Wie man ein Massensterben überlebt

Werfen Sie einen Blick aus Ihrem Fenster. Bäume wiegen sich träge im Wind. Vögel gleiten mühelos durch die Luft. Ein genauerer Blick zeigt Ameisen, die pflichtbewusst den Bürgersteig entlang marschieren. Das Leben ist überall um dich herum. Stellen Sie sich jetzt dieselbe Szene vor, aber mit drei Vierteln dieser Pflanzen und Tiere, die tot sind. Deprimierend, oder? Nun, es stellt sich heraus, dass diese Realität möglicherweise nicht so weit hergeholt ist, wie Sie vielleicht denken. Es ist schon einmal passiert und es kann wieder passieren. Die Frage ist: Bist du bereit?

Das Aussterben selbst ist keine große Sache. Es geschieht seit Millionen von Jahren in einem natürlichen Tempo, das Wissenschaftler Hintergrundaussterberate nennen . Aber wenn eine Vielzahl von Pflanzen und Tieren aus der ganzen Welt viel schneller als die Hintergrundrate auszusterben beginnt, IST das eine große Sache. Wissenschaftler bezeichnen solche Ereignisse als Massensterben .

In den letzten 500 Millionen Jahren haben fünf Massensterben (zusammen als „The Big Five“ bekannt) zur Ausrottung von mehr als 75 Prozent der damals lebenden Arten geführt, typischerweise in einem Zeitraum von weniger als 2 Millionen Jahren [Quelle: Newitz ]. Grundsätzlich haben Naturphänomene wie Meteoriteneinschläge und atmosphärische Veränderungen das Klima der Erde viel schneller verändert, als sich die meisten Pflanzen und Tiere anpassen könnten. Dasjenige, mit dem Sie wahrscheinlich am besten vertraut sind, ist das Kreideereignis, das vor etwa 66 Millionen Jahren stattfand und für das Absterben der Dinosaurier verantwortlich war [Quelle: Natural History Museum of London ]. Jetzt glauben Wissenschaftler, dass wir uns in den frühen Wehen eines sechsten großen Massensterbens befinden, das größtenteils von uns selbst verursacht wurde.

Okay, ein Haufen Pflanzen und Tiere sterben ab. Warum sollten wir uns darum kümmern? Nun, Pflanzen und Tiere tun eine Menge Dinge für uns, von der Reinigung unserer Luft und unseres Wassers bis hin zur Bestäubung unserer Pflanzen. Angesichts unserer komplexen Beziehungen zu anderen Lebewesen ist sich niemand wirklich sicher, was bei einem erheblichen Verlust der Artenvielfalt oder der Vielfalt des Lebens auf der Erde passieren könnte. Aber es ist wahrscheinlich bestenfalls unangenehm und schlimmstenfalls katastrophal.

Werden wir überleben? Vielleicht. Vielleicht können wir einige Hinweise von Tieren bekommen, die vergangene Massensterben überlebt haben. Vielleicht können wir einen Ausweg aus allen Problemen finden, auf die wir stoßen. Es könnte sogar möglich sein, das Ganze abzuwenden, bevor es schlimmer wird. Es hängt alles davon ab, wie sich die Dinge entwickeln.

1. Vergangene Massensterben
2. Anzeichen für ein zukünftiges Massensterben
3. Wie Tiere Massensterben überlebt haben
4. Wie Menschen ein Massensterben überleben können
5. Wie man ein Massensterben verhindert

Um ein besseres Gefühl dafür zu bekommen, wie ein Massensterben aussehen könnte (und wie wir es überleben könnten), lassen Sie uns diejenigen untersuchen, die bereits stattgefunden haben. Ich hoffe, Sie setzen sich hin, denn das ist ein ziemlich intensives Zeug.

Wie wir bereits erwähnt haben, hatten wir bis zu diesem Zeitpunkt fünf große Massensterben [Quelle: Barnosky et al. ]:

Das ist viel Tod. Aber was könnte eine solche Massenverwüstung verursachen? Die Ursachen für diese Ereignisse lesen sich wie der gruseligste Apokalypse - Roman, den man sich vorstellen kann. Vulkanausbrüche, Meteoriteneinschläge, globale Temperaturschwankungen und Veränderungen in der Zusammensetzung der Atmosphäre und der Ozeane sind alle für das eine oder andere Massensterben verantwortlich. Noch beängstigender: Während die meisten dieser Absterben über Tausende oder sogar Millionen von Jahren stattfanden, hat das Kreideereignis möglicherweise innerhalb weniger Monate seine Verwüstung angerichtet.

Nehmen Sie das Perm-Ereignis, das krankhaft als „Das große Sterben“ bezeichnet wird. Einer Erklärung zufolge begann dieses Aussterben vor etwa 252 Millionen Jahren, als die Erde eine riesige Landmasse hatte, die als Pangaea bekannt war [Quelle: Natural History Museum of London ]. Die globalen Temperaturen waren höher als je zuvor, was die innere Wüste des Kontinents extrem heiß und trocken machte. Das Leben hielt kaum noch an.

