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Showing posts with label earth. Show all posts
Showing posts with label earth. Show all posts

June 15, 2011

The Earth after humans


In a review of studies documenting how will the Earth after humans have collapsed all ecological systems. It talks about the consequences and possible recovery of the planet, no longer human.

Nobel laureate Paul Crutzen proposed ten years ago the word Anthropocene to give birth to a powerful idea: human activity is now affecting Earth so deeply that we are entering a new geological era.

You might accept Anthropocene as geological period, but still end up being the shortest of all and the last. It is not difficult to imagine a time to finish just a few hundred years it has started, in an orgy of global warming and overconsumption.

Suppose that this latter occurs. The human footprint on the natural world, ever expanding in the last two or three centuries, leading to ecological collapse and mass extinction. Without fossil fuels to support agriculture, humanity would be in difficulties.

A lot of things have to die, and a lot of these things will be humans, said Tony Barnosky, a paleontologist at the University of Berkeley. In the most pessimistic scenarios society would collapse, leaving behind a few thousand people who lead a precarious existence in a new Stone Age.

If our species survives or not is difficult to predict, but what is the fate of Earth itself? It is often said that when it comes to saving the planet really are talking about saving ourselves, because the planet will be fine without us.

But would it be so, or the cataclysm at the end of the Anthropocene so severely damage the world would become a wasteland and barren? The only way to tell is to look at the history of our planet. Neither climate change and mass extinctions are unique to the current time. The Earth has gone through them before. So what can we expect this time?

Consider the greenhouse warming. The main concern of climatologists is that global warming push the Earth's climate system beyond two peaks that would make things dramatically worse.

The first would be the emission of carbon dioxide from the permafrost. As the Arctic becomes warmer, the decomposition of the peat will issue 3 billion tons of carbon (perhaps exceeding 3 billion tonnes that human beings could issue to consume all the fossil fuel conceivable).

The second is the emission of methane stored in clathrates in ocean sediments. As the ocean warms, methane (a potent greenhouse gas) into the atmosphere and will contribute even more to global warming, thereby accelerating a vicious cycle.

If we put all the fossil fuels in the atmosphere, temperatures would reach the point where both stocks of carbon would be released, says oceanographer David Archer of the University of Chicago. Nobody knows how warming would be catastrophic.

This is the reason why climate scientists are looking with increasing interest at the time 55 million years ago called the Paleocene-Eocene Thermal Maximum, when temperatures rose 9 degrees Celsius in a few thousand years (approximately the current rate climate prediction).

It is the most recent time in which there was a rapid warming, says Peter Wilf, a paleobotanist Esatdo University of Pennsylvania. And precisely because it was so recent, there are still rocks that have record of the event.

By the measures of ocean sediments deposited in the thermal maximum, geochemist James Zachos of the University of California at Santa Cruz, has found that warming coincided with a large increase in levels of atmospheric carbon dioxide.

Between 5 and 9 billion tons of carbon entered the atmosphere at no more than 20,000 years (Nature, vol 432, p 495). Where did that amount of carbon? Volcanic activity can not account for the increase of carbon dioxide, says Zachos.

Instead, he blames the breakdown of peat, which could have resulted not from the melting of permafrost (it was too hot to have permafrost at that time), but a change that made the world more dry. The fossil record of plants at the time testified that episode of drought.

Spike of carbon:

If Zachos and his collaborators are right, then 55 million years ago the earth went through a crisis similar to what is happening now: a sudden surge of carbon dioxide, followed by an uncontrolled release even more greenhouse gases emissions.

What happened next can let us take a look at what is expected to occur if the present crisis hit with full force. Geochemists have long known that when a pulse of carbon dioxide enters the air, most of it dissolves in the surface layers of ocean before gradually disperse into deeper water.

In a few centuries it reaches equilibrium with about 85% of carbon dioxide dissolved in the oceans and 15% in the atmosphere. This carbon dioxide persists tens or hundreds of thousands of years (which Archer believes he will be the "long tail" of the Anthropocene).

Until recently, however, climate models were a bit confused about what it would be this trail. Until studies of the past we had some degree of uncertainty in the models? Zachos said. Their studies are beginning to clarify these uncertainties.

Carbonate rocks of the ocean floor show that the oceans were too acid for the recovery of emissions (Science, vol 308, p 1611).

But this extreme acidification lasted only between 10,000 and 20,000 years, a blink in the eye of standard geological time, and the oceans returned to near normal conditions after the next 150,000 years. Even the storage of peat and methane hydrates may have been regenerated in 2 million years, Zachos said, because at that time the world suffered another crisis of carbon, which they had to be involved peat or clathrates.

This suggests that the long wake of the Anthropocene is unlikely to last more than 2 million years (even a short geological standards). However, the actual carbon recovery differs from the late Paleocene an important factor: our planet is now colder than at the time, so the warming will have more profound effects

. During the late Paleocene the world was warm and ice free. Now we have a bright white polar ice caps reflect sunlight into space. The melting of this ice will result in dark areas of rock and soil to absorb solar energy.

And the merger will raise the sea level, which will cause the permafrost to thaw more quickly, pushing the warming even further. This extra hit Earth could get out of this cycle of glacial and interglacial periods and bring it back to a former state warmer.

The Earth was free of ice for millions of years:

The present ice ages have occurred only during the last 35 million years, so we could get us out of ourselves there, said Pieter Tans, an atmospheric scientist at NOAA in Boulder (Colorado).

Even so, the new world free of ice would return to a state vaguely familiar. In this reading of the evidence, including the most dramatic climatic catastrophe would be unlikely to push the physical limits of the Earth into uncharted territory. Not so fast, says James Hansen, director of the Goddard Institute for Space Studies at NASA.

