Tides
The activity evidenced on Europa's surface is driven by tides. Tides generate periodic global stresses that crack and displace surface crust, as the thin shell of ice must accommodate to the changing global shape of the ocean below it. Moreover, tidal friction provides the dominant internal heat source, which keeps most of the thick water layer in the liquid state, as well as allowing occasional local or regional melting of the ice crust, either all the way through or just varying the ice...
The Ediacaran world
The terminal period of the Proterozoic, called Ediacaran after a locality in the Flinders Ranges of South Australia or Vendian in the Russian terminology , marks the first appearance of undoubted macrofossils. Because they are seemingly complex and because they have been studied mainly by palaeozoologists , all Ediacaran macrofossils were interpreted originally as early multicellular animals metazoans . The title of Martin Glaessner's 1984 monumental book, The Dawn of Animal Life, expresses...
The parasite connection
For most of us, endoparasites and pathogens have a negative connotation, and we think that the world would be better without them. In a less anthropocentric view, however, they appear to be essential for the long-term survival of all ecosystems. Like the arms race between predator and prey species at the trophic level, a constant race takes place between hosts and their parasites. But as we know, there is no ultimate winner, because most defence mechanisms and drugs work only at the level of...
References Esx
Bapteste, E., and Brochier, C. 2004 . On the conceptual difficulties in rooting the tree of life. Trends Microbiol., 12, 9-13. Bapteste, E., Boucher, Y., Leigh, J., and Doolittle, W.F. 2004 . Phylogenetic reconstruction and lateral gene transfer. Trends Microbiol., 12, 406-411. Beiko, R. J., Harlow, T. J., and Ragan, M.A. 2005 . Highways of gene sharing in prokaryotes. Proc. Natl. Acad. Sci. USA, 102, 14332-14337. Brown, J. R., and Doolittle, W. F. 1995 . Root of the universal tree of life...
Vendobionts as giant protozoans
As mentioned above, the view that the largest, most common and most diversified organisms of the Ediacaran biota were giant protozoans rather than metazoans was based mainly on their allometric compartmentation. Partly overturned fronds show that quilting patterns were identical on upper and lower surfaces. The penetration of two infaunal Pteridinium specimens by another individual and their growth responses to this accident Figure 10.1 are hard to reconcile with metazoans. So are the resting...
Hoststar metallicity
The chemical composition of a planet-hosting star is related to that of the primordial molecular cloud where the star formed. The metallicity is a measure of the relative amount of elements heavier than hydrogen and helium in the stellar atmosphere. Santos et al. 2004 have shown that the abundance of planets is strongly related to the metallicity of the host star. This effect is much stronger than the selection effect caused by the presence of more metal lines in the stellar spectrum e.g.,...
Environmental extremes Temperature
Why should temperature make a difference to organisms Organisms rely on biomolecules, all of which will break down at some temperature. For example, chlorophyll degrades near 75 C Rothschild and Mancinelli, 2001 . The melting temperature of nucleic acids depends on the base composition A-T bonds are less thermostable than are G-C bonds , the length of the polymer, and the solvent including the concentrations of ions in solution, but even DNA normally will degrade well below 100 C. Table 6.2....
What is an extremophile
The word 'extremophile', coined by Bob MacElroy 1974 from the Latin 'extremus' and the Greek 'philos', literally means 'lover of extremes'. Unfortunately, even the definition is not as clear as one might think. Extreme is usually taken to refer to physical, chemical, or, rarely, biological conditions. But what is extreme There is an objective definition of extreme, owing to the fact that life on Earth is based on organic carbon with water as a solvent. Thus, conditions that disrupt the...
Kimberella as a stemgroup mollusc
As stated previously, the presence of truly multicellular animals in the Late Proterozoic is documented by various kinds of fossils. While 'worm' burrows and ill-'VENDIAN SHALLOW-MARINE BIOMATSglllS ill-'VENDIAN SHALLOW-MARINE BIOMATSglllS Fig. 10.4. Because they survive in the present deep sea, xenophyophores are known to be giant rhizopods. Their chambers resemble vendobiontan quilts in size, shape, and allometric diameter, but walls are agglutinated and non-expandable. As a silty fill...
Phylogenetic implications
Hot volcanic environments are among the oldest biotopes existing on Earth. What is known about the phylogenetic relationships of the organisms living there Based on the pioneering work of Carl Woese, the small subunit ribosomal RNA ss-rRNA is widely used in phylogenetic studies of prokaryotes Woese and Fox, 1977 Woese et al., 1990 . It consists of approximately 1500 nucleotides and is homologous to its eukaryotic counterpart. On the basis of sequence comparisons, a phylogenetic tree is now...
Protein evolution
The previous section envisages early proteins composed of a small set of amino acids. Several studies have considered whether such proteins could be functional. Using only three amino acids Gln, Leu, and Arg , proteins with strong helical structure were found Davidson et al., 1995 . Doi et al. 2005 found that random sequences of the five most abundant early amino acids according to our ranking, Gly, Ala, Asp, Glu, and Val, were more soluble than random sequences of 20 amino acids or Gln-Leu-Arg...