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At least 721 records · Page 40Linked to original sources
PubMed1987

The first 800 million years: environmental models for early Earth.

Space exploration has changed our views not only on the properties of celestial bodies and the interplanetary medium but also our perspective on the formation of such bodies, including the Earth. However, on few points do the new hetegonic insights approach certainty. More appropriately, they can be said to raise physically meaningful questions and to decrease the degrees of freedom allowable in any given scenario, which necessarily extends into the early history of the planetary crust, ocean and atmosphere. An attempt is made here to outline the basic schemes envisaged in modern studies of the origin of the Earth and the ramification of consequences for its early evolution that currently appear allowable and supported by observation.

Atmosphere↗
PubMed1991

Isotopic analysis of cometary organic matter.

Carbon isotope ratios have been measured for CN in the coma of comet Halley and for several CHON particles emitted by Halley. Of these, only the CHON-particle data may be reasonably related to organic matter in the cometary nucleus, but the true range of 13C/12C values in those particles is quite uncertain. The D/H ratio in H2O in the Halley coma resembles that in Titan/Uranus. The next decade should substantially improve our understanding of the distribution of C, H, N, and O isotopes in cometary organics. The isotopic composition of meteoritic organic matter is better understood and can serve as a useful analog for the cometary case.

Carbon↗
PubMed1996

Hippocampal participation in the sun compass orientation of phase-shifted homing pigeons.

The orientation of phase-shifted control and hippocampal lesioned homing pigeons with previous homing experience was examined to investigate the possible participation of the hippocampal formation in sun compass orientation. Hippocampal lesioned pigeons displayed appropriate shifts in orientation indicating that such birds possess a functional sun compass that is used for orientation. However, their shift in orientation was consistently larger than in control pigeons revealing a difference in orientation never observed in pigeons that have not undergone a phase shift. Although alternative interpretations exist, the data suggest the intriguing possibility that following a change in the light-dark cycle, the hippocampal formation participates in the re-entrainment of a circadian rhythm that regulates sun compass orientation.

Animals↗
PubMed1991

Astrometry of southern radio sources.

An overview is presented of a number of astrometry and astrophysics programs based on radio sources from the Parkes 2.7 GHz catalogues. The programs cover the optical identification and spectroscopy of flat-spectrum Parkes sources and the determination of their milliarc-second radio structures and positions. Work is also in progress to tie together the radio and Hipparcos positional reference frames. A parallel program of radio and optical astrometry of southern radio stars is also under way.

Astronomical Phenomena↗
PubMed1991

Upper limits for the ethyl-cyanide abundances in TMC-1 and L134N: chemical implications.

We have sought interstellar ethyl-cyanide via its 2(02)-1(01) transition towards two cold, dark clouds and report upper limits of the total column densities of 3 x 10(12) cm-2 and 2 x 10(12) cm-2 for TMC-1 and L134N, respectively. We also observed the 2(02)-1(01) transition of vinyl cyanide previously identified in TMC-1 by Matthews and Sears (1983b). The detection of vinyl cyanide and the non-detection of ethyl cyanide in TMC-1 are consistent with gas phase ion-molecule chemical models, and there is thus no necessity of invoking grain surface synthesis for vinyl cyanide in cold clouds.

Acrylonitrile↗
PubMed1995

Analysis of ras mutations in human melanocytic lesions: activation of the ras gene seems to be associated with the nodular type of human malignant melanoma.

We have analyzed the Ha-ras, Ki-ras and N-ras gene for point mutations at codons 12, 13 and 61 via restriction fragment length polymorphism/polymerase chain reaction analysis and subsequent direct sequencing in non-cultured fresh-frozen tissues of 16 superficial spreading melanomas (SSM), 13 nodular malignant melanomas (NMM), 2 lentigo malignant melanomas (LMM), 1 dysplastic nevus, 1 congenital nevus and 5 normal nevi from 38 patients. Mutations were found in 4 melanoma samples, all belonging to the nodular malignant type. Three of them were mutated in N-ras and one in the Ha-ras gene. Mutation in N-ras was also detected in the congenital nevus. All mutations were exclusively located at the first two base pairs of codon 61. No Ki-ras mutation was detected in any lesion. No mutation could be found in SSM and LMM in addition to dysplastic and normal nevi. The frequency of ras mutation in NMM was 31%, whereas in SSM it was 0%. Our study suggests (a) an association between ras mutations (mainly N-ras) and the NMM as a subgroup of human melanoma; (b) that activation of Ki-ras is not involved in the pathogenesis of melanoma. The role of UV radiation in point mutations of ras genes in human melanoma is discussed.

