Airbursts/impacts by a fragmented comet or asteroid have been proposed at the Younger Dryas onset (12.80 ± 0.15 ka) based on identification of an assemblage of impact-related proxies, including microspherules, nanodiamonds, and iridium. Distributed across four continents at the Younger Dryas boundary (YDB), spherule peaks have been independently confirmed in eight studies, but unconfirmed in two others, resulting in continued dispute about their occurrence, distribution, and origin. To further address this dispute and better identify YDB spherules, we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry, morphologies, origins, and processes of formation. We investigated 18 sites across North America, Europe, and the Middle East, performing nearly 700 analyses on spherules using energy dispersive X-ray spectroscopy for geochemical analyses and scanning electron microscopy for surface microstructural characterization. Twelve locations rank among the world's premier end-Pleistocene archaeological sites, where the YDB marks a hiatus in human occupation or major changes in site use. Our results are consistent with melting of sediments to temperatures >2,200°C by the thermal radiation and air shocks produced by passage of an extraterrestrial object through the atmosphere; they are inconsistent with volcanic, cosmic, anthropogenic, lightning, or authigenic sources. We also produced spherules from wood in the laboratory at >1,730°C, indicating that impactrelated incineration of biomass may have contributed to spherule production. At 12.8 ka, an estimated 10 million tonnes of spherules were distributed across ∼50 million square kilometers, similar to well-known impact strewnfields and consistent with a major cosmic impact event.Clovis-Folsom | lechatelierite | tektite | wildfires

It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica-and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum, mullite, and suessite (Fe 3 Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO 2 glass, or lechatelierite, with flow textures (or schlieren) that form at >2,200°C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistent with cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.tektite | microcraters | oxygen fugacity | trinitite Manuscript TextThe discovery of anomalous materials in a thin sedimentary layer up to a few cm thick and broadly distributed across several continents led Firestone et al. (1) to propose that a cosmic impact (note that "impact" denotes a collision by a cosmic object either with Earth's surface, producing a crater, or with its atmosphere, producing an airburst) occurred at 12.9 kiloannum (ka; all dates are in calendar or calibrated ka, unless otherwise indicated) near the onset of the Younger Dryas (YD) cooling episode. This stratum, called the YD boundary layer, or YDB, often occurs directly beneath an organic-rich layer, referred to as a black mat (2), that is distributed widely over North America and parts of South America, Europe, and Syria. Black mats also occur less frequently in quaternary deposits that are younger and older than 12.9 ka (2). The YDB layer contains elevated abundances of iron-and silica-rich microspherules (collectively called "spherules") that are interpreted to have originated by cosmic impact because of their unique properties, as discussed below. Other markers include sediment and magnetic grains with elevated iridium concentrations and exot...

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On 16 July 1945, the first atomic bomb was detonated at the Alamogordo Bombing range in New Mexico, USA. Swept up into the nuclear cloud was the surrounding desert sand, which melted to form a green glassy material called 'trinitite'. Contained within the glass are melted bits of the first atomic bomb and the support structures and various radionuclides formed during the detonation. The glass itself is marvelously complex at the tens to hundreds of micrometre scale, and besides glasses of varying composition also contains unmelted quartz grains. Air transport of the melted material led to the formation of spheres and dumbbell shaped glass particles. Similar glasses are formed during all ground level nuclear detonations and contain forensic information that can be used to identify the atomic device.At 05:29:45 am local time on Monday, 16 July 1945, the nuclear age began. In a most graphic example of Einstein's famous equation (E = mc 2 or the original form m = L/V 2 where L = mass and V = the speed of light) a plutonium bomb, referred to as the 'Gadget', with a yield of 21 kilotons (equivalent to the explosive power of 21 000 tons of TNT) was detonated ( Fig. 1) at the Alamogordo Bombing range, 210 miles south of Los Alamos, New Mexico. The genie was out of the bottle and has been our uneasy companion ever since. One of the products of this nuclear explosion was a green glassy material formed by melting of the surrounding desert sand. Robert Oppenheimer had chosen the name 'Trinity' for the nuclear test and the name 'trinitite' was adopted for this green glassy material. The nuclear explosionThere are two fissionable isotopes (U-235 and Pu-239) that can be used to make atomic (fission) bombs. In both cases the basic principle is the same. A neutron interacts with a nucleus which leads to an increase in atomic mass and an unstable nucleus that splits into several pieces (fission fragments) + neutrons with a concomitant release in energy due to a loss in mass. The 235 U fission reaction is: U-235 + neutron → U-236 → fission fragments + neutrons + energyThe ejected neutrons cause further fission events leading to a chain reaction. For an explosive nuclear reaction billions of fission events need to occur in microseconds. The key is to have a sufficient mass of U-235 or Pu-239 in close proximity for this explosive reaction to occur.Two types of nuclear weapons were developed near the end of World War II. One, the 'gun type' consisted of an enriched uranium (U-235) bullet that was fired at an enriched uranium spike. The impact of these two pieces of enriched uranium produced the necessary mass density for a thermal nuclear explosion. Physicists were convinced that this type of bomb would work and only one was built and subsequently dropped on Hiroshima, on 6 August 1945. Fig. 1. The only known colour photograph of the Trinity Test.

