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Impact Events: Ecology Meets Cosmology

By Keith Cowing

February 23, 2001

Filed under General Story, National Aeronautics and Space Administration

impact event Using a novel form of linking events on Earth with objects in space, a research team as shown that a second large mass extinction of life on Earth was likely due to the impact of a large body millions of years ago. With this announcement, a clear picture is now available showing that the course of evolution on Earth is inextricably linked to extraterrestrial factors.

As has more or less been widely accepted in the past decade or so, the impact event 65 million years ago involving an asteroid marked the end of the Cretaceous period and the beginning of the Tertiary period (the so-called “KT event”). A massive extinction of a myriad of species followed the impact resulting in the end of the “age of Dinosaurs”. The Chicxulub crater on Mexico’s Yucatan Peninsula has been identified as being the probable site of the impact.

This was not a unique event. Earth has apparently been hit with some regularity (at least once every 100 million years or so) by a large impactor – each impact having global after effects. These periodic impacts, while certainly important to Earth’s history are mild compared to the early history of Earth when this planet pummeled with impacts on a much more frequent basis. One impact was large enough, (some scientists think ) to blast sufficient material out into space to form the Earth’s moon.

While things have settled down considerably as the solar system aged, the impacts have not stopped. The recent Shoemaker-Levy comet impact on Jupiter in 1995 drove home the point of how much effect such impacts can have on a planet – even on a planet as massive as Jupiter – and that such events can happen within the timeframe of human experience.

The Mother of all Impacts

As horrific as the KT impact event was upon Earth’s biota, it was mild compared to the event that marked the end of the Permian Period and the beginning of the Triassic Period (PT event) . A member of the research team, Luanne Becker from the University of Washington, referred to it as “the mother of all impact events.”

At least five such extinction events on Earth are now correlated with impact events – some (the KT and PT events) more reliably than others. These two are especially important since one (PT event) marks the end of one era and the dawn of what would become the ‘age of the dinosaurs’. The other, the KT event, signaled the end of the dinosaur’s reign and the advent of the evolutionary path that led to ecological dominance by mammals – and humans.

Based on the geological record, it has been suggested that PT event wiped out 90 percent of all marine species and 70 percent of land vertebrates. This mass extinction was caused not only by the immediate effects of the impact – but also by subsequent massive volcanism that covered large portions of the Earth’s surface.

According to the University of Washington: “many fossils below the PT boundary – such as trilobites, which once numbered more than 15,000 species – diminish sharply close to the boundary and are not found above it. There also is strong evidence suggesting the extinction happened very rapidly, in as few as 8,000 to 100,000 years, which the latest research supports.”

These impact events had a profound impact on Earth’s ecology – dramatically altering the types of life that were allowed to survive. Each impact event is unique in the types of life forms that disappeared and those that survived. There is a certain “selectivity” for each impact event. The types of organism that perished in the PT event was not the same as for the KT event. As such these impactors had different “kill mechanisms”.

There are two possibilities that would explain these differences. One is that the impactors were of different sizes and or compositions (comet Vs asteroid) and the effect they had was a function of their composition.

The second possibility has to do with what sort of planet they hit. Earth at the time of the KT event was very similar to Earth of today – multiple land masses spread out across the planet with a variety of oceans. During the PT event, however, Earth still had one large continent – Pangea – surrounded by a single world ocean. If the impactor hit in the midst of a vast ocean it would have very different effects than if it struck a landmass (as was the case for the KT impactor).

The PT event is accompanied in the geological record by large outpourings of lava. So much lava was released that had it been distributed evenly, it would have encircled Earth at depth of 30 feet. From this evidence, it would now appear that the Impact event itself triggered subsequent volcanism. As such – a 1-2 punch generated the PT mass extinctions: first the impact – then volcanoes.

Proving the Case: Buckyballs to the Rescue

As is the case with the KT event there is a very clear delineation (layer) in the geological record that marks this portion of Earth’s history – the Permian-Triassic boundary layer (PTB) . The date of this impact event has been placed at 250 million years ago. Until recently, according to Becker, scientists have not really been able to pinpoint the exact cause of this event. The possibility that this was also due to an impact event – one similar to KT event – was apparent to many.

Becker described a novel approach she and her colleagues used in tying in Earth-based evidence with extraterrestrial objects – the analysis of fullerenes or “buckyballs”. The name for the molecules (formally known as “buckminsterfullerenes” or “fullerenes”) comes from their complex geometric shapes that seem to have been lifted from the geodesic domes created by noted polymath Buckminster Fuller.

Fullerenes are a third natural form of elemental carbon – diamonds and graphite being forms common on Earth. Fullerenes, although created on Earth by humans, are only natural to the space environment – not that of Earth. Fullerenes are complex structures formed of carbon atoms – assemblages of 60 being one of the more common forms (others with more and less atoms are also known).