Dann begann einer der größten Vulkanausbrüche der Geschichte, der riesige Landstriche mit Lava bedeckte und riesige Wolken aus Asche und giftigen Gasen in die Luft spuckte. Nach einer kurzen Periode von saurem Regen und globaler Abkühlung begann sich der gesamte Planet stark zu erwärmen. Kohlendioxid aus den Vulkanen füllte die Atmosphäre und erzeugte einen Treibhauseffekt. Nach 160.000 bis 2,8 Millionen Jahren der Verwüstung (eine lange Zeit nach unseren Maßstäben, aber nicht nach denen der Erde) waren 96 Prozent aller Arten ausgestorben [Quelle: Barnosky et al. , Natural History Museum of London ].

Offensichtlich wird das Überleben eines Massensterbens kein Kinderspiel sein.

To the regular Joe on the street, it doesn't seem like we're in the midst of a mass extinction. Even experts admit that only 1 or 2 percent of all species have gone extinct in the past 200 years [source: Pappas]. That's a long way from the 75 percent needed to join the mass-extinction club. So what's gotten scientists worked up?

If you'll recall from earlier, a mass extinction can occur when plants and animals start dying off a lot faster than the normal, or background, rate. So a great way to see whether we're headed toward such an event is by looking at the current extinction rate versus the background extinction rate. And sure enough, a number of studies have done just that.

One of the more pessimistic findings estimates that the background rate of extinction for all species is 0.1 extinctions per million species per year (E/MSY), while the current rate is more like 100 E/MSY. That would mean we're losing species 1,000 times faster than normal [source: Orenstein]. Yikes! A more optimistic study, which looked only at mammals, pegged the background rate of extinction at 1.8 E/MSY, and the current rate at 50 to 75 E/MSY. But even in that supposedly rosy scenario, the current rate is at least 27 times too high [source: Simons].

What, then, is causing all of this? One problem is habitat loss. As the global population expands, more land is being cleared for farming, leaving less room for the creatures that lived there before. Another big issue is that many species are being driven to near extinction for short-term economic gain (think poaching and overfishing).

The explanation receiving the most attention, however, is human-caused climate change: When we burn fossil fuels, carbon dioxide is released into the atmosphere where it traps heat from the sun and causes the planet to warm. Some plants and animals just can't adapt fast enough to the changing environment and are dying off as a result [source: Barnosky].

If we are indeed experiencing a mass extinction, that doesn't mean we're goners. Plenty of creatures have survived before.

Science Speak

You probably noticed that scientists measure extinction in terms of extinctions per million species per year (E/MSY). So what does that mean exactly? Let's say, hypothetically, the background rate of extinction is 1 E/MSY and there are 1 million species on Earth. That means you would expect one species to die out every year. The higher the E/MSY number, the more species that are going extinct.

Survivors of mass extinctions are in a pretty elite club. And unlike today's doomsayers, they didn't have guns, bomb shelters or food storage to help them out. What is it they were doing right?

To answer this question, let's look at Lystrosaurus, one of the greatest survivors of all time. This creature was a part of the lucky group that survived the Permian event, which, if you recall, killed 96 percent of all species on Earth. Especially surprising is that Lystrosaurus wasn't a tiny algae or insect: It was a mammal-like reptile about the size of a pig, basically the only animal of its kind to dodge extinction.

Lystrosaurus had a number of things going for it. One was that it was a burrower. As any survivalist worth his or her salt can tell you, underground is a pretty good place to be when something bad happens. Plus, breathing underground was good form during the Permian event, when low oxygen levels and dusty airborne contaminants became the norm.

Another tool in Lystrosaurus's survival kit was its ability to move and spread out over great distances. When things got bad, the creature was evidently capable of waddling to safer climes, eventually inhabiting areas all over Earth's super-continent, Pangea. And how was it able to adapt to so many places? A big reason is that it was a generalist species, meaning, among other things, that it wasn't a picky eater. Although it ate only plants, its beak-like mouth was equally effective at chomping down rough vegetation and digging for roots.

Other species have survived mass extinctions by virtue of their small size. Obviously, little creatures don't need as much food as their larger counterparts (think mice versus elephants). They also tend to reproduce more, which gives them a larger, more genetically varied population that can adapt more quickly and effectively to change.

In a lot of ways, mass extinction survival just came down to luck. Certain species had certain traits that helped them endure whatever awful things befell the Earth. So is the survival of the human race really just a game of chance?

When most people think about survival, they think about things like personal protection, emergency shelters and food preservation. Sure, that stuff might help in the short term, but this is a mass extinction we're talking about! You can't dehydrate enough food to last 2 million years! Instead, it's going to take some serious, long-term changes in human behavior and technology to survive something like that.