He argues that past episodes are a good guide to what's going to happen in the future for the simple reason that the sun is a little brighter now than then.

Add this mixture to release methane and carbon dioxide could give rise to a catastrophic and unstoppable global warming called "syndrome of Venus" would cause the boiling of the oceans and Earth lead to a similar fate to that of its neighbor roasted .

What would happen to life on Earth?

If Hansen is correct, the Earth would be directed toward sterilization. But if the scenario is more benign would be a different story. Biologists say it may already be at the beginning of an extinction event that could potentially result in one of the largest mass extinction events, one that would alter the course of evolution.

Strangely, the Thermal Maximum climate changes did not result in great loss of biodiversity. Nobody pointed out to the edge as the Paleocene-Eocene boundary of a large animal species.

Not even a minor, said Scott Wing, a paleobotanist the Smithsonian in Washington DC. Instead, the fossil record simply shows how species migrated, following their preferred climate throughout the globe. Today, of course, that's not possible due to the presence of roads, cities and farmlands that have broken many natural habitats.

Polar and alpine species will find their habitats will have vanished completely, not to mention the other ways in which people put endangered species.

We are in a "storm total" in terms of biodiversity concerns, says David Jablonski, a paleontologist at the University of Chicago. Not only are we overfishing and overhunting.

Not only are we changing the chemistry of the atmosphere and ocean acidification. Not only are we removing large animals. We are doing this simultaneously. Despite this, Jablonski believes that humans are not capable of causing a mass extinction comparable to that of the Permian, 251 million years ago, when an estimated 96% disappeared marine species and 70% of the land.

If the Anthropocene mass extinction possibly equal in magnitude to the Permian or less than something that is still evolving on the table deck.

Once again, the past gives us an idea of ​​what to expect. The fossil record tells us that each species behaves differently because each has its own unique causes.

However, there is one common factor: the species most at risk are those with narrow geographical range. Studies Jablonski has made snails show that species with planktonic larvae (which are widely dispersed) resist better than other species with more restricted distribution (Science, vol 279, p 1327).

World of cockroaches:

Add to that massive disruption of habitat, said Jablonski, the recovery of life after the end of the Anthropocene. Small-bodied animals, high rates of reproduction and the ability to exploit disturbed habitats will demonstrate all the advantages.

It is a kind of world with rats and cockroaches herbs, says Jablonski. The wave of species extinction sweep in a fairly predictable. First likely lose species already in danger, then come the following, Barnosky said.

Eventually reach the species that we believe are not in danger at present, for example, many African herbivores today seem to have healthy populations. However, predictions about the fate of a particular species are nearly impossible, and that luck plays a role.

The survivors will probably be more or less a random selection of herbaceous plants and opportunistic animals, notes Doug Erwin of the Smithsonian. If the Anthropocene ends with a mass extinction, the fossil record tells us much about the recovery. If the news is good or bad depends on your perspective. Recovery is quick from the geological point of view, but from the human point of view is incredibly slow.

We're talking millions of years, says Jablonski. Immediately after a mass extinction, the evidence from the fossil record suggest that ecosystems reach a state of shock for several million years.

For many millions of years after the Permian extinction, for example, the marine environment of the world was dominated by the same 25 or 30 species.

It's boring, "says Erwin. Something similar happened on land after the Cretaceous extinction. The North American plant fossils testify before the event that ecosystems flourish, with a variety of insects feeding on a wide variety of plants.

After sunset, however, both the diversity of plants as insect declined dramatically, with some feeding methods that disappeared almost completely. After that, confusion reigns for 10 million years.

According to the fossils were various combinations: one with few insects and plants, some with many insects but few plants, others with many plants and few insects, everything except the settings that ecologists call "normal" (Science, vol 313, p 1112).

At no time can we have what is called a healthy ecosystem with a diversity of insects feeding on a wide range of plants says Wilf.

Diversity remained low, with few new species to evolve. Just try to resist, says Erwin. A study of marine fossil diversity supports the same.

Nearly a decade ago, James Kirchner, University of Berkeley, and Anne Weil of Duke University (North Carolina), took a database of all marine fossils and used to determine how closely the peaks were speciation of the peaks of extinction (Nature, vol 404, p 177).

As everyone thought that when there is an extinction once recovery starts immediately, said Kirchner, now at the Swiss Federal Research Institute for Forest Snow and Landscape Birmensdorf. Instead they found that the peak of speciation was 10 million years after the extinction.

We almost fell off our chairs, he says. In fact, during the first billion years after the extinction of speciation rate actually dropped.

This suggests something like a wound biosphere. Extinction events not only remove organisms in the ecosystem, leaving plenty of opportunities to diversify into new species.

Instead, what we think happens is that the niches themselves collapse, so no new bodies have emerged to fill them. Niches cease to exist by themselves, says Kirchner.

Eventually, however, the evolution ends up winning, and after a few tens of millions of years recovering biodiversity. Sometimes, as after the Ordovician extinction of 440 million years ago, the new scheme is much like before.

But more often emerges a new mundo.No restore previous chessboard, but are redesigning a new game, says Erwin. In the Permian, the oceans were dominated by filter feeders, hows the brachiopods and sea lilies, which lived all his life anchored to the bottom. The predators were scarce. That all changed after extinction, resulting Lujar a more rich and dynamic ecosystem.

From my point of view of the Permian extinction was the best thing that could happen to life on Earth, says Erwin. Then, in a perverse way, in the end the lesson is positive. Even if over-crowded and to return to the Stone Age, the Earth will probably survive. Life will continue.

When the wake of the Anthropocene is gone, and what little there was left of humanity is gone, a new geological era appear. A shame that no one there to give it a name.

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