While naturally occurring fullerenes are not unknown on Earth, they are rather rare. They are much more abundant in space and have been found in the interstellar environment. Fullerenes are thought to form within clouds of material that surround – and are formed by – stars. Fullerenes are assembled atom by atom. At some point in their assembly as molecules become entrapped in the forming latticework. Once the entire structure has been formed these atoms can remain trapped within the fullerene molecule for very long periods of time. Eventually these fullerenes come to form pieces of solar systems – asteroids and meteorites (pieces of asteroids).

One sort of extraterrestrial object thought to be rich in fullerenes which have trapped helium atoms are carbonaceous chondrites. The asteroid Mathilda, encountered by the NEAR -Shoemaker spacecraft on its way to Eros, is an example of a large carbonaceous chondrite object. The Murcheson meteorite (which landed on Earth) is also a carbonaceous chondrite. When examined, this meteorite was found to have fullerenes. An object similar (perhaps a bit smaller) than Mathilda is thought to be what hit Earth 65 million years ago.

According to NASA “the telltale fullerenes containing helium and argon were extracted from sites where the Permian-Triassic boundary layer had been exposed in Japan, China and Hungary. The evidence was not as strong from the Hungary site, but the China and Japan samples bear strong evidence.

When the geological strata marking the PT event were analyzed for fullerenes they were found in abundance within that layer’s clays. Moreover, the fullerenes were found in the so called “dead zone” portion of these geological formations that resulted when Earth underwent cataclysmic change i.e. the point right after impact event itself and the extinction that followed.

Once characterized, the fullerenes were found to be a perfect match for those found at the KT impact site – as well as with those found in meteorites – and those observed in interstellar space by radio astronomers. The noble (unreactive) gases trapped inside these fullerenes have an unusual ratio of isotopes – in particular, helium . Earth’s inventory of helium is mostly the helium-4 isotope and with only a small amount of helium-3 whereas extraterrestrial helium – the kind found in these fullerenes – is mostly helium-3.

Since fullerenes do not form from biomass burning (the fires that would follow a large impact) their chance of being terrestrial in origin is slim. The molecules trapped within the fullerenes lattices would not result from entrapment within Earth’s atmosphere by other known mechanisms.

Comet or Asteroid?

According to Chris Chyba, “we now have evidence for an impact “trigger” – this raises some obvious questions”. One question, according to Chyba has to do with the sort of impactor involved. The KT event is thought to have been caused by a C-type (carbonaceous chondrite) asteroid. Asteroids contain Iridium, an element that is exceedingly uncommon on Earth. Locating an Iridium layer among deposits that mark the KT event was key in helping determine that an extraterrestrial body was involved. Examination of the PT boundary (where the fullerenes were located) shows ten times less Iridium than is present in the KT boundary. As such, Chyba and others feel that the PT impactor was probably not an asteroid.

Based on observations of cometary nuclei – most notably that of Comet Halley – it has been found that comets are ten times richer in organic compounds than carbonaceous chondrites. Comets also contain a substantial amount of ice. These organic abundances help explain what was found at the PT boundary. While it is though that the impactor was 6-12 km in diameter – smaller in size than the one which caused the KT impact – comets tend to hit planets at much higher velocities than asteroids – therefore imparting much more kinetic energy – and producing a larger blast.

Chyba and his colleagues were curious as to whether organic compounds could survive the hellish conditions that would accompany an impact – one whose energy output has been estimated 100 million megatons. Could the amino acids know to be in a comet survive? Chyba and his team modeled impact events on a computer and followed the temperature profiles within the impactor (and its debris) during and after impact. They found that a significant amount of amino acids would survive the impact. Moreover, given that fullerenes are substantially more robust molecules, it is all but certain they’d survive an impact in some abundance.

Impacts, Evolution, and the Origin of Intelligent Species

Chris Chyba suggested that the evolution of life on Earth is strongly tied to the cosmic environment. Noting that the periodicity of these large impactors is roughly 100 million years, Chyba suggested that such impact events turn the tables on a planet’s biosphere preventing any one ecosystem from becoming too static by reshuffling it on a periodic basis.

Similar processes – albeit on a physical and temporal smaller scale – were seen when a large forest fire devastated Yellowstone National Park and Mt. St. Helens erupted and devastated the surrounding terrain. In both cases, ecological cataclysm was followed by ecological renewal.

Chyba also saw implications in all of this for the evolution of intelligence. He hypothesized that 100 million years is a suitable timeframe wherein enough evolutionary experimentation could stumble upon a species with intelligence. He suggested that if a planet’s ecosystem had not managed to produce intelligence at the end of this period, an impact would clear the decks and the process could start all over again. If a species emerged that was not only intelligent enough – but capable of enough foresight – it could recognize these impact events for what they are and arrange to ameliorate or eliminate their effects. Again, if they don’t , an impactor will reset the evolutionary clock and probably erase them.

