The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
The idea that life began elsewhere and then naturally migrated to the Earth is known as Panspermia. One such possibility is that life is carried on objects (meteorites, comets and dust) that arrive at the Earth. The life (bacteria) is then presumed to survive the sudden deceleration and impact, and then subsequently develop here on Earth. This step, the survivability of bacteria during the deceleration...
In the early solar system, the impact of comets, asteroids and micrometeorites on the primitive Earth resulted in extraterrestrial organic matter reaching the planet surface intact. This organic matter contributed to the organic inventory available for chemical reactions on the early Earth and may have played a role in the origin of life. Carbonaceous chondrites contain up to 5% by weight of...
Since micrometeorites may have played an important role in the development of conditions on the early Earth, bringing vital supplies of the biogenically important elements, it is apposite to appraise the effects that atmospheric heating exerts on such particles as they head towards the planet's surface. An expedient way to approach this problem is to undertake an investigation of the effects of pulse-heating...
The Moon was subjected to intense post-accretionary bombardment between about 4.5 and 3.9 billion years ago, and there is evidence for a short and intense late heavy bombardment period, around 3.85 ± 0.05 Ga. If a late heavy bombardment occurred on the Moon, the Earth must have been subjected to an impact flux at least as intense. The consequences for the Earth must have been devastating. In an attempt...
The chromium isotopic compositions of samples from an early Archean (3.22 Ga) spherule bed (S4) from the Barberton Greenstone Belt, South Africa, are distinct from that in background rocks and other terrestrial samples. This positively confirms the presence of an extraterrestrial component in this bed and supports hypotheses of an impact origin. The source of the extraterrestrial Cr is most likely...
The origin of multiple spherule-rich layers of millimeter to meter width, all occurring within the transition from the Fig Tree to the Onverwacht Group of the Barberton Greenstone Belt in South Africa, has been strongly debated during the last decade. One school subscribes to an origin by large meteorite impact, whereas others have preferred terrestrial processes. In particular, strong enrichments...
In addition to craters and related structures, large impacts may create strewn fields of ejecta that have the potential to be incorporated into the stratigraphic record. Nine layers rich in sand-size spherules of former silicate melt interpreted as impact ejecta have been reported from early Archean to early Paleoproterozoic successions. The layer in the late Archean Carawine Dolomite (Western Australia)...
The oldest known micrometeorites occur in the up to 1800 m thick Mesoproterozoic Satakunta sandstone in SW-Finland. This typical red bed formation covers a graben with the dimensions of about 15 × 100 km2. The Satakunta formation correlates with the Jotnian sandstone, overlaying at several locations in Fennoscandia basement rocks, which are part of the about 1.8 to 1.9 Ga old Svecofennian orogenic...
Pre-Cambrian shields and platforms occupy a large part of the Earth's continental surface. The crystalline rocks of these megastructures are the result of intense metamorphic, igneous and tectonic transformations. It is often difficult to recognize evidence of the past sedimentary, volcanic and igneous activities here. Even more problematic is the identification of old impact structures within Pre-Cambrian...
The main evidence in the Vredefort Dome and surrounding parts of the Witwatersrand Basin is presented, which indicates that this terrain represents the deeply exhumed root zone of a large, 2023 ± 4 Ma, complex impact structure. Shock metamorphic features such as impact melt, shatter cones, high-pressure quartz polymorphs and shock microdeformation features are restricted to the Vredefort Dome, which...
Ancient impact craters are commonly deeply eroded, metamorphosed and/or deformed by later tectonics. The identification of such impact structures using microstructural or mineralogical criteria are very difficult to apply under such conditions. It is proposed that fault patterns in the crater basement can be used diagnostically in eroded structures. On the basis of field observations in the Rochechouart...
Orbital remote sensing has discovered a number of impact structures on Earth. Complex structures eroded below allochthonous breccias and sheets of impact melt typically reveal a multicircular bull‘s-eye pattern when the projectile struck a subhorizontally bedded sedimentary target. These structures are striking because of steeply dipping strata in the central uplift, sometimes encircling a crystalline...
The rate at which the surface of Earth is being cratered can be measured by analyzing the sizes and ages of the craters that are found on certain stable areas of the Earth's landmass. It is shown, over the range 2.5 < D < 100 km, that the number N(D) of craters that are formed per unit area per unit time larger than diameter D does not (as previously thought) follow a simple relationship of...
We have recently interpreted distinctive feathery-textured “spinifex” carbonate in the upper part of the Chicxulub suevite breccia as quenched carbonate melts (Jones et al. 1998); these distinctive fragments make up to ∼10 vol% of the breccia. Carbonate clasts and spherules occurring in the ejecta-rich basal part of the coarse clastic sequence, which marks the K/T boundary all around the Gulf of Mexico,...
Rocks, interpreted as impact generated lithologies, occur in a large area surrounding the Gallejaur magnetic structure at latitude 65°10′/longitude 19°30′ in northernmost Västerbotten County in northern Sweden. These rocks comprise a variety of different types of breccias: authigenic/autochthonous monomict breccias from the underlying rock units (monomictly brecciated basement), parautochthonous,...
The Neugrund Bank is situated on the southern side of the entrance of the Gulf of Finland (59°20′N; 23°31′E) between Osmussaar and Krass islands. It is a shoal of a very peculiar multi-ring shape. In the coastal and offshore area of North-Western Estonia, numerous erratic boulders, consisting of rocks resembling impact breccias, have been found. The investigations proved that under Neugrund Bank and...
The 4-km-wide and 0.5-km-deep Kärdla Crater, presently buried under a thin sequence of Upper Ordovician limestone, was formed in a complex target: the crystalline basement was covered by about 170 m of poorly consolidated Lower to Middle Ordovician and Cambrian sediments. The basement-derived granitoids and amphibolites that were subjected to low shock pressure (less than 8 GPa) and are at present...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.