Galactic controls

English: Artist's conception of the Milky Way ...
Artists impression of the Milky Way viewed along its axis. Image via Wikipedia

Palaeoclimatologists are quite content that an important element in controlling the vagaries of climate is due to gravitational forces that cyclically perturb Earth’s orbit, it axial tilt and the way the axis of rotation wobbles in a similar manner to that of a gyroscope. The predictions about this by James Croll in the late 19th century, which were quantified by Milutin Milankovich during his incarceration during World War I, triumphed when the predicted periods of change were found in deep-sea floor sediment records in 1972. Authors of ideas that link Earth system changes  to the progress of the Solar system through the Milky Way galaxy haven’t had the same accolades. One of the first to suggest a galactic link was Joe Steiner (Steiner, J. 1967. The sequence of geological events and the dynamics of the Milky Way Galaxy. Journal of the  Geological Society of  Australia, v.  14, p. 99–132.) but his work is rarely credited.

There has been an upsurge of interest in the last decade or so. In a recent issue of New Scientist Stephen Battersby reviews what galactic ‘forcings’ may have accomplished during the 4.5 billion-year history of our world (Battersby, S. 2011. Earth odyssey. New Scientist, v. 212 (3 December issue), p. 42-45). Having formed probably much closer to the galactic centre than its current position the Solar System has drifted, perhaps even ‘surfed’ gravitationally, outwards to reach its present ‘suburban’ position in one of the spiral arms. There are regularities to the now stabilised orbital movements: once every 200 million years the Solar System completes a full orbit; this orbit wobbles across the hypothetical plane of the galactic disc by as much as 200 light years, moving with and against the Milky Way’s cosmic motion. It has proved impossible so far to detect any sign of the orbital 200 Ma periodicity in events on the Earth, and most attention has centred on the wobble.

Steiner suggested that this motion may have crossed different polarities of the galactic magnetic field, perhaps triggering the periodicity of geomagnetic  changes in polarity, but this now seems unlikely. However, his suggestion that glacial epochs, such as those in the Palaeo- and Neoproterozoic, at the end of the Palaeozoic Era and at present, may have resulted from the Solar System’s passage through dust and gas banding in the Milky Way continues to have its attractions (e.g. Pavlov, A.A. et al. 2005. Passing through a giant molecular cloud: “Snowball” glaciations produced by interstellar dust, Geophysical Research Letters, v. 32, p. L03705). The direction of motion relative to the Milky Way’s cosmic drift governs the exposure to cosmic rays that result from a kind of ‘bow-shock’ ahead of the galaxy

Stellar motion through the Milky Way is semi-independent so that from time to time the Solar System may have been sufficiently close to regions of dense dust and gas that nurture the formation of super-massive stars. These huge objects quickly evolve to end in supernovae, proximity to which would have exposed life to ‘hard’ X- and  γ-rays and would be trigger for mass extinction, for instance by accompanying cosmic rays in destroying the ozone protection from UV radiation from the Sun.

The dynamism of the Earth and the resulting complexity of its surface processes makes it a poor place to look for physical signs of galactic influences. No so the Moon: for almost 4.5 billion years it has been a passive receptor for virtually anything that the cosmos could fling at it, and so geologically inert that its surface layers may well preserve a complete ‘stratigraphic’ record of all kinds of process. Should lunar landings with geological capabilities once more prove economically possible, or politically useful, that hidden history could be read.

3 thoughts on “Galactic controls

  1. Garry

    Shaviv’s work is a follow up of Joe Steiner’s original ideas, whether he acknowledges Steiner or not (the poor guy had a hard time in the 70’s when anything about extraterrestrial influences was widely regarded as Whizz-Bang science). I’m happy to learn about as many influences as there are, because climate is never going to a simple matter on the short- or long term – but I am no specialist. I knew Joe and if you are interested try chasing down some of his papers. e and I were at the University of Alberta when Jan Veiser was just starting his work on geochemical tracking of ancient climates. Sadly I never kept in touch with them after a few years, but remember both as men whose seminars always created a ruckkus!

    best wishes

    Steve Drury


    1. Steve,
      Thank you for touching so many subjects! I will read with interest more studies by Veiser. I have read an article where Shaviv was pretty complimentary of him and referenced numerous times.

      You are one prolific reader, writer and and educator! Nice to see someone that has your passion and skill. Have you done work on the geologic dynamics in the Pacific Northwest? Anything which really interests? I find the area incredible geologically. You seem to have had that same feeling with your research in India?

      This will be an exciting time for physcists studying the Earth if we get to experience a solar minimum.


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