THE FUTURE OF HELIOGEOLOGY

Heliogeology, hitherto mainly concerned with using terrestrial data to extend the Sun’s history up to 4.10⁹ yr beyond the four centuries of the sunspot record, can repay Earth science by clarifying the influence of solar radiation on the period and amplitude of key stratigraphic trends and oscillations throughout the solar system and its expanded exorealm. A recent example is the contribution of the Gurevich model of plasma expansion to the tripartite scheme of solar heating, as it appears to resolve the longstanding puzzle of coronal temperatures and their part in accelerating the solar wind and thus should help extract the climate signal from the cosmogenic ¹⁰Be record of ice cores. Similarly, by accounting for the diversity of speeds displayed by the solar wind, and thus opposing the customary fast/slow classification, it encourages distrust of the uncritical application of any periodicity - including the Schwabe ~11 yr interval - to components of geohistory.

The second main strand of the astronomical quid pro quo is a broadening of perspective by demonstrating that our earthly research area is arbitrarily poky. The identification of hundreds of exoplanets, some of them boasting paraterrestrial weathers and landscapes, increasingly requires divesting their exploration of the procedures and units that formerly seemed inescapable in stratigraphy and correlation. Our postulated plasma expansion into the near-vacuum of space underscores the commonalty of space weather and encourages the adoption of appropriate timescales subdivided independently of the phenomena being investigated. This principle would rule out a stratigraphy founded on physical or biological breaks, let alone such accusatory terms as anthropocene. The retention of the year or some variant of it such as light-year, rather than International Atomic Time (TAI), as the fundamental unit of geotime is also moot as it shelves scrutiny of an important variable component of our solar system. Long-distance time-correlation can already be done over spans measured in Astronomical Units (AU) using as markers the radioactive debris scattered by supernovae, such as that responsible for ⁶⁰Fe spikes in sediments laid down 2.2 and 1.5 Myr ago.