During 2003-2008. A group of Russian and Austrian scientists with the participation of Heinz Kohlmann, a renowned paleontologist, curator of the Eisenwurzen National Park, studied the catastrophe that happened 65 million years ago, when more than 75% of all organisms on Earth, including dinosaurs, died out. Most researchers believe that the extinction was associated with an asteroid impact, although there are other points of view
Traces of this catastrophe in geological sections are represented by a thin layer of black clay 1 to 5 cm thick. One of these sections is located in Austria, in the Eastern Alps, in the National Park near the small town of Gams, located 200 km south-west of Vienna. As a result of studying samples from this section using a scanning electron microscope, particles of unusual shape and composition were found, which do not form under ground conditions and are classified as cosmic dust.
Stardust on Earth
For the first time, traces of space matter on Earth were discovered in red deep-sea clays by an English expedition that explored the bottom of the World Ocean on the Challenger ship (1872–1876). They were described by Murray and Renard in 1891. At two stations in the South Pacific Ocean, when dredging from a depth of 4300 m, samples of ferromanganese nodules and magnetic microspheres up to 100 µm in diameter were recovered, later called "space balls." However, the details of the iron microspheres raised by the Challenger expedition have been investigated only in recent years. It turned out that the balls are 90% metallic iron, 10% nickel, and their surface is covered with a thin crust of iron oxide.
Figure: 1. Monolith from the Gams 1 section, prepared for sampling. Layers of different ages are indicated in Latin letters. The transitional layer of clay between the Cretaceous and Paleogene periods (age about 65 million years), in which an accumulation of metal microspheres and plates was found, is marked with the letter "J". Photo by A. F. Gracheva
The discovery of mysterious balls in deep-sea clays, in fact, is associated with the beginning of the study of cosmic matter on Earth. However, an explosion of interest among researchers in this problem occurred after the first launches of spacecraft, with the help of which it became possible to select lunar soil and samples of dust particles from different parts of the solar system. The works of K. P. Florensky (1963), who studied the traces of the Tunguska catastrophe, and E. L. Krinov (1971), who studied meteoric dust at the site of the fall of the Sikhote-Alin meteorite.
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The interest of researchers in metal microspheres led to the fact that they began to be found in sedimentary rocks of different ages and origins. Metal microspheres are found in the ice of Antarctica and Greenland, in deep ocean sediments and manganese nodules, in the sands of deserts and coastal beaches. They are often found in and around meteorite craters.
In the last decade, metal microspheres of extraterrestrial origin have been found in sedimentary rocks of different ages: from the Lower Cambrian (about 500 million years ago) to modern formations.
Data on microspheres and other particles from ancient sediments make it possible to judge the volumes, as well as the uniformity or unevenness of the influx of cosmic matter to the Earth, the change in the composition of particles arriving to the Earth from space, and the primary sources of this substance. This is important because these processes affect the development of life on Earth. Many of these questions are still far from being resolved, but the accumulation of data and their comprehensive study will undoubtedly make it possible to answer them.
It is now known that the total mass of dust circulating inside the earth's orbit is about 1015 tons. From 4 to 10 thousand tons of cosmic matter falls on the Earth's surface annually. 95% of the matter falling on the Earth's surface is made up of particles 50–400 microns in size. The question of how the rate of entry of cosmic matter to Earth changes over time remains controversial until now, despite many studies carried out in the past 10 years.
Based on the size of cosmic dust particles, at present, the actual interplanetary cosmic dust is emitted with a size less than 30 microns and micrometeorites larger than 50 microns. Even earlier E. L. Krinov proposed to call the smallest fragments of a meteoric body melted from the surface micrometeorites.
Strict criteria for distinguishing cosmic dust and meteorite particles have not yet been developed, and even using the example of the Gams section studied by us, it has been shown that metal particles and microspheres are more diverse in shape and composition than provided for by the existing classifications. The almost perfect spherical shape, metallic luster and magnetic properties of the particles were considered as evidence of their cosmic origin. According to the geochemist E. V. Sobotovich, "the only morphological criterion for assessing the cosmogeneity of the material under study is the presence of fused balls, including magnetic ones." However, in addition to the form, which is extremely diverse, the chemical composition of the substance is fundamentally important. The researchers found outthat along with microspheres of cosmic origin, there is a huge number of balls of a different genesis - associated with volcanic activity, the vital activity of bacteria or metamorphism. It is known that ferruginous microspheres of volcanogenic origin are much less often of ideal spherical shape and, moreover, have an increased admixture of titanium (Ti) (more than 10%).
