How can meteorites cause catastrophic extinction

Indiana University Press: The views expressed are those of the author s and are not necessarily those of Scientific American. My name is David Bressan and I'm a freelance geologist working mainly in the Austroalpine crystalline rocks and the South Alpine Palaeozoic and Mesozoic cover-sediments in the Eastern Alps.

I graduated with a project on Rock Glaciers dynamics and hydrology, this phase left a special interest for quaternary deposits and modern glacial environments.

During my research on glaciers, studying old maps, photography and reports on the former extent of these features, I became interested in history, especially the development of geomorphologic and geological concepts by naturalists and geologists.

Living in one of the key area for the history of geology, I combine field trips with the historic research done in these regions, accompanied by historic maps and depictions. I discuss broadly also general geological concepts, especially in glaciology, seismology, volcanology, palaeontology and the relationship of society and geology.

Follow David Bressan on Twitter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Smaller objects would certainly destroy the ecosystem in the vicinity of the impact, similar to the effects of a volcanic eruption, but larger impacts could have a worldwide effect on life on the Earth.

We will here first consider the possible effects of an impact, and then discuss how impacts may have resulted in mass extinction of species on the Earth in the past.

Still, calculations can be made and scaled experiments can be conducted to estimate the effects. The general consensus is summarized here.

The Geologic Record of Mass Extinction It has long been known that extinction of large percentages families or species of organisms have occurred at specific times in the history of our planet. Among the mechanisms that have been suggested to have caused these mass extinctions have been large volcanic eruptions, changes in climatic conditions, changes in sea level, and, more recently, meteorite impacts.

While the meteorite impact theory of mass extinctions has become accepted by many scientists for particular extinction events, there is still considerable controversy among scientists. In this course we will accept the possibility that an impact with a large object could have caused at least some of the mass extinction events, as it would certainly seem possible given the effects that an impact could have, as discussed above.

Still, because of their are many other possibilities for the cause of mass extinctions, please read your book for the arguments against the impact theory. While there is still some debate among geologists and paloebiologists as to whether or not the extinctions that occurred at the K-T boundary were caused by the impact that formed Chicxulub Crater, it is clear that an impact did occur about 65 million years ago, and that it likely had effects that were global in scale.

What would happen if another such event occurred while we humans dominate the surface of the Earth, and what could we as humans do, if anything to prevent such a catastrophic disaster? Human Hazards It should be clear that even if an impact of a large space object did not cause the extinction of humans, the effects would cause a natural disaster of proportions never witnessed by the human race.

Here we first look at the chances that such an impact could occur, then look at how we can predict or provide warning of such an event, and finally discuss ways that we might be able to protect ourselves from such an event. Risk - It is estimated that in any given year the odds that you will die from an impact of an asteroid or comet are between 1 in 3, and 1 in , The table below shows the odds of dying in the U.

Although this seems like long odds, you have a about the of dying from other natural disasters likes floods and tornadoes. In fact the odds of dying from an impact event are much better than the odds of winning the Powerball lottery. Odds of Dying in the U. Data from Clark R. In March, an asteroid named FC passed within , km of the Earth, crossing the orbit of the Earth. It was not discovered until after it had passed through the orbit of the Earth.

Its size was estimated to be about 0. Such a body is expected to hit the Earth about once every million years or so, and would release energy equivalent to about 10, megatons of TNT, a little greater than the energy released in a nuclear war, and enough to cause nuclear winter event see graph above. Although , km seems like a long distance, it translates to a miss of the Earth by only a few hours at orbital velocities.

On March 19, , a 30 m diameter asteroid, named FH, passed within 26, miles 43, km of earth, just beyond the orbit of weather satellites. The object was small , and likely would have only caused a local effect if it had hit the earth's atmosphere, but it was discovered only 4 days before it passed. Although it was never a threat, the fact that it was discovered only a few days before was alarming. Furthermore, its size was originally estimated to be only m in diameter, as it passed, scientists realized that this was an underestimate.

Its size turned out to be about 1 km. Examples of questions on this material that could be asked on an exam. Natural Disasters. Meteorites, Impacts, and Mass Extinction. Meteorites On February 15, a meteor exploded in the sky over Chelyabinsk, southern Russia. Fireballs are very bright meteors.

Within recent history meteorites have even hit humans- - a small meteorite crashed through the roof of a garage in Illinois - A 5kg meteorite fell through the roof of a house in Alabama. Composition and Classification of Meteorites Meteorites can be classified generally into three types: Stones - Stony meteorites resemble rocks found on and within the Earth. Two types are recognized: Chondrites - Chondrites are the most common type of stony meteorite.

