Chicxulub's Impact Caused "Nuclear" Winter in New Jersey

Evidence for Cretaceous-Paleogene boundary bolide "impact winter" conditions from New Jersey, USA

Authors:

Vellekoop et al

Abstract:

Abrupt and short-lived "impact winter" conditions have commonly been implicated as the main mechanism leading to the mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (ca. 66 Ma), marking the end of the reign of the non-avian dinosaurs. However, so far only limited evidence has been available for such a climatic perturbation. Here we perform high-resolution TEX86 organic paleothermometry on three shallow cores from the New Jersey paleoshelf, (northeastern USA) to assess the impact-provoked climatic perturbations immediately following the K-Pg impact and to place these short-term events in the context of long-term climate evolution. We provide evidence of impact-provoked, severe climatic cooling immediately following the K-Pg impact. This so-called "impact winter" occurred superimposed on a long-term cooling trend that followed a warm phase in the latest Cretaceous.

No Further Impact Craters Greater Than 6 km Diameter Likely to be Found on Earth

The number of impact craters on Earth: Any room for further discoveries?

Authors:

Hergarten et al

Abstract:

Only 128 impact craters exposed at Earth's surface have been found so far, while new craters are discovered occasionally. Taking into account the permanent consumption of craters by erosion we present the first estimate on the number of impact craters that should be present at Earth's surface. Our study yields no evidence for any systematic incompleteness in the available inventory of the craters larger than about 6 km in diameter exposed at the surface. In contrast, more than 90 craters in the diameter range from 1 km to 6 km should still be waiting to be discovered, and even more than 250 between 0.25 km and 1 km diameter. The transition from a probably complete inventory above 6 km to a strongly incomplete record at smaller sizes may be related to the difference between simple and complex craters. Beyond these results on the terrestrial crater record, our findings tentatively suggest that erosion rates on the 10 to 100 million year scale may be closer to present-day erosion rates than previously assumed.

WHOA! Two Asteroid Impacts Caused Partial Ocean Evaporation During the PaleoArchean

Geologic record of partial ocean evaporation triggered by giant asteroid impacts, 3.29–3.23 billion years ago

Authors:

Lowe et al

Abstract:

Although lunar studies suggest that large asteroid impact rates in the inner solar system declined to their present low levels at 3.8–3.7 Ga, recent studies in greenstone belts indicate that asteroids 20 km to 70+ km in diameter were still striking the Earth as late as 3.2 Ga at rates significantly greater than the values estimated from lunar studies. We here present geologic evidence that two of these terrestrial impacts, at 3.29 Ga and 3.23 Ga, caused heating of Earth's atmosphere, ocean-surface boiling, and evaporation of tens of meters to perhaps 100 m of seawater. Rapid ocean evaporation resulted in abrupt sea-level drops, erosion of the exposed sea floor, and precipitation of distinctive layers of laminated silica representing marine siliceous sinter. Such events would have severely affected microbial communities, especially among shallow-water and photosynthetic organisms. These large impacts profoundly affected Archean crustal development, surface environment, and biological evolution until 3.2 Ga, or even later.

Sudbury Crater in Canada Confirmed to be Orosirian/Statherian Paleoproterozoic Cometary Impact

On the track of the elusive sudbury impact: geochemical evidence for a chondrite or comet bolide

Authors:

Petrus et al

Abstract:

Siderophile and lithophile trace element data for 69 samples from the Sudbury impact crater fill (Onaping Formation) and quartz diorite offset dikes help constrain the sources of the established moderately elevated platinum group element signature associated with the impact structure. The siderophile element distribution of the crater fill requires contributions from bulk continental crust, mafic rocks and a chondritic component. A mantle component is absent, but the involvement of mid to lower crust is implied. After considering post-impact hydrothermal alteration, melt heterogeneity, and mafic target admixture, the projectile elemental ratios were determined on a more robust data subset. Chondrite discrimination diagrams of these ratios identify an ordinary or enstatite chondrite as the most probable source of meteoritic material in the Sudbury crater fill. However, the relative and absolute siderophile element distributions within the impact structure as well as bolide size models are congruent with the bolide being a comet that had a chondritic refractory component.