A Russian-Austrian group of geologists and a film crew from Vienna TV at the Gams section in the Eastern Alps. In the foreground - A. F. Grachev
The origin of cosmic dust
The origin of cosmic dust is still under discussion. Professor E. V. Sobotovich believed that cosmic dust could be the remnants of the original protoplanetary cloud, which B. Yu. Levin and A. N. Simonenko, believing that fine matter could not persist for a long time (Earth and Universe, 1980, No. 6).
There is another explanation: the formation of cosmic dust is associated with the destruction of asteroids and comets. As noted by E. V. Sobotovich, if the amount of cosmic dust entering the Earth does not change over time, then B. Yu. Levin and A. N. Symonenko.
Despite the large number of studies, the answer to this fundamental question cannot be given at present, because there are very few quantitative estimates, and their accuracy is controversial. Recently, data from isotope studies under the NASA program of cosmic dust particles sampled in the stratosphere suggest the existence of particles of pre-solar origin. In the composition of this dust, minerals such as diamond, moissanite (silicon carbide) and corundum were found, which, based on the isotopes of carbon and nitrogen, make it possible to attribute their formation to the time before the formation of the solar system.
The importance of studying cosmic dust in a geological section is obvious. This article presents the first results of the study of space matter in the transitional clay layer at the Cretaceous-Paleogene boundary (65 million years ago) from the Gams section, in the Eastern Alps (Austria).
General characteristics of the Gams section
Particles of cosmic origin were obtained from several sections of the transitional layers between the Cretaceous and the Paleogene (in the Germanic literature - the K / T boundary), located near the alpine village of Gams, where the river of the same name in several places opens this boundary.
In the Gams 1 section, a monolith was cut from the outcrop, in which the K / T boundary is very well expressed. Its height is 46 cm, width - 30 cm in the lower part and 22 cm - in the upper part, thickness - 4 cm. For a general study of the section, the monolith was divided after 2 cm (from bottom to top) into layers designated by letters of the Latin alphabet (A, B, C… W), and within each layer, also after 2 cm, marking with numbers (1, 2, 3, etc.) is carried out. The transitional layer J at the K / T interface was studied in more detail, where six sublayers with a thickness of about 3 mm were distinguished.
The research results obtained in the Gams 1 section were largely repeated when studying another section - Gams 2. The complex of studies included the study of thin sections and monomineral fractions, their chemical analysis, as well as X-ray fluorescence, neutron-activation and X-ray structural analyzes, isotopic analysis of helium, carbon and oxygen, determination of the composition of minerals on a microprobe, magnetomineralogical analysis.
Variety of microparticles
Iron and nickel microspheres from the transitional layer between the Cretaceous and Paleogene in the Gams section: 1 - Fe microsphere with a coarse reticular-knobby surface (upper part of the transitional layer J); 2 - Fe microsphere with a rough longitudinally parallel surface (lower part of the transition layer J); 3 - Fe microsphere with crystallographic faceting elements and a coarse mesh-like surface texture (layer M); 4 - Fe microsphere with a thin mesh surface (upper part of the transition layer J); 5 - Ni microsphere with crystallites on the surface (upper part of the transition layer J); 6 - aggregate of sintered Ni microspheres with crystallites on the surface (upper part of the transition layer J); 7 - aggregate of Ni microspheres with microdiamonds (C; upper part of the transition layer J); 8,9 - characteristic forms of metal particles from the transitional layer between Cretaceous and Paleogene in the Gams section in the Eastern Alps.
In the transitional layer of clay between the two geological boundaries - Cretaceous and Paleogene, as well as at two levels in the overlying sediments of the Paleocene in the Gams section, many metal particles and microspheres of cosmic origin were found. They are much more diverse in shape, surface texture and chemical composition than all known so far in the transitional clay layers of this age in other regions of the world.
In the Gams section, space matter is represented by finely dispersed particles of various shapes, among which the most common are magnetic microspheres ranging in size from 0.7 to 100 μm, consisting of 98% pure iron. Such particles in the form of spheres or microspherules are found in large numbers not only in layer J, but also above, in clays of the Paleocene (layers K and M).
Microspheres are composed of pure iron or magnetite, some of which contain chromium (Cr), an alloy of iron and nickel (avaruite), and pure nickel (Ni). Some Fe-Ni particles contain molybdenum (Mo) impurities. In the transitional layer of clay between the Cretaceous and Paleogene, they were all discovered for the first time.
