Claudio Vita-Finzi

Coastlines, Submerged Landscapes, and Human Evolution: The Red Sea Basin and the Farasan Islands

ABSTRACT We examine some long-standing assumptions about the early use of coastlines and marine resources and their contribution to the pattern of early human dispersal, and focus on the southern Red Sea Basin and the proposed southern corridor of movement between Africa and Arabia across the Bab al-Mandab Straits. We reconstruct relative sea levels in light of isostatic and tectonic effects, and evaluate their paleogeographical impact on the distribution of resources and human movement. We conclude that the crossing of the Bab al-Mandab posed little significant or long-lasting physical or climatic barrier to human transit during the Pleistocene and that the emerged continental shelf during periods of low sea level enhanced the possibilities for human settlement and dispersal around the coastlines of the Arabian Peninsula. We emphasize the paleogeographical and paleoenvironmental significance of Pleistocene sea-level change and its relationship with changes in paleoclimate, and identify the exploration of the submerged continental shelf as a high priority for future research. We conclude with a brief description of our strategy for underwater work in the Farasan Islands and our preliminary results.

Neotectonics of the Vajont dam site

Abstract The disastrous Vajont landslide (NE Italy) of 9 October 1963 is generally thought to have occurred on an existing failure surface. Reassessment of the morphological and structural evidence suggests that movement was on a normal fault plane which had juxtaposed Cretaceous limestone and highly fractured rock debris, thus rendering the dam site unusually susceptible to massive sliding. The proposed fault is consistent in strike with the regional lineament pattern. Although movement was triggered by the combined effects of heavy rainfall and changes in reservoir level, there is circumstantial evidence that seismicity played a contributory part in mobilising the slide by increasing pore pressure at the base of the slide as well as by any associated shaking.

Loess and dust on Earth and Mars: particle generation by impact mechanisms

Impact between windblown quartz grains as a source of desert dust is consistent with laboratory abrasion experiments and has received some field confirmation in the Negev. The suggestion is that an important process on Mars now gains support from laboratory studies; even though their geochemical interpretation is controversial, they show that dust generation by impact is tenable even for quartz.A simple mechanism for small dust production from sand seas is proposed; internal stresses can be mobilized by impact energy. A speculative mechanism (the andesite scenario) is proposed for fine particle production by particle impact on Mars. The internal stress range in terrestrial sand grains may vary, depending on the nature of the source rock, and this may influence particle production by impact processes.

Looking at the Sun

Determining t1 and t2, we have a part whose retardance is specified at a center wavelength, and whose retardance is stable over temperature changes (see figure 4). Note that it is not strictly possible to design the part to be achromatic and athermal. Two thicknesses—that is, two degrees of freedom—can not accommodate the three constraints of retardance, retardance slope, and temperature insensitivity; however, a little give and take with the specifications can lead to acceptable performance in all three.

A size control for quartz silt (making particulates at planetary surfaces)

Quartz silt is widespread in terrestrial sediments [1]. Its ubiquity has led to its neglect as a geomaterial, and studies of silt as such are relatively rare, but it presents an interesting and continuing petrological problem. Is silt a specific geological material, is it defined by a formation process, and a set of size parameters? In the world of clastic quartz sedimentology there are obvious mode sizes; there is a sand mode at around 300–500 μm and a silt mode, an order of magnitude smaller, at 30–50 μm. Are these both defined by specific geological processes?

The Solar Nucleus

The Sun, which embodies much of the mass of our solar system, has evolved substantially since its coagulation from the nebula. It is at the heart of the solar system in many ways besides its obvious gravitational role, notably through the radiation it emits at a range of wavelengths, the magnetic heliosphere and the solar wind. All fluctuate periodically, irregularly and cumulatively in response to factors working within the Sun or externally, notably orbital cycles, interaction between bodies, and interstellar matter.

The Evolving Solar System

Advances in the observation of the heavens from the ground and from satellites, novel computational techniques, and theoretical advances in a number of related (and some unrelated) fields permit changes in the solar system to be monitored in ever increasing detail. The greatest progress has been in analysing the dynamics of the Earth, the Sun’s EUV radiation, and the inflow of comets and asteroids. The outcomes bear on the physical and chemical processes that modify the solar system.

The Solar Cycle

The ~11-year solar cycle was first identified in the fluctuation of the number and location of sunspots and, soon after, their magnetic polarity and the dipole component of the Sun’s magnetism as a whole. The cycle is manifested in satellite records of total and variable solar luminosity, in the open solar magnetic flux, which can be estimated from solar observation or from the aa geomagnetic index, and in the Sun’s radio emission The incidence of flares and coronal mass ejections is linked to the cycle in complex fashion. The Babcock model of sunspot generation relates the cycle to twisting of magnetic field lines by differential solar rotation; deeper links to internal dynamics are revealed by neutrino data. Periodicities which were not obvious when solar observation was limited to the photosphere may turn out to be more significant as regards the solar interior than the Schwabe or Hale cycle.

Lessons from History

The long-term history of the Sun is patchy, being based mainly on the implications of the Standard Solar Model and the record of flares recovered from the lunar regolith and meteorites exposed to cosmic rays at different times. However the fossil neutrino evidence, especially from tellurides, may eventually provide successive snapshots of the solar interior. Cyclical and aperiodic changes in TSI and UV are well documented for recent millennia, although they may turn out to be minor oscillations with wavelengths measured in ≥104 yr, and they provide the basis for approximate but robust forecasts for solar behaviour and its impact on space weather and terrestrial climate.

The Young Sun

Meteorites and the Moon yield information on solar flares and the solar wind which, though patchy, spans 109 yr. However, as the solar wind and flares are primarily creatures of the corona they are poor measures of solar activity as a whole. According to the Standard Solar Model the Sun’s luminosity has increased from 0.7 to 1.0 L☉ in the course of the last 4.5 Gyr. The widespread presence of liquid water on the Earth’s surface at least during the last 3.8 Gyr conflicts with this finding. Various mechanisms have accordingly been proposed for warming the early Earth, including atmospheric greenhouse effects, variations in cloud cover, and the prevalence of oceans with a low albedo. Changes in the mass of the early Sun and in its activity have also been suggested in order to reconcile the SSM with the geological evidence on Earth.