Base Sequence↗
PubMed1995

Solar activity cycle and the incidence of foetal chromosome abnormalities detected at prenatal diagnosis.

We studied 2001 foetuses during the period of minimal solar activity of solar cycle 21 and 2265 foetuses during the period of maximal solar activity of solar cycle 22, in all women aged 37 years and over who underwent free prenatal diagnosis in four hospitals in the greater Tel Aviv area. There were no significant differences in the total incidence of chromosomal abnormalities or of trisomy between the two periods (2.15% and 1.8% versus 2.34% and 2.12%, respectively). However, the trend of excessive incidence of chromosomal abnormalities in the period of maximal solar activity suggests that a prospective study in a large population would be required to rule out any possible effect of extreme solar activity.

Adult↗
PubMed1993

Intraocular pressure (IOP) in relation to four levels of daily geomagnetic and extreme yearly solar activity.

The link between geomagnetic field activity (GMA), solar activity and intraocular pressure (IOP) in healthy individuals was investigated. The IOP of 485 patients (970 eyes) was recorded over three nonconsecutive years (1979, 1986, 1989) which were characterized by maximal solar activity (1979, 1989) or minimal solar activity (1986). The measurements were also correlated with four categories of GMA activity: quiet (level I0), unsettled (II0), active (III0), and stormy (IV0). Participants were also differentiated by age and sex. We found that IOP was lowest on days of level IV0 (stromy) GMA. The drop in IOP concomitant with a decrease in GMA level was more significant during periods of low solar activity and in persons over 65 years of age. There was a trend towards higher IOP values on days of levels II0 and IV0 GMA in years of high solar activity. Differences between the sexes and among individuals younger than 65 years were not significant. Our results show an interesting aspect of environmental influence on the healthy population.

Adult↗
PubMed1996

Changes in human blood pressure with season, age and solar cycles: a 26 year record.

The record was studied of a 71-year-old, diurnally active (0700-2200 hours) male psychiatrist (G.N.) who self-measured systolic and diastolic blood pressure (BPS and BPD) mostly but not exclusively on Sunday mornings, from 1969 to 1994. A large about-yearly change was revealed which increased with age and was accompanied by a decreasing trend in the yearly rhythm-adjusted mean (MESOR; P < 0.01). According to conventional criteria that specify only upper limits of acceptability, G.N. was hypertensive in summer and normotensive in other seasons. Since changes in both MESOR and circannual amplitude occurred, a systematic surveillance of BP is the chronobiological recommendation.

Age Factors↗
PubMed1995

Relationship between immunoglobulin levels and extremes of solar activity.

The possible relationship between epidemics and extremes of solar activity has been discussed previously. The purpose of the present study was to verify whether differences in the levels of immunoglobulins (IgA, IgG, IgM) could be noted at the highest (July 1989) and lowest (September 1986) points of the last (21st) and present (22nd) 11-year solar cycle. The work was divided into a 1-month study (covering the month of minimal or maximal solar activity), a 3-month study (1 month before and after the month of minimal or maximal solar activity) and a 5-month study (2 months before and after the month of minimal or maximal solar activity). A trend of a drop-off for all three immunoglobulins was seen on the far side of the maximal point of the solar cycle. Statistical significance was achieved in the 5-month study for IgM (P = 0.04), and a strong trend was shown for IgG (P = 0.07). Differences between the sexes were also noted.

Female↗
PubMed1995

The effects of heavy meteorite bombardment on the early evolution--the emergence of the three domains of life.

