Life on Earth even luckier than we thought?

Continually improving resolution of telescopes is now beginning to reveal signs of planetary systems around other stars.  Because their gravitational effects on stellar motion are detectable, the 60 or so known planets in distant stellar systems are all gas-giants, similar to but bigger than Jupiter.  Surprisingly, calculations show that such massive planets are in very different orbits than those in the Solar System.  Their orbits are highly eccentric, and bring them remarkably close to the star, unlike the almost circular orbits in the Solar System.   Yet, if they are mainly gaseous, they must have formed far from the warming influence of their companion star, as did Jupiter, Saturn, Uranus and Neptune.  Somehow, they have been gravitationally perturbed over the billions of years of evolution of the stellar systems.

How, then, did such bodies move inwards?  One possibility is that they exchanged angular momentum with smaller, rocky planets, forcing both into eccentricity.  For the smaller bodies the effect would be more dramatic, potentially either flinging them into interstellar space or into collision with their star.  Spanish and Swiss astronomers using spectroscopes at an observatory on the Canary Islands have discovered a large lithium anomaly in the spectrum of one star with such an aberrant gas giant (Israelian, G.  et al. 2001.  Evidence for planet engulfment by the star HD82943.  Nature, v. 411, p. 163-166).  Because the anomaly is accompanied by greater than usual abundances of many elements heavier than helium, and because lithium is quickly consumed as stars “ignite”, Israelian and colleagues conclude that the star has engulfed an Earth-like planet.

If such processes are common, and theory suggests that it may be, our Solar System could be one of very few in which potentially life-building and sustaining planets had sufficient time to develop a biosphere.  It seems that the more small planets there are between a star and an outer gas-giant, the more likely it is for such perturbations to take place.  The Solar System has only four, and calculations using Jupiter’s mass and orbit point to a minute tendency for such eccentricities to evolve.  Looking on the bright side, at least for those committed to a view of life pervading the cosmos, current observational resolution is only able to detect giant planets in wildly eccentric orbits.  Many planetary could be more stable.

Se also:  Samuel, E.  2001.  Banished forever.  New Scientist, 12 May 2001, p. 15.

Late-Palaeocene red tides?

About 55 Ma ago, in the late-Palaeocene, the carbon-isotope record shows a sudden drop in 13C, signifying a sudden release of methane from ocean-floor gas hydrates or clathrates.  That period also reveals evidence of s brief global warming, against the general trend of cooling through the  Tertiary.  Since the discovery of this massive discharge of the “clathrate gun”, palaeontologists have looked for ecological effects in sea-floor sediments.  For them to be significant, it is important that climate-related ecological effects occurred at the same time in widely separated parts of the globe.

Geologists from the Netherlands, Denmark, New Zealand, Austria and Sweden have examined the microfossil record from two late-Palaeocene sequences in Austria and New Zealand, and show such synchronicity (Crouch, E.M. et al.  2001.  Global dinoflagellate event associated with the late Palaeocene thermal maximum.  Geology, v. 29, p. 315-318).  Exactly at the time of the d13C dip in both sections, the abundance of cysts of single-celled phytoplankton known as dinoflagellates rose dramatically, only falling when carbon isotopes recovered to usual levels.  The authors link this to exceptionally high surface-water temperature and photosynthetic productivity.  Over the same period, the fossil record shows a mass extinction of benthonic organisms, and noticeable turnover and diversification of plankton and mammals, though not as dramatic as other biological events.

Today, dinoflagellates explode in numbers, along with other phytoplankton, under similar conditions and when nutrients increase in surface waters, to create phenomena known as “red tides”.  Because some species of dinoflagellates produce potent neurotoxins, “red tides” often result in massive death of marine animal life.  The effects linger as such toxins build up in the cells of animals, such as bivalves, which survive the bloom.  The air above such blooms is filled with stinging, choking aerosols, not far different from nerve gas.  Rotting of dead organisms causes oxygen levels in local seawater to drop, further adding to the death tool at deeper levels.  Red tides that result from human input of nutrients in sheltered embayments often sterilize them for long periods.

Although it is impossible to tell if such neurotoxins built up during the late-Palaeocene thermal maximum, that is not an impossibility.  Such biological “warfare” (no-one knows why some dinoflagellates produce the toxins) might explain the biological crisis that accompanied methane release.

A broader view of the Permian-Triassic mass extinction

That the Palaeozoic Era ended in the greatest mass extinction is well know, although why it happened is still a topic of fierce debate.  Part of the problem is that its effects on land and in the oceans emerge from studies of widely separated P-Tr sections, and many of these are extremely thin.  Such condensed sequences are notoriously difficult to resolve in terms of relative and absolute timing, as well as to correlate from place to place.

As with much else, Greenland promises to throw light on the end-Palaeozoic events, thanks to a 700 metre sequence of siliciclastic sediments in East Greenland that spans the Permian-Triassic boundary without a break.  Its most exciting feature is the way in which marine and non-marine sediments interleave with one another.  Geologists from the USA, the Netherlands, Australia and Britain have pieced together the evidence of biological change from a small part of this little described occurrence (Twitchett, R.J. et al.  2001.  Rapid and synchronous collapse of marine and terrestrial ecosystems during the end-Permian biotic crisis.  Geology, v.  29, p. 351-354).

In marine sediments, the Permian biota collapse, together with evidence for disturbance of the sediment structure by burrowing , in a mere 50 cm of the almost 40 metre sequence that the authors analysed.  Over the same interval, pollens of Permian land plants also fall dramatically, but all the pollen types linger through the overlying 15 metres.  Only at a level 25 metres above the biotic collapse do  fully Triassic faunas and floras appear.  From estimates of the rate of sedimentation the marine and terrestrial collapse appears to have taken between 10 and 30 ka.  Oddly, the now well-known fall in 13C does not coincide with that in the biota.  The authors visualize two possibilites: that it resulted from the collapse itself, or reflects an external factor that played little or no role.  One interesting scenario that they suggest is that it may indicate a major release of methane by breakdown of gas hydrates (a now increasingly popular mechanism!).

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