Microscopic fossils

However, the question of when exactly the first life forms emerged is by no means settled the date set by Schopf, 3.465x 109 years, is now in doubt. Schopf has recently introduced a new, ultramodern analytical method, laser Raman spectroscopy, as a highly sensitive technique for the study of microscopic fossil material. With the help of this method, it is possible to determine the chemical composition and also the two-dimensional structure of fossils (Kudryavtsev et al., 2001). 

Long recognized to be a critical problem in the hunt for early records of life (Tvler and Barghoorn, 1963), questions regarding the biogenicity of putative Precambrian microscopic fossils— particularly those of especially great geologic age— persist to the present (Brasier... 

Kudryavtsev A. B., Schope J. W., Agresti D. G. and Wdowiak T. J. (2001) In situ laser-Raman imagery of Precambrian microscopic fossils. Proc. Natl Acad. Sci. USA 98, 823 -826. 

In the rarefied intellectual atmosphere of London, Hooke began his independent career of many astouhdingly diversified achievements. He enunciated the relationship known as Hooke s law, which states that stretching in an elastic body, such as a spring, is proportional to the force applied. This law was later used to describe the motion of atomic nuclei in molecules. Hooke used a telescope to make several original astronomical observations and a microscope to describe snowflakes, cells (a word he first used), and microscopic fossils. Hooke speculated on using the barometer to predict weather, but he later doubted its efficacy, confounded no doubt by variables that weather forecasters still struggle with today. 

The early period of the Earth s history, around 3.8 1 billion years ago, is completely shrouded in darkness possible witnesses from this archaic period might help to cast some light. So we are looking for possible remains of the first primitive life forms on our planet—fossils, or to be exact, microfossils, which refers to the remains of living cells. What have survived are mainly only cell walls, which can be isolated from sedimentary rocks when the silicate-, sulphide- or carbonate-rich minerals are chemically dissolved away. The microfossils are found in the remaining carbon-containing residue, transparently thin platelets of which are prepared for microscopic studies. 

Cellular fossils can be studied under the microscope, and more recently, laser Raman spectroscopy has been used (see below). The platelets often show cells with sizes, shapes, cell structure and colony shapes similar to those of today s microorganisms. These properties could not have survived if the rocks had been heated to temperatures above 420 K, and the fossils also would not have withstood high pressures. 

William Schopf studied supercrustal rock samples from Akilia Raman and ion microscopic photographs showed the presence of carbon-containing inclusions in grains of apatite. The carbon isotope ratio was determined by secondary ion mass spectroscopy (SIMS) the 813C value was -29% 4%, in agreement with earlier analyses. This in turn confirmed the values obtained by Mojzsis (1996), which had been questioned by Lepland et al. three years later. The final verdict on the oldest fossils in western Greenland may not be reached for several years yet (McKeegan et al., 2007 Eiler, 2007). 

Successfully applying the method used by Fenton to prepare his concentrates depends upon two factors. First, there must be adequate density differences between the macerals in the sample, and second, there must be an initially high concentration of the required maceral. In attempting to separate either resinite or cutinite from sporinite of the same coal, neither of these conditions can be fulfilled, at least when the coal is of bituminous rank or higher. If, however, samples on a semi microscale are acceptable, it is possible to prepare concentrates of resinites of satisfactory purity from bituminous coals by simple mechanical means. The method has been described by Murchison and Jones (17) and mainly involves picking with fine probes on differently prepared surfaces of coal under a stereoscopic microscope. Resinites from lignites pose less of a problem because their occurrence in fairly substantial lumps is quite common these and fossil resins such as kauri gum and amber usually can be prepared to a purity of almost 100% with ease. 

QUALITATIVE COMMENTS (with 160 mg followed at 2 h by 60 pgs LSD) The visual phenomena were extraordinary. Wc were at the beach just south of Mendocino. In anything that had ever been living, there was an endlessly deep microcosm of detail. Endless, and forever more microscopic in intricacy. A sea urchin shell, a bit of driftwood, a scrap of dried seaweed, each was a treasure of jewels. I have never had such wealth of visual eroticism and bliss before. Later, we visited the pygmy forest, but these living fossils were not as magical. 

In a probe for the presence of stereoelectronic effects in nucleophilic addition to 12 sterically unbiased ketones, calculations have identified subtle bond length differences in the C-Nu bond of the diastereomeric alcohol products, where Nu- = H-or Me-.304 The calculated differences are weak (<1%) but consistent the bond is longer in the major product, acting as a fossil record of the TS. Using microscopic reversibility, the easier bond to cleave (the longer one) is the easier to form. The effect bears comparison with the kinetic anomeric effect in sugars, where such bond length differences in calculation are borne out in X-ray crystal structures. 

In order to overcome these problems, interest was focussed on that portion of the organic matter trapped in mineral precipitates which formed synchronously with sedimentation. In these cases, the material is hermetically sealed in the crystalline matter and may survive with relatively little subsequent alteration. Such preservation is common in cherts which are chemical precipitates of silica and now comist of fine grained quartz. These rocks offer the best chance for successful preservation of truely Precambrian molecular fossils. Modem microprobes and spectrophotometer microscopes allow the non-destructive analysis of organic matter enclosed in mineral crystals. Laser bombardment of microscopic... 

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