How to Survive Doomsday - Issue 63: Horizons

How to Survive Doomsday - Issue 63: Horizons

Let’s be optimistic and assume that we manage to avoid a self-inflicted nuclear holocaust, an extinction-sized asteroid, or deadly irradiation from a nearby supernova. That leaves about 6 billion years until the sun turns into a red giant, swelling to the orbit of Earth and melting our planet. Sounds like a lot of time.

But don’t get too relaxed. Doomsday is coming a lot sooner than that.

The Earth is, in some ways, in a precarious spot in the solar system. There’s a range of orbital distances inside which a planet can have both liquid surface water (which is believed to be necessary for life) and enough atmospheric CO2 to carry on photosynthesis. This range is called the photosynthesis habitable zone. The Earth orbits barely within the sun’s zone. Some scientists estimate that the inner edge lies just 7.5 million kilometers away, which is only 5 percent of the distance between the Earth and the sun.

LAST PLANT STANDING: When atmospheric CO2 falls below 150 parts per million, C3 plants like wheat and rice will die off, leaving C4 plants like corn, millet, and weeds.Shutterstock

And that inner edge is moving out. Our sun is a massive ball of gas held…
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