While humans have never had to survive a Big-Five-style extinction, we certainly have displayed some qualities needed to do so. Remember Lystrosaurus, which was able to spread across the globe and adapt to various climates and food sources? We did that, too — 60,000 to 130,000 years ago [sources: National Geographic, Rodgers].

Members of the Homo sapiens species departed their African homeland, eventually inhabiting almost every continent [source: National Geographic]. Guesses about what spurred this migration range from massive drought to a volcanic eruption [sources: Gugliotta, Newitz]. Regardless of what happened, this example shows that even if hardship forces us to pack up and move, we can still survive and even flourish.

Of course, our greatest advantage over all previous species is — you guessed it — technology. What if the climate begins killing our crops? Perhaps we can genetically engineer our food to be hardier. What if a large asteroid is on a collision course with Earth? Maybe we can land a spacecraft on it and push it away. Some of the most fascinating extinction-dodging research is in geoengineering, a field in which scientists study ways to control our climate with technology. Imagine floating arrays of mirrors that deflect sunlight to cool the planet, or artificial trees that pull carbon dioxide out of the air and inject it underground. As crazy as it sounds, these and other solutions are possible, and they might even work.

But what if they don't? There's only one other option, really, and that's to go live somewhere else. Not another city, country or continent, but another world entirely. Scientists have long dreamed of building structures designed to mimic Earth's conditions on other planets, and some have even suggested that we could geoengineer the whole planet to function like our own.

But before we wander too far into sci-fi movie territory, let's have a reality check. Do we really want to rely on untested technology to save us? Perhaps, as the next section suggests, we should try to prevent this sixth big mass extinction from getting even worse.

Blame the Cyanobacteria

If human-caused climate change ultimately brings on the sixth big mass extinction , we wouldn't be the first creatures to cause such an event. About 2.5 billion years ago, a microbe called cyanobacteria became the first organism to photosynthesize, or use sunlight and water to create energy. Through this process they also released a tremendous amount of oxygen, which ultimately killed off just about everything that couldn't breathe it. What do we humans have that cyanobacteria didn't? The presence of mind to head off the next mass extinction [source: Newitz].

All that geoengineering stuff sounds pretty amazing, but it raises some real concerns. For one, there will almost certainly be unintended consequences from large-scale climate experiments. But perhaps just as troubling is that we, as a society, might start counting on scientists to bail us out when we might be better served taking action on our own. After all, if all of us are nudging the Earth toward a mass extinction, shouldn't we all be part of the solution?

If we're going to try to stave off a mass extinction, the first thing we need to do is address human-caused climate change . Some scientists think we may have already passed the point of no return, but a 2014 report by the United Nations' Environment Program and the World Resources Institute suggests there is still a glimmer of hope. In order to hold global warming under 3.6 degrees Fahrenheit (2 degrees Celsius), the standard they set to avoid dangerous climate change, we need to reduce greenhouse gas emissions by a daunting 50 percent by 2050 [source: Sheridan].

How? For starters, combine trips in your car. Buy more efficient cars. Adjust your thermostat down in the winter and up in the summer. Bike to work. Recycle. These may seem like small changes, but if everyone pitched in, the effect could be huge [source: Barnosky]. Take something as simple as a light bulb: If every American replaced one incandescent bulb with an Energy Star -rated one, the reduction in greenhouse gas emissions would be equivalent to taking 800,000 cars off the road [source: EPA].

Another extinction-maker is habitat loss. Now I like a juicy hamburger as much as the next carnivore, but reducing meat consumption would help out in a big way. Crops provide more calories per acre than livestock , so you can feed more people with less land. That's because you need land to grow livestock feed in addition to the land needed to pasture the animals [source: Oremus].

Finally, there's the problem of poaching and overfishing. Don't buy products that come from endangered species (like ivory) and try to purchase seafood from sustainable fisheries. For a little guidance, hop over to the IUCN Red List to search for endangered species and the Monterrey Bay Aquarium Seafood Watch to find seafood recommendations.

In the end, no one is sure how much we can do at this point. We've already changed our climate so much that these steps might only delay the inevitable. But to state the obvious: We're either going to have to try to prevent a mass extinction or cope with it. Here's to hoping we can make Lystrosaurus proud.

Author's Note: How to Survive a Mass Extinction

I can't think of a heavier topic than mass extinction. Pondering the death of 75 percent of all species on Earth, possibly including your own, is a harrowing task for any author with a healthy sense of self-preservation. But among all the bad news, I think there are some positive things to take away from this article. Humans have always shown an incredible capacity to persevere when disaster strikes. And what's more, there are a lot of really smart people who are already thinking of ways to ensure our survival. Perhaps the alien race who discovers the smoking rubble that was planet Earth will read this sentence and laugh, but I don't think we'll go down without a fight.

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