Impacts Induced Martian Surface Heating?

Impact inducted surface heating by planetesimals on early Mars

Authors:

Maindl et al

Abstract:

We investigate the influence of impacts of large planetesimals and small planetary embryos on the early Martian surface on the hydrodynamic escape of an early steam atmosphere that is exposed to the high soft X-ray and EUV flux of the young Sun. Impact statistics in terms of number, masses, velocities, and angles of asteroid impacts onto the early Mars are determined via n-body integrations. Based on these statistics, smoothed particle hydrodynamics (SPH) simulations result in estimates of energy transfer into the planetary surface material and according surface heating. For the estimation of the atmospheric escape rates we applied a soft X-ray and EUV absorption model and a 1-D upper atmosphere hydrodynamic model to a magma ocean-related catastrophically outgassed steam atmosphere with surface pressure values of 52 bar H2O and 11 bar CO2. The estimated impact rates and energy deposition onto an early Martian surface can account for substantial heating. The energy influx and conversion rate into internal energy is most likely sufficient to keep a shallow magma ocean liquid for an extended period of time. Higher surface temperatures keep the outgassed steam atmosphere longer in vapor form and therefore enhance its escape to space within about 0.6 Myr after its formation.

First Evidence of Global Winter From Chicxulub Asteroid Impact

Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary

Authors:

Vellekoop et al

Abstract:

The mass extinction at the Cretaceous–Paleogene boundary, ∼66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called “impact winter” phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.

Using the Brazos River has got to cause Dr Keller some aggravation.

Alberta, Canada has a Younger Than 70 Million Year Old, 8 km Impact Crater

The discovery of an ancient ring-like structure in southern Alberta suggests the area was struck by a meteorite large enough to leave an eight-kilometre-wide crater, producing an explosion strong enough to destroy present-day Calgary, say researchers from the Alberta Geological Survey and University of Alberta.

The first hints about the impact site near the southern Alberta hamlet of Bow City were discovered by a geologist with the Alberta Geological Survey and studied by a U of A team led by Doug Schmitt, Canada Research Chair in Rock Physics.

Time and glaciers have buried and eroded much of the evidence, making it impossible at this point to say with full certainty the ring-like structure was caused by a meteorite impact, but that's what seismic and geological evidence strongly suggests, said Schmitt, a professor in the Faculty of Science and co-author of a new paper about the discovery.

"We know that the impact occurred within the last 70 million years, and in that time about 1.5 km of sediment has been eroded. That makes it really hard to pin down and actually date the impact."

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Microbial Trace Fossils in Impact Glass

Enigmatic tubular features in impact glass

Authors:

Sapers et al

Abstract:

We describe the first putative microbial trace fossils hosted in meteorite impact glass. We conducted optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy on postimpact tubular features hosted in impact glasses from the Ries impact structure (Germany). The morphologies of the tubules are inconsistent with known mineralogical crystallization mechanisms, and combined with evidence of organic molecules suggest that these tubules cannot be formed through purely abiotic processes. The simplest and most consistent explanation of the data is that biological activity played a role in the formation of the tubular textures in the Ries glasses, likely during postimpact hydrothermal activity. As impact glass is a ubiquitous substrate on rocky bodies throughout the Solar System and likely common on the early Earth, the preservation of biological activity in impact glass has significant astrobiological implications for life on early Earth as well as for the search for life on other planets.

Preserved Flora and Organics in Impact Remains

Preserved flora and organics in impact melt breccias

Authors:

Schtulz et al

Abstract:

Impact cratering can destroy life from local to global scales and result in sudden turnovers of dominant genera and/or species. Here we report that it can also preserve components of the local biology present at the time of impact. We have investigated floral matter encapsulated within Cenozoic Era impact glasses produced by separate bolide impacts into the loessoid sediments of Argentina that occurred between 9.2 Ma (Miocene) and 6 ka (Holocene). The encapsulation preserved not only macro-scale morphological biosignatures such as vascular bundles, veins, phytoliths, and papillae, but also structures down to the cellular level. In the best-preserved samples we also found evidence for organic matter. While fossilization typically occurs over an extended time period as minerals slowly replace organic matter and the host rock lithifies under pressure, the process documented here is instantaneous. Preservation of morphological and chemical biosignatures in impact events can provide snapshots of the ecology in environments that do not otherwise promote a diverse fossil record. We suggest that this would provide a new strategy for identifying signs of possible early life on ancient Mars, where similar target conditions once existed.