A characteristic of many molecular phylogenies is that the three domains of life (Bacteria, Archaea, Eucarya) are clearly separated from each other. The analyses of ancient duplicated genes suggest that the last common ancestor of all presently known life forms already had been a sophisticated cellular prokaryote. These findings are in conflict with theories that have been proposed to explain the absence of deep branching lineages. In this paper we propose an alternative scenario, namely, a large meteorite impact that wiped out almost all life forms present on the early Earth. Following this nearly complete frustation of life on Earth, two surviving extreme thermophilic species gave rise to the now existing major groups of living organisms, the Bacteria and Archaea. [The latter also contributed the major portion to the nucleo-cytoplasmic component of the Eucarya]. An exact calibration of the molecular record with regard to time is not yet possible. The emergence of Eucarya in fossil and molecular records suggests that the proposed late impact should have occurred before 2100 million years before present (BP). If the 3500 million year old microfossils [Schopf, J. W. 1993: Science 260: 640-646] are interpreted as representatives of present day existing groups of bacteria (i.e., as cyanobacteria), then the impact is dated to around 3700 million years BP. The analysis of molecular sequences suggests that the separation between the Eucarya and the two prokaryotic domains is less deep then the separation between Bacteria and Archaea. The fundamental cell biological differences between Archaea and Eucarya were obtained over a comparatively short evolutionary distance (as measured in number of substitution events in biological macromolecules). Our interpretation of the molecular record suggests that life emerged early in Earth's history even before the time of the heavy bombardment was over. Early life forms already had colonized extreme habitats which allowed at least two prokaryotic species to survive a late nearly ocean boiling impact. The distribution of ecotypes on the rooted universal tree of life should not be interpreted as evidence that life originated in extremely hot environments.

Amino Acid Sequence↗
PubMed1992

Bolide impacts and the oxidation state of carbon in the Earth's early atmosphere.

A one-dimensional photochemical model was used to examine the effect of bolide impacts on the oxidation state of Earth's primitive atmosphere. The impact rate should have been high prior to 3.8 Ga before present, based on evidence derived from the Moon. Impacts of comets or carbonaceous asteroids should have enhanced the atmospheric CO/CO2 ratio by bringing in CO ice and/or organic carbon that can be oxidized to CO in the impact plume. Ordinary chondritic impactors would contain elemental iron that could have reacted with ambient CO2 to give CO. Nitric oxide (NO) should also have been produced by reaction between ambient CO2 and N2 in the hot impact plumes. High NO concentrations increase the atmospheric CO/CO2 ratio by increasing the rainout rate of oxidized gases. According to the model, atmospheric CO/CO2 ratios of unity or greater are possible during the first several hundred million years of Earth's history, provided that dissolved CO was not rapidly oxidized to bicarbonate in the ocean. Specifically, high atmospheric CO/CO2 ratios are possible if either: (1) the climate was cool (like today's climate), so that hydration of dissolved CO to formate was slow, or (2) the formate formed from CO was efficiently converted into volatile, reduced carbon compounds, such as methane. A high atmospheric CO/CO2 ratio may have helped to facilitate prebiotic synthesis by enhancing the production rates of hydrogen cyanide and formaldehyde. Formaldehyde may have been produced even more efficiently by photochemical reduction of bicarbonate and formate in Fe(++)-rich surface waters.

Atmosphere↗
PubMed1992

Comets and the formation of biochemical compounds on the primitive Earth--a review.

Thirty years ago it was suggested that comets impacting on the primitive Earth may have represented a significant source of terrestrial volatiles, including some important precursors for prebiotic synthesis (Oró, 1961, Nature 190: 389). This possibility is strongly supported not only by models of the collisional history of the early Earth, but also by astronomical evidence that suggests that frequent collisions of comet-like bodies from the circumstellar disk around the star beta Pictoris are taking place. Although a significant fraction of the complex organic compounds that appear to be present in cometary nuclei were probably destroyed during impact, it is argued that cometary collisions with the primitive Earth represented an important source of both free-energy and volatiles, and may have created transient, gaseous environments in which prebiotic synthesis may have taken place.

Atmosphere↗
PubMed1984

Chemical evolution and the origin of life: bibliography supplement 1982.

The bibliography is the thirteenth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci. 2(1970), 225-295; 3(1972), 293-304; 4(1973), 309-329 and in Origins of Life 5(1974), 505-527; 6(1975), 285-300; 7(1976); 75-85; 8(1977), 59-66; 9(1978), 67-74; 10(1980), 69-87; 10(1980), 379-404; 11(1981), 273-288; 12(1982), 93-118; 13(1983), 61-80.

