. The isotopic ratio of the sulfide ores in the strata is 22.49, and this ratio suggests that the number of the bacteria which resided in the strata was one tenth of that of the bacteria in the present day. The strata in the Isua area in West Greenland are known to have been formed 3700 million years ago. The isotopic ratio of the sulfide ores in the strata is 22.24. The researchers have concluded that this ratio suggests that the bacteria have not resided in the strata. Therefore, the age of the... 

In the Cambrian period life began to develop very quickly. For this reason the oxygen concentration increased rather rapidly. Thus, in the late Silurian (420 millions years ago) the oxygen level was as high as 0.1 PAL (Fig. 3) which is termed the second critical level. With the increase of the oxygen concentration the quantity of ozone in the atmosphere increased, together with an increase in the altitude of maximum ozone production. This latter, in the late Silurian period reached 20 km level, which made the spread of life onto dry land possible. At the same time the thermal structure of the atmosphere was drastically changed, which resulted in the appearance of the stratosphere. It was shown previously that our atmosphere has an... 

Cambrian explosion sudden proliferation of many different types of complex animals around the beginning of the Cambrian period (543 million years ago). 

Precambrian geological period accounting for nine tenths of Earth s history, from its formation about 4.6 billion years ago until the Cambrian period S43 million years ago. prokaryote cell without nucleus, such as a bacterium. 

Alkanes in Fossil Fuels. Sedimentary rocks, which range in age from Recent years) to the pre-Cambrian period ( 3 x 10 ... 

Cambrian explosion A relatively short interval of rapid intense evolution that supposedly occurred in the early to mid-Cambrian period, some 540 to 520 million years ago. The supposition is based on the sudden appearance in the fossil record from this time of many diverse and novel forms, particularly marine animals, among which can be found representatives of all major modern groups. See Burgess shale. 

Phanerozoic The most recent eon of geological time, represented by rock strata containing clearly recognizable fossils. It comprises the Palaeozoic, Mesozoic, and Cenozoic eras and has extended for about 542 million years from the beginning of the Cambrian period. Compare Proterozoic. 

All investigators agree that the rocks of the Byrd Group were deposited during the Cambrian Period because the Shackleton Limestone as well as the Taylor Formation (in the Shackleton Glacier area) contain fossils of Cambrian age (Laird and Waterhouse 1962 Hill 1964a, b Palmer and Gatehouse 1972 Yochelson and Stump 1977 Debrenne and Kruse 1986). 

The Sr concentration of the Shackleton Limestone adjacent to the pegmatite is 179.3 ppm and its Sr/ Sr ratio is 0.70996 0.00031. The comparatively high value of the Sr/ Sr ratio of the Shackleton Limestone is consistent with the increase in this ratio in the oceans during the Cambrian Period which peaked during the late Middle Cambrain at about 0.7093 (Faure and Mensing 2005). 

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