A 100,000-year periodicity in the accretion rate of interplanetary dust

A late Miocene dust shower from the break-up of an asteroid in the main belt

Throughout the history of the Solar System, Earth has been bombarded by interplanetary dust particles (IDPs), which are asteroid and comet fragments of diameter approximately 1-1,000 microm. The IDP flux is believed to be in quasi-steady state: particles created by episodic main belt collisions or cometary fragmentation replace those removed by comminution, dynamical ejection, and planetary or solar impact. Because IDPs are rich in 3He, seafloor sediment 3He concentrations provide a unique means of probing the major events that have affected the IDP flux and its source bodies over geological timescales. Here we report that collisional disruption of the >150-km-diameter asteroid that created the Veritas family 8.3 +/- 0.5 Myr ago also produced a transient increase in the flux of interplanetary dust-derived 3He. The increase began at 8.2 +/- 0.1 Myr ago, reached a maximum of approximately 4 times pre-event levels, and dissipated over approximately 1.5 Myr. The terrestrial IDP accretion rate was overwhelmingly dominated by Veritas family fragments during the late Miocene. No other event of this magnitude over the past approximately 10(8) yr has been deduced from main belt asteroid orbits. One remarkably similar event is present in the 3He record 35 Myr ago, but its origin by comet shower or asteroid collision remains uncertain.

Mid-Pleistocene revolution and the ‘eccentricity myth’

The mid-Pleistocene revolution (MPR) is the term used to describe the transition between 41 ka and 100 ka glacial-interglacial cycles which occurred about one million years ago. Despite eccentricity having by far the weakest influence on insolation received at the Earth’s surface of any of the orbital parameters, it is often assumed to be the primary driver of the post-MPR 100 ka climate cycles. The traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity. This ‘eccentricity myth’ is a simplified view of the relationship between global climate and orbital forcing and is in part due to an artefact of spectral analysis. Our aim here is to clarify the often confused role of eccentricity and review current theories of the MPR. We suggest that the post-MPR ‘100 ka’ glacial-interglacial cycles are more closely linked to precession, with the saw-toothed climate cycles being defined by every four or five precessional cycle. Because control over the number of precessional cycles involved is determined by eccentricity, eccentricity at most paces rather than drives the system. If true, then one must also question whether the MPR, itself defined by an abrupt change in spectral characteristics, is not also somewhat misconceived.

A short duration of the Cretaceous-Tertiary boundary event: evidence from extraterrestrial helium-3

Analyses of marine carbonates through the interval 63.9 to 65.4 million years ago indicate a near-constant flux of extraterrestrial helium-3, a tracer of the accretion rate of interplanetary dust to Earth. This observation indicates that the bolide associated with the Cretaceous-Tertiary (K-T) extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member of a comet shower. The use of helium-3 as a constant-flux proxy of sedimentation rate implies deposition of the K-T boundary clay in (10 +/- 2) x 10(3) years, precluding the possibility of a long hiatus at the boundary and requiring extremely rapid faunal turnover.