Earth, Planet↗
PubMed1991

Electrical energy sources for organic synthesis on the early Earth.

In 1959, Miller and Urey (Science 130, 245) published their classic compilation of energy sources for indigenous prebiotic organic synthesis on the early Earth. Much contemporary origins of life research continues to employ their original estimates for terrestrial energy dissipation by lightning and coronal discharges, 2 x 10(19) J yr-1 and 6 x 10(19) J yr-1, respectively. However, more recent work in terrestrial lightning and point discharge research suggests that these values are overestimates by factors of about 20 and 120, respectively. Calculated concentrations of amino acids (or other prebiotic organic products) in the early terrestrial oceans due to electrical discharge sources may therefore have been equally overestimated. A review of efficiencies for those experiments that provide good analogues to naturally-occurring lightning and coronal discharges suggests that lightning energy yields for organic synthesis (nmole J-1) are about one order of magnitude higher than those for coronal discharge. Therefore organic production by lightning may be expected to have dominated that due to coronae on early Earth. Limited data available for production of nitric oxide in clouds suggests that coronal emission within clouds, a source of energy heretofore too uncertain to be included in the total coronal energy inventory, is insufficient to change this conclusion. Our recommended values for lightning and coronal discharge dissipation rates on the early Earth are, respectively, 1 x 10(18) J yr-1 and 5 x 10(17) J yr-1.

Earth, Planet↗
PubMed1991

A note on the prebiotic synthesis of organic acids in carbonaceous meteorites.

Strong similarities between monocarboxylic and hydroxycarboxylic acids in the Murchison meteorite suggest corresponding similarities in their origins. However, various lines of evidence apparently implicate quite different precursor compounds in the synthesis of the different acids. These seeming inconsistencies can be resolved by postulating that the apparent precursors also share a related origin. Pervasive D enrichment indicates that this origin was in a presolar molecular cloud. The organic acids themselves were probably synthesized [correction of synthesised] in an aqueous environment on an asteroidal parent body, the hydroxy (and amino) acids by means of the Strecker cyanohydrin reaction.

Amino Acids↗
PubMed1992

Comet Halley as an aggregate of interstellar dust and further evidence for the photochemical formation of organics in the interstellar medium.

Photolysis of mixtures of CO:NH3:H2O at 12 K results in the formation of an organic residue which is not volatile in high vacuum at room temperature. Analysis of this fraction by GC-MS resulted in the detection of C2-C3 hydroxy acids and hydroxy amides, glycerol, urea, glycine, hexamethylene tetramine, formamidine and ethanolamine. Use of isotopically labeled gases made it possible to establish that the observed products were not contaminants. The reaction pathways for the formation of these products were determined from the position of the isotopic labels in the mass spectral fragments. The significance of these findings to the composition of comets and the origins of life is discussed.

Dust↗
PubMed2006

p53 codon 72 polymorphism in basal cell carcinoma of the skin.

Basal cell carcinoma (BCC) is the most prevalent cancer in Iran. A common polymorphism at codon 72 of exon 4 of p53 tumor suppressor gene has been reported to be associated with increased inheritable susceptibility to several cancers. In the present study the frequency of p53 codon 72 polymorphism in 91 patients with BCC of skin, compared to 465 healthy normal individuals, was investigated. In total, there was no significant difference in the p53 genotypes between patients and controls. However, there was an apparent increase in the Arg/Arg genotype among those BCC patients who had a history of occupational sun exposure, compared to non-exposed patients (46.3% vs. 23.1%, P=0.11). A trend of increase in the frequency of Arg allele among sun-exposed patients was also observed (69.4% vs. 53.8%, P=0.07). Comparison of the genotype frequencies between sunexposed patients and normal controls confirmed the accumulation of Arg/Arg genotype in these patients (46.3% vs. 34.8%, P = 0.07). In addition, the frequency of Arg allele was significantly higher in sunexposed patients compared to controls (69.4% vs. 58.2%, P=0.03). Our results suggest that Arg allele at codon 72 of p53 gene might affect the risk of ultraviolet-induced basal cell carcinoma.

Codon↗