The rate of supernovae (SNe) in our local galactic neighborhood within a distance of ~100 parsec from Earth (1 parsec (pc)=3.26 light years) is estimated at 1 SN every 2-4 million years (Myr), based on the total SN-rate in the Milky Way (2.0±0.7 per century1,2). Recent massive-star and SN activity in Earth’s vicinity may be evidenced by traces of radionuclides with half-lives t1/2 ≤100 Myr3-6, if trapped in interstellar dust grains that penetrate the Solar System (SS). One such radionuclide is 60Fe (t1/2=2.6 Myr)7,8 which is ejected in supernova explosions and winds from massive stars1,2,9. Here we report that the 60Fe signal observed previously in deep-sea crusts10,11, is global, extended in time and of interstellar origin from multiple events. Deep-sea archives from all major oceans were analyzed for 60Fe deposition via accretion of interstellar dust particles. Our results, based on 60Fe atom-counting at state-of-the-art sensitivity8, reveal 60Fe interstellar influxes onto Earth 1.7–3.2 Myr and 6.5–8.7 Myr ago. The measured signal implies that a few percent of fresh 60Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ~10 Myr at nearby distances ≤100 pc.

Half of the heavy elements including all actinides are produced in r-process nucleosynthesis, whose sites and history remain a mystery. If continuously produced, the Interstellar Medium is expected to build-up a quasi-steady state of abundances of short-lived nuclides (with half-lives ≤100 My), including actinides produced in r-process nucleosynthesis. Their existence in today’s interstellar medium would serve as a radioactive clock and would establish that their production was recent. In particular 244Pu, a radioactive actinide nuclide (half-life=81 My), can place strong constraints on recent r-process frequency and production yield. Here we report the detection of live interstellar 244Pu, archived in Earth’s deep-sea floor during the last 25 My, at abundances lower than expected from continuous production in the Galaxy by about 2 orders of magnitude. This large discrepancy may signal a rarity of actinide r-process nucleosynthesis sites, compatible with neutron-star mergers or with a small subset of actinide-producing supernovae.

The origin of heavy elements produced through rapid neutron capture ('r-process') by seed nuclei is one of the current nucleosynthesis mysteries [1][2][3] 19 as the mean value for stars in the Galactic disk, the total mass of heavy r-process elements (A ≥ 90) in the Galaxy is M tot,A≥90 ≈ 5 × 10 3 M . These elements show a consistent abundance pattern in metal-poor stars 18 , suggesting that they are produced in a single kind of event. The total mass yields a relation between the Galactic event rate, R, and the heavy r-process mass produced in each event M ej,A≥90 (see Fig. 1):Here R is the rate averaged over the age of the Galaxy and it is not necessarily the same as the present-day event rate R 0 . For sources related to the death of massive stars, the event rate should follow the star formation rate, which at present is lower than the average value 20 . For compact binary mergers, the event rate follows the star formation rate with some delay. The event rate of short gamma-ray bursts (SGRBs) (ref. 11) that probably arise from compact binary mergers 6 , increases with the cosmological redshift z at least up to z ≈ 0.8. In both cases, R 0 may be smaller than R by a factor of up to approximately five.Using the total mass alone we cannot distinguish between the high-rate/low-yield and the low-rate/high-yield sources.

Sons) Chichester, 1983. pp. 437; f35; paperback f12.95. This is the third edition of what has become the text-book on this very specialized field of meteorology. The first edition appeared in 1962 and was reviewed in this Journal by the late Sir Graham Sutton (88 (1962), p. 202). He wrote: "The book is not deep; it is obviously aimed more at the practising meteorologist and the engineer rather than at the mathematician and the theoretical physicist. In this limited field it succeeds admirably". Although I take issue with the implication by Sir Graham that a book cannot be 'deep' when it is aimed at the practising meteorologist, the statement about the aim is certainly correct. There was a second revised edition which was published in 1974 and for which-surprisingly enough-I could not find a review in the relevant journals.It is certainly interesting to compare the three editions which appeared in a time interval of roughly every 10 years and measure by this yardstick the evolution and progress in this field of atmospheric science. Whereas from the first to the second editionsmaller details omitted-only one new approach was included, which is the Lagrangian similarity treatment of diffusion in the surface layer, I found two new topics added in going from the second edition to the third: the similarity treatment of the mixed (or convective) boundary layer and the stochastic (Monte Carlo method) modelling of diffusion. It has also to be mentioned that the chapter on dispersion on the meso-and synoptic scale has been completely rewritten and reflects the latest developments.There has also been another, maybe more formal change between the second and third edition: whereas in the former editions Dr F. B. Smith was mentioned in the preface, he now acts as a co-author. From knowledge of Dr Smith's work I would assume that he is responsible for the chapters on stochastic modelling and on the meso-and synoptic-scale dispersion.The book is produced very nicely and has only a few printing errors. Remarkably enough there are three of them in four lines on p. 396. The graphs are well done and clear (in Fig. 2.14 the abscissa parameter should read A,,,/hc and in Fig. 2.15 a, instead of ow).The price of the book is modest by today's standards and one can recommend it strongly to anybody working in the field and to any newcomer. However, I would not advise a fourth edition-ven a revised one-but would rather like to see a new one, rewritten ab ovo. This book basically consists of a series of lectures presented at a NATO Advanced Study Institute held at the University of New Hampshire during July 1982, and is concerned with the transfer of gaseous, liquid and solid material, in either direction, across the air-sea interface. W. KLUGThe first three chapters deal with the fundamental aspects of the subject, commencing with an introduction to meteorology and fluid dynamics. This chapter begins with the basic physics of motion and goes on to describe large-and small-scale atmospheric flow, including flow close to solid and fluid int...

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Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust—iron-60 (60Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (244Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 million years and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.

Sm (25). We prepared spectroscopic alpha sources (20-100 μg) from the three activations and counted them during several months using a silicon surface-barrier detector at Kanazawa University (Fig. 1, 25 Galactic-disk enrichment in low-metallicity gas (Fig. 3). This reduces the age of late events (≥ 50 Ma) (age is measured in this work relative to the birth of the solar system) but has a minor effect on earlier events (Table 1). Samarium-146 observations in terrestrial samples can be divided into two groups: (i) most terrestrial rocks display a 142 Nd/ 144 Nd ratio higher by ~18 parts per million (ppm) than CHUR (9) and (ii) anomalies in the 142 Nd/ 144 Nd ratio relative to the terrestrial standard, both positive, in rocks from Greenland and Australia (2,10), and negative, in rocks from Northern Quebec (2,11).

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