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Although our planet is thought to have had about a 2:1 ratio of oceans to continents throughout its history, there was a period from about 2.4 to 2.1 billion years ago where the surface was 100% covered in ice: a Snowball Earth scenario. Could our planet, despite global warming, actually become cooler over the next 20,000 years? (NASA)

Sure, we’re warming now. But will this continue, or will natural factors change things?

According to our best understanding of Earth’s climate, the global average temperature has increased significantly over the past ~140 years: the amount of time for which a reliable, direct temperature record exists. …

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If a black hole were to appear between the Earth and an observer, the Earth would appear gravitationally lensed in a fashion similar to this, dependent on the Earth’s position relative to the black hole and the observer. If a black hole were to form from the Earth itself, it would create an event horizon just 1.7 centimeters in diameter. (ANDREW HAMILTON / JILA / UNIVERSITY OF COLORADO)

Yes, we’d all die. But for 21 minutes, we’d have the ride of a lifetime.

One of the most remarkable facts about the Universe is this: in the absence of any other forces or interactions, if you start with any initial configuration of gravitationally bound masses at rest, they will inevitably collapse to form a black hole. A straightforward prediction of Einstein’s equations, it was Roger Penrose’s Nobel-winning work that not only demonstrated that black holes could realistically form in our Universe, but showed us how.

As it turns out, gravity doesn’t need to be the only force: just the dominant one. As the matter collapses, it crosses a critical threshold for the amount of mass within a certain volume, leading to the formation of an event horizon. Eventually, some time later, any object at rest — no matter how far away from the event horizon it initially was — will cross that horizon and encounter the central singularity. …

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This launch of the space shuttle Columbia in 1992 shows that acceleration isn’t just instantaneous for a rocket, but occurs over a long period of time spanning many minutes. The acceleration that someone on board this rocket would feel is downward: in the opposite direction of the rocket’s acceleration. No spacecraft has yet taken humans more than ~400,000 km from Earth. (NASA)

We’re Earth’s first intelligent, technologically advanced civilization. But maybe not the last.

For most of our planet’s history, life in some form has existed on our world. Planet Earth formed some 4.5 billion years ago in the infancy of our Solar System, and life surely took hold on our world not long after. The oldest surviving fossils go back 3.8 billion years, with carbon-based inclusions in rock — arguably originating from Earth’s earliest life forms — dating back more than 4 billion years. Life has transformed our planet’s atmosphere while surviving, thriving, and becoming complex and differentiated.

Just over half-a-billion years ago, the Cambrian explosion occurred, giving rise to a wide variety of megafaunal animals whose descendants have persisted on our world ever since. During all that time, only human beings, which evolved just a few hundred thousand years ago, became a technologically advanced civilization. In the 20th century, we finally reached space, and now have the capacity to begin reaching for the stars. But are human beings the Earth’s best chance to become a spacefaring planet? Or will another civilization after we’re gone be better equipped for that challenge? Although we frequently assume we’re Earth’s best (and only) opportunity, that assumption may be incorrect. …


Ethan Siegel

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.

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