Assuming that other solar systems would have similar mechanisms at work – and this does seem to be the case since most extrasolar planetary systems have much in common with one another – and our own, then such a periodic adjustment of evolution might actually facilitate the development of intelligence in the universe.

The Intersection of Ecology and Cosmology

Up until the 1970’s prevailing ecological and evolutionary theory spoke of mechanisms driving the evolution of life forms as being products of changes on this planet. The sole exception (i.e. extraterrestrial) being the amount of sunlight received as the sun aged. In 1980 Nobel Laureate Louis Alvarez and his son Walter suggested that extraterrestrial forces – such as the impact of large asteroids or comets – could dramatically alter Earth’s environment . They proposed that these impacts would cause ecological calamities that would cause a dramatic change in the Earth’s biosphere.

At first their theory was scoffed at. Soon, mounting geological evidence, studies on the ecological impact of large scale thermonuclear war (so called “nuclear winter”) , and the growing realization that impact events are a regular – even common phenomenon brought this once heretical concept into mainstream acceptability. Similar experiences surrounded the acceptance of other, once heretical concepts such as continental drift , relativity – and – even the Copernican view of the universe.

We’ve also come to see that many of the organic compounds that comprise all living things were born amidst the death throes of stars only to be recollected eons later to form new stars, solar systems, planets – and life. Moreover there is a constant delivery mechanism onto planets for these materials over time in the form of cosmic dust, meteors, and the impact of comets and asteroids.

We have found life in so called “extreme environments” on Earth. Environments once though to be sterile are teeming with life. Environments similar to these are though to exist on a variety of worlds in our solar system – and probably, in other solar systems as well. Many of these environments are so isolated from the surface of our planet that the same impact events that can devastate life on the surface may have minimal effect upon life deep within the Earth. Indeed, such isolated pockets of life what may be what is called upon to help repopulate the Earth after it has received a particularly devastating blow to its biosphere.

Lastly, we’ve also uncovered evidence that rocks can be blasted off of one planet by large impact events and land on another . The ALH84001 meteorite from Mars (with possible Martian fossils inside) used the means to land on Earth. Moreover, it has now been shown that conditions inside these rocks are conducive to the transport of life.

What does this all mean?

The profound aspect of all of this is that life on Earth – not just its origin – but also its continued evolution – is deeply affected by extraterrestrial events. Indeed, planets may actually swap life between themselves. In the early history of the solar system, Mars is thought to have actually been more hospitable to the origin of life while Earth was still being bombarded – including the immense impact that may have formed our moon, sterilizing the entire surface of Earth in the process. It is not at all out of the realm of possibility that life could have been blasted from Mars and taken hold on an Earth recently devastated by a cataclysmic impact event. We could be Martians.

As such, to fully embrace the implications of repeated mass extinctions caused by asteroid impacts – and the resultant new life forms that appear in the wake of these events – one has to view life on Earth as truly being under the influence of extraterrestrial forces. Not the undefined mystical forces as the ancients once envisioned, but rather the rock-em sock’em tendency of the universe to blow things up and throw them around – again, and again, and again.

Life both arises from this process and is invigorated by it.

Related Links

° Impact Event at the Permian-Triassic Boundary: Evidence from Extraterrestrial Noble Gases in Fullerenes, Science [abstract] registration required. Subscription fee required for full access

“The Permian-Triassic boundary (PTB) event, which occurred about 251.4 million years ago, is marked by the most severe mass extinction in the geologic record. Recent studies of some PTB sites indicate that the extinctions occurred very abruptly, consistent with a catastrophic, possibly extraterrestrial, cause. Fullerenes (C60 to C200) from sediments at the PTB contain trapped helium and argon with isotope ratios similar to the planetary component of carbonaceous chondrites. These data imply that an impact event (asteroidal or cometary) accompanied the extinction, as was the case for the Cretaceous-Tertiary extinction event about 65 million years ago.”

° Asteroid or Comet Triggered Largest Mass Extinction in Earth’s History, Foreshadowing Fate of Dinosaurs, NASA

° Asteroid or comet triggered death of most species 250 million years ago, University of Washington

° Stowaways From Space Provide Link Between Impact, Biggest Extinction in Earth History, University of Rochester

° NEO News (02/22/01) Permian impact?

Background Information

° Buckyballs Found to Contain Extraterrestrial Gases, SpaceRef

° Researchers Discover Extraterrestrial Gases in Buckyballs, NASA ARC

° Researchers Discover Extraterrestrial Gases in Buckyballs, University of Hawaii press release

° Astrochemistry, SpaceRef Directory

° Astrochemistry Lab, NASA Ames Research Center

° Department of Earth and Environmental Sciences, University of Rochester

° Cosmochemistry Program, University of Hawaii