Just how big WAS the PaleoArchean Vredefort Impact?

A massive asteroid almost as wide as Rhode Island and about three to five times larger than the rock thought to have wiped out the dinosaurs slams into Earth. The collision punches a crater into the planet's crust that's nearly 500 kilometers (about 300 miles) across: greater than the distance from Washington, D.C. to New York City, and up to two and a half times larger in diameter than the hole formed by the dinosaur-killing asteroid. Seismic waves bigger than any recorded earthquakes shake the planet for about half an hour at any one location – about six times longer than the huge earthquake that struck Japan three years ago. The impact also sets off tsunamis many times deeper than the one that followed the Japanese quake.

Although scientists had previously hypothesized enormous ancient impacts, much greater than the one that may have eliminated the dinosaurs 65 million years ago, now a new study reveals the power and scale of a cataclysmic event some 3.26 billion years ago which is thought to have created geological features found in a South African region known as the Barberton greenstone belt. The research has been accepted for publication in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union.

The huge impactor – between 37 and 58 kilometers (23 to 36 miles) wide – collided with the planet at 20 kilometers per second (12 miles per second). The jolt, bigger than a 10.8 magnitude earthquake, propelled seismic waves hundreds of kilometers through the Earth, breaking rocks and setting off other large earthquakes. Tsunamis thousands of meters deep – far bigger than recent tsunamis generated by earthquakes -- swept across the oceans that covered most of the Earth at that time.

"We knew it was big, but we didn't know how big," Donald Lowe, a geologist at Stanford University and a co-author of the study, said of the asteroid.

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Was Acid Rain the Kill Mechanism of the KT/K-Pg Extinction Brought on by the Chicxulub Impact?

Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification

Authors:

Ohno et al

Abstract:

The mass extinction event at the Cretaceous/Palaeogene boundary 65.5 Myr ago has been widely attributed to the Chicxulub impact, but the mechanisms of extinction remain debated. In the oceans, near-surface planktonic foraminifera suffered severe declines, in contrast to the relatively high survival rates of bottom-dwelling benthic foraminifera. The vapour produced by an impact into Chicxulub’s target rocks, which include sulphate-rich anhydrite, could have led to global acid rain, which can explain the pattern of oceanic extinctions. However, it has been suggested that most of the sulphur in the target rocks would have been released as sulphur dioxide and would have stayed in the stratosphere for a long time. ere we show, from impact experiments into anhydrite at velocities exceeding 10 km s−1, that sulphur trioxide dominates over sulphur dioxide in the resulting vapour cloud. Our experiments suggest that the Chicxulub impact released a huge quantity of sulphur trioxide into the atmosphere, where it would have rapidly combined with water vapour to form sulphuric acid aerosol particles. We also find, using a theoretical model of aerosol coagulation following the Chicxulub impact, that larger silicate particles ejected during the impact efficiently scavenge sulphuric acid aerosol particles and deliver the sulphuric acid to the surface within a few days. The rapid surface deposition of sulphuric acid would cause severe ocean acidification and account for preferential extinction of planktonic over benthic foraminifera.

