Journal Ranks Top 25 Unanswered Science Questions

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How Long Can Human Life Span Be Extended?

Life-span extension experiments in yeast, worms, and mice have convinced some scientists that humans may soon routinely coast beyond their hundredth birthdays. Other scientists say the human life span may be more limited. Whether possible or not, the prospect of an extended human life span "could have profound social effects," Jennifer Couzin notes in a related Science essay.

How Does Earth's Interior Work?

The revolutionary theory of plate tectonics—that the Earth's crust is broken up into fragments that jostle about our planet's surface—is only so deep. "There's another 6,300 kilometers [3,900 miles] of rock and iron beneath the tectonic plates whose churning constitute the inner workings of planetary heat engine," Richard A. Kerr writes.

As scientists probe the interior with ever more sophisticated instruments, researchers are finding that the Earth's engine is intriguingly complex beneath the hood. Advances in seismic imaging, the study of minerals, and computer modeling may provide clues to what makes Earth tick.

Are We Alone In the Universe?

The mathematical odds say no: There are hundreds of billions of stars in our own galaxy, the Milky Way, and hundreds of billions of galaxies in the universe. Close to home, scientists have already discovered 150 planets orbiting nearby stars.

In short, scientists say the universe is likely full of places where the conditions are ripe for intelligent life to evolve. "The really big question is when, if ever, we'll have the technological wherewithal to reach out and touch such intelligence," writes Richard A. Kerr.

How and Where Did Life on Earth Arise?

Recent experiments suggest that Earth's earliest life-forms could have been based on RNA—not the DNA and proteins essential to all free-living organisms today. (A single-strand molecule, RNA is similar to DNA, a double-stranded, helix-shaped molecule encoded with genetic information.)

As scientists gather around this origin model, other scientists are focusing on how the lifeless chemistry of a pre-biotic Earth gave rise to a RNA world. Other researchers debate where these primitive building blocks came together. Was it in deep-sea hydrothermal vents, tidal pools, oceans covered in glaciers? Or "perhaps Martian microbes were carried to Earth 4 billon years ago," Carl Zimmer speculates in Science.

Is an Effective HIV Vaccine Feasible?

Researchers identified the human immunodeficiency virus (HIV) as the cause of acquired immune deficiency syndrome (AIDS) two decades ago. Since then, the search for an effective vaccine to the deadly infection has received more funding than any other vaccine effort in history.

And the search, employing ever more innovative strategies, continues. Skeptics say no vaccine will ever be found. Whether successful or not, "the maps created by AIDS vaccine researchers currently exploring uncharted immunologic terrain could prove invaluable," writes Jon Cohen.

How Hot Will the Greenhouse World Be?

Scientists know that the world is warming and that humans are the cause behind most of this global climate change. Researchers are much less certain about how warm the Earth will become in response to the doubling of the greenhouse gas carbon dioxide that is expected in this century.

Modeling studies suggest Earth will warm by at least 2.7 degrees Fahrenheit (1.5 degrees Celsius) and maybe by as much as 19.8 degrees Fahrenheit (11 degrees Celsius). A better understanding of the climate system and more robust models will be needed to better forecast the temperature increase.

What Can Replace Cheap Oil? When?

The price of oil and the demand for energy are increasing. Oil supplies are dwindling, and the polar ice caps are melting. So the time is ripe for humans to transition from oil to a new source of energy. Alternative energy sources are available but need to be scaled up and made more cost efficient to replace oil. Advances in nanotechnology may be the answer. But will they come soon enough to avoid an energy crunch?

Will Malthus Continue to Be Wrong?

In 1798 English economist Thomas Malthus argued that human population growth will always stay in check, policed by war, famine, disease, and other blights. More than two centuries later, the global population has increased six-fold to more than 6 billion—without the large-scale collapses Malthus predicted. Demographers expect the global population will reach 10 billion by 2100. Can catastrophe continue to be avoided? Challenges will include a shift to more sustainable patterns of consumption and development, notes Erik Stokstad.

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