The collision of a cometary fragment is thought to have occurred in the Tunguska region of Siberia in The blast was about the size of a 15 megaton nuclear bomb.

It knocked down trees in an area about square miles, but did not leave a crater. Although still controversial, the general consensus among scientists is that a cometary fragment about 20 to 60 meters in diameter exploded in the Earth's atmosphere just above the Earth's surface.

A similar event if it happened over a large city, would be devastating. Other Sources While the asteroid belt seems like the most likely source of meteorites, some meteorites appear to have come from other places.

Some meteorites have chemical compositions similar to samples brought back from the moon. Others are thought to have originated on Mars. These types of meteorites could have been ejected from the Moon or Mars by collisions with other asteroids, or from Mars by volcanic eruptions.

Impact Events When a large object impacts the surface of the Earth, the rock at the site of the impact is deformed and some of it is ejected into the atmosphere to eventually fall back to the surface. An impact like the one that struck the Yucatan Peninsula, in Mexico about 65 million years ago, thought responsible for the extinction of the dinosaurs and numerous other species, created the Chicxulub Crater, km in diameter and released energy equivalent to about million megatons of TNT.

For comparison, the amount of energy needed to create a nuclear winter on the Earth as a result of nuclear war is about 8, megatons, and the energy equivalent of the world's nuclear arsenal is about 60, megatons. Impacts of large meteorites have never been observed by humans.

Much of our knowledge about what happens next must come from scaled experiments. As the solid object plows into the Earth, it will compress the rocks to form a depression and cause a jet of fragmented rock and dust to be expelled into the atmosphere. This material is called ejecta. The impact will send a shock wave into the rocks below, and the rocks will be crushed into small fragments to form a breccia.

Some of the ejecta will be hot enough to vaporize, and the heat generated by the impact could be high enough to actually melt the rock at the site of the impact. The shock wave entering the Earth will first move in as a compressional wave P-wave , but after passage of the compressional wave an expansion wave rarefaction wave will move back toward the surface.

This will cause the floor of the crater to be uplifted and may also cause the rock around the rim of the crater to bent upward. Faulting may also occur in the rocks around the crater, causing the crater to become enlarged, and have a concentric set of rings. The ejecta will eventually settle back to the Earth's surface forming an ejecta blanket that is thick near the crater rim and thins outward from the crater. Rocks below the crater that were not melted by the impact will be intensely fractured.

All of this would happen in a matter of 1 to 2 minutes. Meteorite Impacts and Mass Extinctions The impact of a space object with a size greater than about 1 km would be expected to be felt over the entire surface of the Earth.

Massive earthquake - up to Richter Magnitude 13, and numerous large magnitude aftershocks would result from the impact of a large object with the Earth.

The large quantities of dust put into the atmosphere would block incoming solar radiation. The dust could take months to settle back to the surface. Meanwhile, the Earth would be in a state of continual darkness, and temperatures would drop throughout the world, generating global winter like conditions. A similar effect has been postulated for the aftermath of a nuclear war termed a nuclear winter. Blockage of solar radiation would also diminish the ability of photosynthetic organisms, like plants, to photosynthesize.

Since photosynthetic organisms are the base of the food chain, this would seriously disrupt all ecosystems. Widespread wildfires ignited by radiation from the fireball as the object passed through the atmosphere would be generated.

Smoke from these fires would further block solar radiation to enhance the cooling effect and further disrupt photosynthesis. If the impact occurred in the oceans, a large steam cloud would be produced by the sudden evaporation of the seawater. This water vapor and CO 2 would remain in the atmosphere long after the dust settles. Both of these gases are greenhouse gases which scatter solar radiation and create a warming effect.

Thus, after the initial global cooling, the atmosphere would undergo global warming for many years after the impact. If the impact occurred in the oceans, giant tsunami would be generated. For a 10 km-diameter object the leading edge would hit the seafloor of the deep ocean basins before the top of the object had reached sea level.

The tsunami from such an impact is estimated to produce waves from 1 to 3 km high. These could easily flood the interior of continents. Large amounts of nitrogen oxides would result from combining Nitrogen and Oxygen in the atmosphere due to the shock produced by the impact. These nitrogen oxides would combine with water in the atmosphere to produce nitric acid which would fall back to the surface as acid rain, resulting in the acidification of surface waters. Major extinction events occurred at the end of the Tertiary Period, 1.