During the Late Hadean 3.9 Billion Years ago, Impacts Smashed, Repaved the World

The impact environment of the Hadean Earth

Authors:

Abramov et al

Abstract:

Impact bombardment in the first billion years of solar system history determined in large part the initial physical and chemical states of the inner planets and their potential to host biospheres. The range of physical states and thermal consequences of the impact epoch, however, are not well quantified. Here, we assess these effects on the young Earth's crust as well as the likelihood that a record of such effects could be preserved in the oldest terrestrial minerals and rocks. We place special emphasis on modeling the thermal effects of the late heavy bombardment (LHB) – a putative spike in the number of impacts at about 3.9 Gyr ago – using several different numerical modeling and analytical techniques. A comprehensive array of impact-produced heat sources was evaluated which includes shock heating, impact melt generation, uplift, and ejecta heating. Results indicate that ∼1.5–2.5 vol.% of the upper 20 km of Earth's crust was melted in the LHB, with only ∼0.3–1.5 vol.% in a molten state at any given time. The model predicts that approximately 5–10% of the planet's surface area was covered by less than 1 km deep impact melt sheets. A global average of ∼600–800 m of ejecta and ∼800–1000 m of condensed rock vapor is predicted to have been deposited in the LHB, with most of the condensed rock vapor produced by the largest (greater than 100-km) projectiles. To explore for a record of such catastrophic events, we created two- and three-dimensional models of post-impact cooling of ejecta and craters, coupled to diffusion models of radiogenic Pb*-loss in zircons. We used this to estimate what the cumulative effects of putative LHB-induced age resetting would be of Hadean zircons on a global scale. Zircons entrained in ejecta are projected to have the following average global distribution after the end of the LHB: ∼59% with no impact-induced Pb*-loss, ∼26% with partial Pb*-loss and ∼15% with complete Pb*-loss or destruction of the grain. In addition to the relatively high erodibility of ejecta, our results show that if discordant ca. 3.9 Gyr old zones in the Jack Hills zircons are a signature of the LHB, they were most likely sourced from impact ejecta.

Asteroids Show Solar System More Like a Snow Globe on Elvis (all Shook up)

Our solar system seems like a neat and orderly place, with small, rocky worlds near the Sun and big, gaseous worlds farther out, all eight planets following orbital paths unchanged since they formed.

However, the true history of the solar system is more riotous. Giant planets migrated in and out, tossing interplanetary flotsam and jetsam far and wide. New clues to this tumultuous past come from the asteroid belt.

"We found that the giant planets shook up the asteroids like flakes in a snow globe," says lead author Francesca DeMeo, a Hubble postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics.

Millions of asteroids circle the Sun between the orbits of Mars and Jupiter, in a region known as the main asteroid belt. Traditionally, they were viewed as the pieces of a failed planet that was prevented from forming by the influence of Jupiter's powerful gravity. Their compositions seemed to vary methodically from drier to wetter, due to the drop in temperature as you move away from the Sun.

That traditional view changed as astronomers recognized that the current residents of the main asteroid belt weren't all there from the start. In the early history of our solar system the giant planets ran amok, migrating inward and outward substantially. Jupiter may have moved as close to the Sun as Mars is now. In the process, it swept the asteroid belt nearly clean, leaving only a tenth of one percent of its original population.

As the planets migrated, they stirred the contents of the solar system. Objects from as close to the Sun as Mercury, and as far out as Neptune, all collected in the main asteroid belt.

"The asteroid belt is a melting pot of objects arriving from diverse locations and backgrounds," explains DeMeo.

Using data from the Sloan Digital Sky Survey, DeMeo and co-author Benoit Carry (Paris Observatory) examined the compositions of thousands of asteroids within the main belt. They found that the asteroid belt is more diverse than previously realized, especially when you look at the smaller asteroids.

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Extraordinary Claim: Chicxulub Impact Followed by Shiva Impact 40,000 Years Later

The Chicxulub-Shiva extraterrestrial one-two killer punches to Earth 65 million years ago

Author:

J.F. Lerbekmo

Abstract:

Two large asteroids struck Earth at almost the same time, 65 million years ago, causing the major extinctions recognized as ending the Mesozoic Era. Although occurring close together in time, the Earth's magnetic pole had moved from the South Pole to the North Pole in between, allowing a time difference between the impacts to be calculated. The first strike produced a ∼180 km diameter crater named Chicxulub on the Yucatan shelf of southern Mexico. The second hit the shelf of the northward drifting Indian continent in the southern Indian Ocean, producing a crater ∼450 × 600 km named Shiva. Hitherto, the main obstacle to verifying this scenario has been the paucity of geological sections containing evidence of both impacts. Here, we present such evidence, and conclude that the two impacts were separated by about 40,000 years.