At present, the worldwide captive elephant population is not self‐sustaining. The major reason for low reproductive rates is the heretofore undiagnosed reproductive disorders of nulliparous females of prime breeding age. Recent advances in ultrasound technology have facilitated the detection of these disorders in non‐sedated animals. Approximately 2,000 ultrasonographic examinations were performed in more than 280 captive and wild African and captive Asian female elephants. The entire urogenital tract was scanned, measured, and documented to provide a reference for ultrasound specialists involved in elephant breeding programs. The primary pathological lesions that influenced reproductive rates in these females were uterine tumors and endometrial cysts and ovarian cysts that resulted in acyclicity. The detection of these disorders and their stage of development can be used by elephant managers to make decisions approximately which animals to include in breeding programs. Ultrasonography can be used as an effective tool for assessing the reproductive fitness of female breeding candidates in both African and Asian elephants. Zoo Biol 19:321–332, 2000. © 2000 Wiley‐Liss, Inc.

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The northern white rhinoceros (NWR, Ceratotherium simum cottoni) is the most endangered mammal in the world with only two females surviving. Here we adapt existing assisted reproduction techniques (ART) to fertilize Southern White Rhinoceros (SWR) oocytes with NWR spermatozoa. We show that rhinoceros oocytes can be repeatedly recovered from live SWR females by transrectal ovum pick-up, matured, fertilized by intracytoplasmic sperm injection and developed to the blastocyst stage in vitro. Next, we generate hybrid rhinoceros embryos in vitro using gametes of NWR and SWR. We also establish embryonic stem cell lines from the SWR blastocysts. Blastocysts are cryopreserved for later embryo transfer. Our results indicate that ART could be a viable strategy to rescue genes from the iconic, almost extinct, northern white rhinoceros and may also have broader impact if applied with similar success to other endangered large mammalian species.

ZOO Dvůr Kr alov e, Dvůr Kr alov e nad Labem, Czech RepublicWith only three living individuals left on this planet, the northern white rhinoceros (Ceratotherium simum cottoni) could be considered doomed for extinction. It might still be possible, however, to rescue the (sub)species by combining novel stem cell and assisted reproductive technologies. To discuss the various practical options available to us, we convened a multidisciplinary meeting under the name "Conservation by Cellular Technologies." The outcome of this meeting and the proposed road map that, if successfully implemented, would ultimately lead to a self-sustaining population of an extremely endangered species are outlined here. The ideas discussed here, while centered on the northern white rhinoceros, are equally applicable, after proper adjustments, to other mammals on the brink of extinction. Through implementation of these ideas we hope to establish the Conflicts of interest: None.Oliver A. Ryder and Thomas B. Hildebrandt are of equal seniority.Co-authors, other than first and the two senior authors, are listed by alphabetical order.