The maximum temperature difference due to the size distributions will be less than 1. The climate model calculation assumed spherical particles for all aerosol species, although soot particles generally consist of aggregated carbon spherules.

Numerical studies have shown that the aerosol optical properties e. These results suggest that climate changes caused by BC injection would be more greatly influenced by the amount of BC than the particle size and shape for the Chicxulub-scale asteroid impact. The average weight of hydrocarbons in sedimentary rocks is 0. The total thickness of sedimentary rocks in the present-day crust 43 was revised by removing thick Cenozoic sedimentary rocks.

Exceptionally thick Cenozoic sediments, such as those found in India due to the Himalayas, were removed and the white and olive areas were added in paleoceans located between the North and South American continents and between Asia and Africa—India at the end of the Cretaceous Fig. We also used the thickness ratio between the pre-Cenozoic and Cenozoic, or the thickness of the Cenozoic, in selected hydrocarbon-rich areas orange and magenta areas, Fig.

All values are approximate; estimated values are sufficient to obtain approximate areas and the probabilities of mass extinctions. There were no significant latitudinal differences in rates among organic carbon-rich areas Supplemental Table 3.

The volume of granite crust and mantle melt was higher at higher-impact angles, but granite and mantle rock are not a source of soot 33 , There are few hydrocarbons in the crust and mantle; therefore, we used only sedimentary rocks to estimate the amount of hydrocarbon.

The product of the burned weight and averaged hydrocarbon content provides the amount of hydrocarbon ejected by the impact of a 9-km asteroid on the Earth Table 1.

The amount of stratospheric soot generally depends on the soot emission factor, the fraction of soot injection to the stratosphere 0. The efficiency of soot formation from hydrocarbon may be also dependent on the chemical composition and the redox conditions in the bulk impact-induced vapor.

The overall surviving fraction in ejected soot that could be spread globally in the stratosphere is assumed to be 4. The surviving fraction of the Tg BC case was applied to all BC cases and the amounts of surviving stratospheric soot after the impact were estimated for every case Table 1.

The effect of stratospheric soot on the global mean surface air temperature anomaly was estimated using the K curve shown in Fig. The amount of sulfur from other sedimentary rocks is minor compared to that from evaporite-rich sedimentary rocks, so sulfur content was calculated as the average sulfur content in sedimentary rocks: ppm S Table 2.

The main source of sulfate aerosols in an oceanic crust impact is the mantle beneath the oceanic crust, because the volume of mantle materials ejected following an approximately 9-km asteroid impact is very large compared to oceanic crust and sedimentary rocks, calculated as having a km diameter of melting 44 , km thickness 44 , and — ppm sulfur content 50 , 51 Table 2.

These phenomena would occur near the impact location within a few days. We used two cases to estimate the amount of stratospheric sulfate SO 4 that survived after an impact. Following Ohno et al. Case 2 assumed that all sulfur was ejected as sulfate and that the surviving rate of sulfate was the same as that of soot. The amount of sulfate surviving in the stratosphere in case 2 was estimated to be the product of the weights of melted sulfur, the sulfur emission factor 0.

In case 1 we assumed the removal of all SO 4 produced from SO 3 from the atmosphere after the impact and the survival of a portion of soot. SO 3 and SO 2 are released from rocks evaporated or melted by an impact that covers a km-diameter area. Most silicate particles are sourced from silicate vapor from within the same impact area In contrast, soot is mainly formed in km-diameter area. The difference of source areas could cause that the sulfate particles were efficiently scavenged from the atmosphere by large falling silicate particles in their path; however, soot particles were less scavenged resulting in their survival.

We used published data 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 calculated by various global models in volcanic eruption studies to estimate possible temperature anomalies caused by sulfate aerosols. The calculation methods and treatments of the sulfate aerosols in the models e. The models can be roughly classified into three categories.

The models in the first category calculate climate effects explicitly by treating gaseous SO 2 concentration as volcanic emission, but do not treat aerosol size growth due to aerosol microphysics e. The models in the second category calculate climate effects by giving the aerosol optical depth, which is calculated by an another offline model that treats the effects of aerosol growth and sedimentation more realistically, resulting in smaller temperature anomalies that are likely due to shorter residence time 24 , 25 , 26 , 27 , The models in the third category calculate climate effects using sulfate loadings derived from the aerosol optical depth dataset, which yields temperature anomalies between those of the first and second categories but with results closer to those of the first category models 23 , 29 , We simply converted the initially given SO 2 mass in the stratosphere to the stratospheric SO 4 mass using molecular weights for some of the model results in Fig.

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