Never before have we come across particles with a high nickel content and a significant admixture of molybdenum, microspheres with the presence of chromium and pieces of spiral iron. In addition to metal microspheres and particles, Ni-spinel, microdiamonds with microspheres of pure Ni, as well as torn plates of Au, Cu, which are not found in the underlying and overlying deposits, were found in the transitional clay layer in Gams.
Characteristics of microparticles
Metallic microspheres in the Gams section are present at three stratigraphic levels: ferruginous particles of various shapes are concentrated in the transitional clay layer, in the overlying fine-grained sandstones of the K layer, and the third level is formed by siltstones of the M layer.
Some spheres have a smooth surface, others have a lattice-knobby surface, while others are covered with a mesh of small polygonal or a system of parallel cracks extending from one main crack. They are hollow, shell-like, filled with clay minerals, and may also have an internal concentric structure. Fe metal particles and microspheres are found throughout the transitional clay layer, but are mainly concentrated in the lower and middle horizons.
Micrometeorites are fused particles of pure iron or an iron-nickel alloy Fe-Ni (avaruite); their sizes are from 5 to 20 microns. Numerous avaruite particles are confined to the upper level of the transitional layer J, while pure ferruginous particles are present in the lower and upper parts of the transitional layer.
Particles in the form of plates with a cross-tuberous surface consist only of iron, their width is 10–20 µm, and their length is up to 150 µm. They are slightly arcuate and meet at the base of the transition layer J. In its lower part, Fe-Ni plates with an admixture of Mo are also encountered.
Plates of an alloy of iron and nickel have an elongated shape, slightly curved, with longitudinal grooves on the surface, the dimensions vary in length from 70 to 150 µm with a width of about 20 µm. They are more common in the lower and middle parts of the transitional layer.
Ferruginous plates with longitudinal grooves are identical in shape and size to Ni-Fe alloy plates. They are confined to the lower and middle parts of the transitional layer.
Particles of pure iron, which have the shape of a regular spiral and are bent in the form of a hook, are of particular interest. They are mainly composed of pure Fe, rarely Fe-Ni-Mo alloy. Coiled iron particles are found in the upper part of the J layer and in the overlying sandstone interlayer (K layer). A helical Fe-Ni-Mo particle was found at the base of the transition layer J.
In the upper part of the transition layer J, there were several grains of microdiamonds sintered with Ni microspheres. Microprobe studies of nickel balls, carried out on two instruments (with wave and energy dispersive spectrometers), showed that these balls consist of almost pure nickel under a thin film of nickel oxide. The surface of all nickel balls is dotted with clear crystallites with pronounced twins 1–2 µm in size. Such pure nickel in the form of spheres with a well-crystallized surface is not found either in igneous rocks or in meteorites, where nickel necessarily contains a significant amount of impurities.
When studying the monolith from the Gams 1 section, balls of pure Ni were found only in the uppermost part of the transitional layer J (in its uppermost part - a very thin sedimentary layer J6, the thickness of which does not exceed 200 μm), and according to the data of thermal magnetic analysis, metallic nickel is present in transition layer, starting with sublayer J4. Here, along with Ni balls, diamonds were also found. In a layer removed from a cube with an area of 1 cm2, the number of found diamond grains is in the tens (with a size from fractions of microns to tens of microns), and nickel balls of the same size - in hundreds.
In samples from the upper part of the transition layer taken directly from the outcrop, diamonds with fine nickel particles on the grain surface were found. It is significant that when studying samples from this part of layer J, the presence of the mineral moissanite was also revealed. Earlier, microdiamonds were found in the transitional layer at the Cretaceous-Paleogene boundary in Mexico.
Finds in other areas
The Gams microspheres with a concentric internal structure are similar to those that were mined by the Challenger expedition in the deep-sea clays of the Pacific Ocean.
Iron particles of irregular shape with melted edges, as well as in the form of spirals and curved hooks and plates are very similar to the products of destruction of meteorites falling to the Earth, they can be considered as meteoric iron. Particles of avaruite and pure nickel can be assigned to the same category.
Curved iron particles are close to various forms of Pele tears - lava drops (lapilli), which volcanoes eject from the vent during eruptions in a liquid state.
Thus, the transitional clay layer at Gams has a heterogeneous structure and is clearly subdivided into two parts. In the lower and middle parts, iron particles and microspheres prevail, while the upper part of the layer is enriched with nickel: avaruite particles and nickel microspheres with diamonds. This is confirmed not only by the distribution of iron and nickel particles in the clay, but also by the data of chemical and thermomagnetic analyzes.
