Marcelo Gleiser

For this post-Thanksgiving week, I'd like to suggest a remarkable video produced over two decades by NASA scientists.

Satellites monitored populations of plant life on land and oceans, mapping variations of green regions of vegetation and snow cover on the North and South Poles. As seasons pass, we witness a rhythmic dance between white and green, as if the planet itself were breathing.

Since my last post was on Earth's hosting of life, it's natural to follow with a discussion of life elsewhere.

From the outset, we must state two essential facts: first, that we have no concrete evidence that intelligent aliens have ever visited our planet; and, second, that we have no evidence that there is life outside Earth, intelligent or not.

Let's look into the alien visitation question first — and leave the question of life elsewhere for another time.

Living in cities or suburbs, amid the race of everyday routine, we have little time to care about what goes on at the planetary level — or about the uniqueness of our planet.

As Europe was being torn apart in the early 17th century by conflicts between Catholics and Protestants — that would lead to the devastating Thirty Years War in 1618 — the German astronomer Johannes Kepler wrote:

"When the storm rages and the shipwreck of the state threatens, we can do nothing more worthy than to sink the anchor of our peaceful studies into the ground of eternity."

Some 130 million years ago, when dinosaurs roamed Earth, two dead stars in a far-away galaxy collided violently, after spiraling around each other for millions of years.

The dead stars were neutron stars, exotic objects the size of Mount Everest and with the mass of the sun. Being this small and dense, the gravitational force is fierce. Someone once compared the pull of gravity near the surface of a neutron star to having all the population of Paris tied to your feet.

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