Engineering topics

Mills, T.

Publications and source records attributed to Mills, T..

6 records

NASA NTRS1995

Comets and life in the Universe

The notion that comets supplied the primitive Earth with the requisite chemical species for the process of chemical evolution, which is widely held to have led to the origin of life on Earth, has now gained considerable intellectual momentum since its first formulation in 1961. The role of comets in the Earth's biogenesis has been thoroughly addressed in the literature. At this time, in light of a few recent findings, we present here a concise review of this topic together with a brief discussion of the possible role of cometary material in the origin of life elsewhere in the Universe.

Oro, J.↗

NASA NTRS1995

On the levels of enzymatic substrate specificity: Implications for the early evolution of metabolic pathways

The most frequently invoked explanation for the origin of metabolic pathways is the retrograde evolution hypothesis. In contrast, according to the so-called 'patchwork' theory, metabolism evolved by the recruitment of relatively inefficient small enzymes of broad specificity that could react with a wide range of chemically related substrates. In this paper it is argued that both sequence comparisons and experimental results on enzyme substrate specificity support the patchwork assembly theory. The available evidence supports previous suggestions that gene duplication events followed by a gradual neoDarwinian accumulation of mutations and other minute genetic changes lead to the narrowing and modification of enzyme function in at least some primordial metabolic pathways.

Lazcano, A.↗

NASA NTRS1992

The cometary contribution to prebiotic chemistry

The chemical composition of cometary nuclei is examined to estimate the potential contribution of volatiles to the prebiotic earth from cometary collisions. Observations of cometary nuclei are reviewed to describe the chemical evolution of the objects and their theoretical potential for affecting the terrestrial environment. Specific attention is given to the plausibility of the single-impact formation of the earth-moon system, and experiments are proposed for testing the present theories. It is proposed that significant contributions of biogenic elements such as C, H, N, O, P, and S resulted from these nuclei colliding with the earth. Observations of the solar atmosphere and of the circumstellar shells of C-rich stars indicate that compounds such as CO, C2, and H2O were not pyrolyzed as a result of collision events. The compounds are theorized to have established the foundation for the abiotic synthesis of key biochemical molecules.

Oro, J.↗

NASA NTRS1992

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 (Oro, 1961). 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 cometlike 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.

Oro, J.↗

NASA NTRS1990

Prebiotic synthesis of histidyl-histidine

Histidyl-histidine (His-His) has been synthesized in a yield of up to 14.4% under plausible prebiotic conditions using histidine (His), cyanamide, and 4-amino-5-imidazole carboxamide. A trace amount of His trimer was also detected. Because the imidazole group of His is involved in a number of important enzymatic reactions, and His-His has been shown to catalyze the prebiotic synthesis of glycyl-glycine, we expect this work will stimulate further studies on the catalytic activities of simple His-containing peptides in prebiotic reactions.

NASA Discipline Exobiology↗

NASA NTRS1989

Chemical evolution of primitive solar system bodies

Observations on organic molecules and compounds containing biogenic elements in the interstellar medium and in the primitive bodies of the solar system are reviewed. The discovery of phosphorus molecular species in dense interstellar clouds, the existence of organic ions in the dust and gas phase of the comas of Comet Halley, and the presence of presolar, deuterium-hydrogen ratios in the amino acids of carbonaceous chondrites are discussed. The relationships between comets, dark asteroids, and carbonaceous chondrites are examined. Also, consideration is given to the chemical evolution of Titan, the primitive earth, and early Mars.

Oro, J.↗