A question often asked by those involved in the Search for Extraterrestrial Intelligence (SETI) is, "How long can advanced civilizations last?" The search for intelligent aliens is much less likely to succeed if cultures inevitably destroy themselves when they reach a certain level of technology. So the Drake Equation, which tries to estimate the possible number of intelligent alien civilizations in the galaxy, includes a factor for longevity.

Cultures on Earth rise and fall for various reasons; the Fall of Rome is the most famous, but scholars are still debating exactly why it happened. With modern technological threats like nuclear weapons, climate change caused by burning fossil fuels, and genetically-engineered viruses now at hand, our current culture's downfall might seem inevitable to students of history.

Yet astronomers tend to be more optimistic, and dream of a far-future society where we re-engineer the solar system or travel to the distant stars.

The longevity of our civilization was the topic of a symposium recently held in Washington DC. The symposium was organized and led by the holder of the NASA/ Library of Congress Astrobiology chair David Grinspoon, in an ornate room that would not have been out of place in ancient Pompeii -- before that city was destroyed by an enormous volcanic eruption.

The complexity of answering the question of our longevity was evidenced by the far-ranging discussion that ensued among the panelists and the audience. Beyond science and technology, they discussed the current state of economics and politics, the fate of the environment, and even McDonald's plastic cups, which were designed to be used for 20 minutes but might outlive us all.

Never before has human civilization so greatly impacted our planet. Our sheer numbers -- over 7 billion and growing -- are a strain on Earth's natural resources, and add to the increasing pollution of the ecosystem. Also, our science and technology have grown so advanced and wide-spread that we can fundamentally alter the natural functioning of our planet, whether we intend to or not.

This time in human history has been labeled "The Anthropocene," and Grinspoon is currently writing a book on the topic.

"The Anthropocene Era is a time where humans are influencing the functioning of Earth," said Grinspoon. "But is the Anthropocene merely another geological era, or are we on the cusp of a transition into a profoundly new stage of Earth's existence?"

The natural world and our impact on it was one of the main topics debated during this symposium. Odile Madden, a materials scientist and engineer at the Smithsonian Museum, said that we often consider Nature as some pristine realm separated from human influence, and we pollute that natural world by our mere presence (as well as our plastic products, like those McDonald's cups). She said this is a sterile attitude, preventing us from ever being able to truly interact with Nature.

While our modern experience is to be disconnected from Nature, Rick Potts, paleoanthropologist and director of the Smithsonian's Human Origins Program, said the Native American way of thinking is that Nature and human culture are "one."

This attitude may have helped humans survive and adapt to changes in the past, for the one constant about Earth is that it is a system always in flux. The panelists agreed that keeping the world "as-is" was not possible, or even desirable.

But since we have such an impact on our planet, often altering the world merely by living in it, we should take care about the changes we impose. As one panelist noted, we may create so many new species through biotechnology that we generate a burst of new lifeforms like in the Cambrian Explosion... but should we?

So then comes the challenge: how do we not impose our view of how Nature "should be" in our attempts to preserve it? The discussion amongst the panelist revealed there is not yet a global "we," and the different cultures around the world make it difficult to make decisions about what's good for us and the planet. Potts noted that environmentalists in North America promote wilderness, but those in Germany, India and elsewhere have different priorities.

"What do we mean by 'saving the world'?" asked Grinspoon. "We have to better define our values before we can answer that."

Looking beyond our world, science fiction writer Kim Stanley Robinson stated, "Humans shouldn't go to Mars to save ourselves, but because it is a project of great interest and beauty." At the same time, we should preserve our own planet because, in his view, it is fundamental to our longevity -- we simply cannot live without it. "We are bubbles of Earth," he said.

Robinson also was very concerned about the state of current world affairs and what that meant for our future. "Our economic systems are unjust and inefficient," he said. "We must think of ways to improve them if we are to survive. The one-percent profit from the complexity of the financial system; confusion is a political act. So is simplicity."

"We can't just muddle along anymore," he added. "It's either utopia or catastrophe."

Artificial intelligence was discussed as a possible route toward a new way of being. SETI astronomer Seth Shostak predicted we will soon develop a machine with the functionality of our brain, even if we don't quite understand how it works. Many sci-fi movies look to the development of A.I. as our downfall, when the machines achieve consciousness and destroy the human race.

But futurist Ray Kurzweil has suggested that, instead, when "the singularity" happens and we are able to merge with our newly intelligent machines, a glorious new phase of existence may begin.

But Robinson said he doubts the singularity will happen, or even that we will download ourselves into machines, because we just don't understand consciousness. "Ray Kurzweil is telling a science fiction story", he said. "The singularity is not based on an understanding of the brain."

Of all the threats to our survival, Grinspoon said that in his view, global warming is the most imminent. But even without that looming over us, Earth will always be presenting us with new challenges to overcome.

Our planet is ever-changing, either due to the activities of man or through other means, and there will come a point when we can no longer adapt to those changes. So geo-engineering and other advanced technology, as scary and potentially threatening to our longevity as they sometimes seem to be, may actually be the key to helping us survive long-term.

Summing up, Grinspoon said, "We need technology if we want to live well with 9 billion people on the planet. We can't go backwards."

The symposium participants were David Grinspoon, planetary scientist and 2013 Baruch S. Blumberg NASA/Library of Congress Chair in Astrobiology, journalist David Biello, atmospheric scientist Ken Caldeira, astronomer, historian, and next LOC Astrobiology chair Steven Dick, planetary climatologist Jacob Haqq-Misra, professor of English Ursula Heise, materials scientist and engineer for the Smithsonian Odile Madden, paleoanthropologist and director of the Smithsonian's Human Origins Program Rick Potts, science and environmental writer Andrew Revkin, science fiction author Kim Stanley Robinson, and SETI astronomer Seth Shostak.