Lunine (US), Jean-Marc Petit (IT), Francois Robert (FR), Giovanni B. Cyr (US) proposed that as the solar system formed, Jupiter's powerful gravity perturbed asteroids to accrete into larger and larger objects resulting in terrestrial "embyros" near the size of Mars. Towe (US), Edward Anders (US), Gustaf Olaf Arrhenius (SE-US), Bibhas Ranjan De (US), Hannes Olof Gosta Alfvén (SE-US), Anne Benlow (GB), Arthur Jack Meadows (GB), Manfred A. Ahrens (US) proposed that on the primitive Earth, impact accretions from extraterrestrial objects represented a significant source of atmospheric and biogenic elements (75, 113, 223, 233, 697, 1393, 1927, 2309, 2366). This "greenhouse" would have offset the effects of a faint young Sun which was dimmer than today’s by 25-30%. Grotzinger (US) used greenhouse calculations and the sedimentary record to suggest that prior to 3.8 Ga the Earth’s surface was a warm (80-100˚C), with a bicarbonate-rich ocean at a p H perhaps as low as 6 (1020, 1307, 1484). Francis Harry Compton Crick (GB), Sydney Brenner (ZA-GB), Aaron Klug (ZA-GB), and George Pieczenik (US) proposed that the assignment of codons to particular amino acids was simply an historical accident. Initially E was plentiful in the environment and was absorbed directly by primitive aggregates.
These "embryos were tossed into very unstable elliptical orbits with the result that some collided with Earth thereby delivering the water that now fills Earth's oceans. Climate models confirm that 100-1,000 times the present atmospheric level of carbon dioxide would have been necessary to produce the ancient "greenhouse" effect (1307). Allègre (FR), Thomas Staudacher (FR), and Philippe Sarda (FR) determined that early catastrophic out-gassing occurred on the young Earth (54, 2352). Walker (US) and Peter Brimblecombe (GB) found that abundant aqueous ferrous iron occurring in an oceanic hydrothermal system results in the precipitation of otherwise highly insoluble iron sulfides. There being no special reasons why a particular codon stands for a given amino acid (557). Later, as E became scarce because of use, chemical selection favored pre-cells that could make E from D, a slightly less complex organic substance still found in abundance in the environment. Mémoire sur les accidents des Coquilles fossiles, comparés à ceux qui arrivent aux Coquilles qu’on trouve maintenant dans la mer [Memory of accident fossil shells, compared to those who arrive in the shells now found in the sea].
Zh Zhang (CN) discovered large (40-200 micrometer) spherical microfossils 1.8 to 1.9 billion years old in sedimentary rocks from China.
These microfossils were interpreted to be the earliest know eukaryotes (Eucarya) (2674). All in the Day's Work: Leaves from a Doctor's Case-Book.
These events occurred when Earth was about half its present size (1655). Arvid Gustaf Högbom (SE) suggested that Earth's primitive atmosphere resulted from gradual, episodic, or rapid volcanic out-gassing and weathering (1179). This would have released significant amounts of nitrogen, carbon dioxide, carbon monoxide, methane, water, hydrogen, sulfur dioxide, and hydrogen sulfide. This suggests that on the primitive Earth such a system would have served as a highly effective sink for hydrogen sulfide (2553). Wood (GB) and David Virgo (US) presented evidence that Earth's primitive atmosphere was poised at a redox state buffered close to the fayalite-quartz-magnetite system, which is consistent with a neutral redox atmosphere and characteristic of basalts throughout the geological record (2649). As D became exhausted, selection favored assemblies that developed the pathway C to D to E, in which the even simpler substance C could be absorbed and used as raw material to make D. Memoires de l'Academie des Sciences, Paris: 189-226; 329-57; 99-419 1027.
Alexander Ivanovich Oparin (RU) postulated that a long chemical evolution in the oceans preceded the appearance of life on Earth (1741-1743). This process continued until the entire synthetic pathway, based on an essentially inexhaustible inorganic substance, was established (1207, 1208). Stetter (DE) concluded that the origin of life probably took place under conditions of high temperature because the hyperthermophiles are grouped around and occupy all of the deepest branches of the three kingdom phylogenetic scheme. Packer (US) found rock bearing 3.5 Ga microfossils within early Archean (Gk. The microfossils were interpreted to be prokaryotes and represent the oldest fossils known (2123). Banerjee (CA), Karlis Muehlenbachs (CA), Hubert Staudigel (US), and Maarten De Wit (NL) found tiny holes in volcanic glass. (US) indicated that the Archaea and Bacteria diverged from one another near the time that life arose on Earth. Observations qui peuvent servir à former quelques caractères de coquillages [Observations that can be used to train some shells character]. Guhl F, Jaramillo C, Yockteng R, Vallejo GA, Cardenas-Arroyo F.
Alveolates include dinoflagellates, apicomplexans, and ciliated protozoans. Transactions, Kentucky Medical Society 2: 265 1020.
The stramenopiles include brown algae, labyrinthulids, chrysophytes, xanthophytes, diatoms, and oomycetes (1806). William Schopf (US) discovered fossils of microorganisms in stromatolitic cherts of the Neoproterozoic Bitter Springs Formation of the Amadeus Basin of central Australia (162, 2119).
They represent the first fossil evidence for microbial life in a Precambrian submarine thermal spring system, and extend the known range of submarine hydrothermal biota by more than 2,700 million years. This was the first indisputable evidence of Precambrian life (2385). (US) later confirmed these findings and discussed their significance (163, 496). The position of the clade for this organism in the tree of life remains uncertain (874). Konstantin Sergejewitsch Mereschkowsky (RU) proposed the theory of the symbiotic origin of the eukaryotic cell and introduced the term symbiogenesis to signify the emergence of new species with identifiably new physiologies and structures as a consequence of stable integration of symbionts.
Such environments may have hosted the first living systems on Earth, consistent with proposals for a thermophilic origin of life. Roger Mason (GB) Tina Negus (GB) and other school children discovered in Charnwood Forest, England the Precambrian fossil remains of what may very well be the oldest known multicellular animal (later named Charnia). It stated that the chloroplast and mitochondria of eukaryotic cells had their origins from endosymbiotic cyanobacteria and aerobic bacteria, respectively, whose ancestors were once captured and incorporated by a primitive, anaerobic, heterotrophic host. An approach to the taxonomy of the Hominidae: Gracile Villafranchian hominids of Africa.
Charles Doolittle Walcott (US) described an important clue in the search for Precambrian life when he discovered fossils in Precambrian carbon-rich shales on the slopes of a prominent butte deep within the Grand Canyon.
The shales belonged to what is known as the Chuar Group of strata, so, Walcott named the fossils Chuaria.
Professor of Biology Delta State University Box 3262, Cleveland, MS 38733 e-mail: [email protected]“Reason was born, as it has since now discovered, into a world already wonderfully organized, in which it found its precursor in what is called life, its seat in an animal body of unusual plasticity, and its function in rendering that body’s volatile instincts and sensations harmonious with one another and with the outer world on which they depend.” George Santayana (2061) "The proper concern of natural science is not what God could do if he wished, but what he has done; that is, what happens in the world according to the inherent causes of nature." Albertus Magnus; Alberti Magni; Albert the Great (DE) (1004, 2020) Georges Eduard Lemaitre (BE) proposed that the universe began as a primal atom, an incredibly dense egg containing all the material for the universe within a sphere about 30 times larger than our Sun. E., was the first to teach that all heavenly bodies were brought into existence by the same processes that formed the earth and that all of these objects are made of the same materials (74).