Comparison of the data of thermomagnetic analysis and microprobe analysis indicates an extreme heterogeneity in the distribution of nickel, iron, and their alloy within the J layer; however, according to the results of thermomagnetic analysis, pure nickel is recorded only from the J4 layer. Noteworthy is the fact that helical iron occurs mainly in the upper part of the J layer and continues to occur in the overlying K layer, where, however, there are few isometric or lamellar Fe, Fe-Ni particles.
We emphasize that such a clear differentiation in iron, nickel, and iridium, manifested in the transitional clay layer in Gams, is also present in other regions. For example, in the US state of New Jersey, in the transitional (6 cm) spherulic layer, the iridium anomaly sharply manifested itself at its base, and impact minerals are concentrated only in the upper (1 cm) part of this layer. In Haiti, at the Cretaceous-Paleogene boundary and in the uppermost part of the spherul layer, there is a sharp enrichment in Ni and shock quartz.
Background phenomenon for Earth
Many features of the found Fe and Fe-Ni spherules are similar to the balls discovered by the Challenger expedition in the deep-sea clays of the Pacific Ocean, in the area of the Tunguska catastrophe and the fall sites of the Sikhote-Alin meteorite and Nio meteorite in Japan, as well as in sedimentary rocks of various ages from many areas of the world. In addition to the regions of the Tunguska catastrophe and the fall of the Sikhote-Alin meteorite, in all other cases the formation of not only spherules, but also particles of various morphologies, consisting of pure iron (sometimes with a chromium content) and an alloy of nickel with iron, has no connection with the impact event. We consider the appearance of such particles as a result of cosmic interplanetary dust falling onto the Earth's surface - a process that has been continuously going on since the formation of the Earth and is a kind of background phenomenon.
Many particles studied in the Gams section are close in composition to the gross chemical composition of the meteorite matter at the site of the fall of the Sikhote-Alin meteorite (according to E. L. Krinov, this is 93.29% iron, 5.94% nickel, 0.38% cobalt).
The presence of molybdenum in some of the particles is not unexpected as it includes many types of meteorites. The content of molybdenum in meteorites (iron, stone and carbonaceous chondrites) ranges from 6 to 7 g / t. The most important was the find of molybdenite in the Allende meteorite in the form of an inclusion in the alloy of the following metal composition (wt%): Fe - 31.1, Ni - 64.5, Co - 2.0, Cr - 0.3, V - 0.5, P - 0.1. It should be noted that native molybdenum and molybdenite were also found in lunar dust sampled by the automatic stations Luna-16, Luna-20, and Luna-24.
The first discovered spheres of pure nickel with a well-crystallized surface are not known either in igneous rocks or in meteorites, where nickel necessarily contains a significant amount of impurities. Such a structure of the surface of nickel balls could arise in the event of an asteroid (meteorite) falling, which led to the release of energy, which made it possible not only to melt the material of the falling body, but also to evaporate it. The metal vapors could have been lifted by the explosion to a great height (probably tens of kilometers), where crystallization took place.
Particles composed of avaruite (Ni3Fe) are found together with metallic balls of nickel. They belong to meteoric dust, and fused iron particles (micrometeorites) should be considered as "meteorite dust" (in the terminology of EL Krinov). The diamond crystals encountered along with nickel balls probably arose as a result of ablation (melting and evaporation) of a meteorite from the same vapor cloud during its subsequent cooling. It is known that synthetic diamonds are obtained by spontaneous crystallization from a carbon solution in a metal melt (Ni, Fe) above the graphite-diamond phase equilibrium line in the form of single crystals, their intergrowths, twins, polycrystalline aggregates, frame crystals, needle-shaped crystals, irregular grains. Almost all of the listed typomorphic features of diamond crystals were found in the sample under study.
This allows us to conclude that the processes of diamond crystallization in a cloud of nickel-carbon vapor during its cooling and spontaneous crystallization from a carbon solution in a nickel melt in experiments are similar. However, the final conclusion about the nature of diamond can be made after detailed isotopic studies, for which it is necessary to obtain a sufficiently large amount of substance.
Thus, the study of space matter in the transitional clayey layer at the Cretaceous-Paleogene boundary showed its presence in all parts (from layer J1 to layer J6), but signs of an impact event are recorded only from layer J4, which is 65 million years old. This layer of cosmic dust can be compared with the death of the dinosaurs.