Did an Impact Cause the Shuram Event in the Ediacaran by Shifting the Earth's Axis?

Evolution of Earth's climatic system: Evidence from ice ages, isotopes, and impacts

Author:

Grant M. Young

Abstract:

Multiple glaciations took place near the beginning and end of the Proterozoic Eon. Neoproterozoic (Cryogenian) glacial deposits are more widespread than those of older (Paleoproterozoic) glacial episodes. Paleomagnetic results suggest that most Proterozoic glaciogenic rocks were deposited at low paleolatitudes. Some contain enigmatic evidence of strong seasonal temperature variations, and many formed at sea level. These attributes inspired both the snowball Earth hypothesis and the high obliquity theory, but only the latter explains strong seasonality at low latitudes. The Proterozoic glaciations may have been triggered by drawdown of atmospheric CO2 during enhanced weathering of elevated supercontinents. Multiple glaciations resulted from a negative feedback loop in the weathering system that ended when the supercontinent broke apart. A radical reorganization of the climatic system took place in the Ediacaran Period. In contrast to previous glaciations, these ice sheets developed in high latitudes and many follow mountain building episodes. During the Ediacaran Period, Earth’s climatic zonation and controls appear to have undergone a radical change that persisted throughout the Phanerozoic Eon. The change may coincide with the world’s greatest negative δ13C excursion, the Shuram event, here interpreted as the result of a very large marine impact that decreased the obliquity of the ecliptic, causing the Earth’s climatic system to adopt its present configuration. Attendant unprecedented environmental reorganization may have played a crucial role in the emergence of complex life forms.

First Strong Evidence of Comet Impact in Rupelian/Chattian Oligocene Africa

The first ever evidence of a comet entering Earth's atmosphere and exploding, raining down a shock wave of fire which obliterated every life form in its path, has been discovered by a team of South African scientists and international collaborators.

The discovery has not only provided the first definitive proof of a comet striking Earth, millions of years ago, but it could also help us to unlock, in the future, the secrets of the formation of our solar system.

"Comets always visit our skies – they're these dirty snowballs of ice mixed with dust – but never before in history has material from a comet ever been found on Earth," says Professor David Block of Wits University.

The comet entered Earth's atmosphere above Egypt about 28 million years ago. As it entered the atmosphere, it exploded, heating up the sand beneath it to a temperature of about 2 000 degrees Celsius, and resulting in the formation of a huge amount of yellow silica glass which lies scattered over a 6 000 square kilometre area in the Sahara. A magnificent specimen of the glass, polished by ancient jewellers, is found in Tutankhamun's brooch with its striking yellow-brown scarab.

The research, which will be published in Earth and Planetary Science Letters, was conducted by a collaboration of geoscientists, physicists and astronomers including Block, lead author Professor Jan Kramers of the University of Johannesburg, Dr Marco Andreoli of the South African Nuclear Energy Corporation, and Chris Harris of the University of Cape Town.

At the centre of the attention of this team was a mysterious black pebble found years earlier by an Egyptian geologist in the area of the silica glass. After conducting highly sophisticated chemical analyses on this pebble, the authors came to the inescapable conclusion that it represented the very first known hand specimen of a comet nucleus, rather than simply an unusual type of meteorite.

Kramers describes this as a moment of career defining elation. "It's a typical scientific euphoria when you eliminate all other options and come to the realisation of what it must be," he said.

The impact of the explosion also produced microscopic diamonds. "Diamonds are produced from carbon bearing material. Normally they form deep in the earth, where the pressure is high, but you can also generate very high pressure with shock. Part of the comet impacted and the shock of the impact produced the diamonds," says Kramers.

The team have named the diamond-bearing pebble "Hypatia" in honour of the first well known female mathematician, astronomer and philosopher, Hypatia of Alexandria.

