Aliens Could Detect Life on Earth. Here's How.

From gases in the atmosphere to satellites in space, Earth is sending plenty of signals that something here is alive.

ONE STRANGE ROCK, a global event series, premieres tonight, March 26, at 10/9C on National Geographic.

As the universe's only known harbor for life, Earth is arguably one strange rock. But light-years from our solar system, other intelligent beings on a similar planetary oasis might be gazing in our direction and seeing us as a sign that they're not alone in the universe.

To date, astronomers have confirmed the existence of nearly 4,000 planets beyond our solar system, including some that just might have the conditions necessary to support life as we know it. As our technology improves, we should be able to learn more about these worlds and their chances of hosting plants, animals, and maybe even civilizations.

That means if aliens are out there, they could just as easily discover us.

First, they'd need to

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