When astronaut Jim Lovell saw Earth outside his window during Apollo 8, the moment forever changed him.

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"People often say, 'I hope to go to heaven when I die,'" Lovell previously told Business Insider. "In reality, if you think about it, you go to heaven when you're born."

Lovell was referring to the humbling truth about our fragile existence: Life exists here only because it teeters in a delicate and truly improbable balance. Our atmosphere, proximity to the sun, and countless other beautiful coincidences not only permit living things to survive and evolve, but also to thrive.

And yet, here we are, sitting at desks and in coffee shops and walking down the street like it isn't some kind of extraordinary miracle.

But all good things must come to an end.

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One day Earth will be inhospitable to anything resembling life as we know it.

The life on this planet likely won't cease until billions of years from now. But, depending on how the stars align — in some cases, literally — it could also happen tomorrow or anytime in between.

Here are the many ways scientists believe the Earth as we know it could die.

This story was originally published on March 30, 2016 at 8:55 a.m. ET and updated with new information.

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1) The Earth's molten core might cool.

Earth is surrounded by a protective magnetic shield, called the magnetosphere.

The human species will likely destroy itself long before the sun kills everyone on Earth, a Harvard sciions of years in the future, the sun will destroy our planet.

As the star runs out of hydrogen and helium atoms to burn in its core, it glows brighter and brighter. Eventually, the sun will bombard Earth with enough high-energy light to incinerate the world's oceans, melt the polar ice caps, and strip our atmosphere of all moisture — effectively killing all life.

But don't fret. We'll likely all be dead by then anyway.

A BBC reporter recently asked Harvard astronomer Avi Loeb what a possible solution to humanity's imminent demise might be.

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Loeb outlined his response in a recent Scientific American blog post, where he stated how imperative it is for our species to relocate to other parts of the universe that are less close to our sun's vacillating brightness.

The astronomer doesn't want us to remain shackled to existing planets and moons, either — he said it'd be best if humanity could "manufacture a gigantic structure that will be able [to maneuver] the optimal orbital distance at any given time" from the sun's deadly energy.

Once we successfully colonize both nearby and interstellar space, Loeb added, we can make genetically identical copies of ourselves and "the flora and fauna we hold dear" to seed other planets with life.

That being said, Loeb ended his blog post on a depressing note. In his opinion, humanity will wipe itself out long before the sun might.