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Smoke/Vapor Trail From Chelyabinsk Impact Meteor Seen by Satellite

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Academic Bun Fight: Was There or Was There NOT an Impact at the Beginning of the Younger Dryas?

No:

Wittke et al. (1) present evidence of a major cosmic impact at the onset of the Younger Dryas (YD) episode, including some markers found in the top of the well-known Usselo marker horizon (UH). This finding is contrary to our extensive radiocarbon dating effort from this horizon (2), which shows that the UH at Aalsterhut postdates the onset of the YD. Furthermore, Wittke et al. (1) misinterpret the origin of the UH: this horizon is a well-defined paleosoil that formed during the Allerød and the early YD in the top part of coversand. This coversand was deposited before the Allerød, during cold and dry conditions, and is part of the European Sandbelt. Wildfires were common and occurred throughout this period, rather than synchronously with the onset of the YD (3).

Yes!

Van Hoesel et al. (1) refer to nanodiamonds at the top of the Usselo horizon at Aalsterhut, The Netherlands, having an average age of 10.845 ± 0.015 14C ka (12.70 ± 0.06 cal ka) (1); they found no nanodiamonds outside hat layer. Earlier, nanodiamonds were reported at the top of theUsselo in Lommel, Belgium,∼30 km southwest of Aalsterhut, acknowledged as the Younger Dryas boundary layer (YDB) [Tian et al. (2)]; those researchers also found no nanodiamonds outside that layer.

It all comes down to dating.

Evidence of a Large Impact in the Norian Triassic

Osmium isotope evidence for a large Late Triassic impact event

Authors:

1. Honami Sato (a)
2. Tetsuji Onoue (a)
3. Tatsuo Nozaki (b)
4. Katsuhiko Suzuki (b)

Affiliations:

a. Department of Earth and Environmental Sciences, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan

b. Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

Abstract:

Anomalously high platinum group element concentrations have previously been reported for Upper Triassic deep-sea sediments, which are interpreted to be derived from an extraterrestrial impact event. Here we report the osmium (Os) isotope fingerprint of an extraterrestrial impact from Upper Triassic chert successions in Japan. Os isotope data exhibit a marked negative excursion from an initial Os isotope ratio (187Os/188Osi) of ~0.477 to unradiogenic values of ~0.126 in a platinum group element-enriched claystone layer, indicating the input of meteorite-derived Os into the sediments. The timing of the Os isotope excursion coincides with both elevated Os concentrations and low Re/Os ratios. The magnitude of this negative Os isotope excursion is comparable to those found at Cretaceous–Paleogene boundary sites. These geochemical lines of evidence demonstrate that a large impactor (3.3–7.8 km in diameter) produced a global decrease in seawater 187Os/188Os ratios in the Late Triassic.

Darmouth Group Finds Evidence of Younger Dryas Impact

The impact occurred about 12,900 years ago, at the beginning of the Younger Dryas period, and marks an abrupt global change to a colder, dryer climate with far-reaching effects on both animals and humans. In North America, the big animals all vanished, including mastodons, camels, giant ground sloths and saber-toothed cats. Their human hunters, known to archaeologists as the Clovis people, set aside their heavy-duty spears and turned to a hunter-gatherer subsistence diet of roots, berries and smaller game.

It is not disputed that these powerful environmental changes occurred, but there has long been controversy over their cause. The classic view of the Younger Dryas cooling interlude has been that an ice dam in the North American ice sheet ruptured, releasing a massive quantity of freshwater into the Atlantic Ocean. The sudden influx is thought to have shut down the ocean currents that move tropical water northward, resulting in the cold, dry climate of the Younger Dryas.

But Sharma and his co-authors have discovered conclusive evidence linking an extraterrestrial impact with this environmental transformation. The report focuses on spherules, or droplets of solidified molten rock expelled by the impact of a comet or meteor. The spherules in question were recovered from Younger Dryas boundary layers at sites in Pennsylvania and New Jersey, the layers having been deposited at the beginning of the period. The geochemistry and mineralogy profiles of the spherules are identical to rock found in southern Quebec, where Sharma and his colleagues argue the impact took place.

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