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Time, the Universe and the Whole Darn Thing!
Part One: The Future of the Earth

By Allan Eastman

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Going Down Into That Long Sunset

Silhouette of the climber during sunset

In about 1 billion years, the Sun will be about 10% more luminous.

©iStockphoto.com/Dimitrije Ostojic

So, here we are. Now, where do we go from here?

The Human species, in its various evolutionary forms, has been around on Earth for something like close to 5 Million years. Our particular form, the Homo sapiens, only about the last 200,000 or so of that. We have been very successful on an evolutionary scale - conquering Nature, building civilizations, inventing language, sciences and the arts – although anyone who is honest about it will admit that we are capable of some really terrible things as well and very often, we do the wrong thing for the right reason.

If the Human race continues on far into the future – and there’s no reason to think that some advanced form of us shouldn’t as long as we find the ways to deal with our problems as they come along and we keep exploring – we will have to adapt to the changes the Sun is going to put our planet through.

Old Man Sol is a middle aged star now, getting to be halfway through its existence. It is still fusing hydrogen to helium and it is continually brightening and heating up.

At about 1 Billion Years into the future, the Sun will be about 10% more luminous resulting in the mean temperature on Earth being about 10 degrees hotter. This apparent small variation will make our current debate about climate change look like kid’s stuff. Antarctica will be seriously melting and Oceans will be rising to an alarming extent. All the world’s lower coastlines will disappear under the waves and the continents’ shapes will look far different.

Equatorial regions will be much too hot for Humans to live in, unless we have adapted to do so. But more important, the greatly increased heat will result in much higher atmospheric evaporation and a large amount of the Earth’s water vapor will float off into Space. The result will be a general desertification of all the planet’s landmasses – a planet of sand surrounded by brimming oceans.

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This is the point where whatever Human types still left on Earth really ought to be thinking about getting out of Dodge because it just goes downhill from here.

By 3.5 Billion years on, the Sun is 40% brighter and the temperature is so hot on Earth that the Oceans have evaporated. A thick carbon dioxide based green house gas atmosphere shrouds the planet. To an observer out in Space, Earth is a beautiful reflective disc like the Evening Star but inside its poisonous cloud, it is a molten Hell - like Venus is now. Incredibly hot.

This is pretty much the end of Earth as a home to Life. As the super heated atmosphere bleeds away into Space, all that remains is a barren rock without any atmosphere at all. Any hardy remaining bacteria get progressively sterilized out of existence by intensifying solar radiation. Like the circular nature of life as experienced by an Alzheimer’s sufferer, the planet has returned to what it was like in its early existence.

The Sun keeps going through changes, however. By about 6 Billion years on, it runs out of hydrogen to fuse and gets started on the helium. It heats up again and its outer mantle expands by 50% in size and its brightness doubles.

Add another 1.5 Billion years and the Sun has expanded to 150 times its present size. It is now about 160 Million kilometers in diameter (100 Million Miles). Mercury and Venus are toast. The Sun gives off much more luminosity but because it is so much bigger, the light is red. Sol has become a Red Giant. On the desiccated Earth, the red monstrosity fills half the sky.

But the end of the Sun’s life is drawing near. In only about 300 Million years, it burns through its helium and starts fusing the heavier elements. It shrinks and grows and shrinks and grows as it cycles through the elements, shedding mass with each evolution. During one of the expansions, what’s left of the Earth ends up inside the Sun’s mantle and basically melts, its constituent parts becoming flaming embers blended into the Sun itself. Earth is gone. All the remaining planets in the solar system get fried during this process. Finally, all that is left of the Sun is a dense carbon-oxygen core surrounded by a small envelope of hot helium.

The Sun has become a White Dwarf. Its core is only about 3000 kilometers across but it is incredibly hot and 1000’s of times brighter than now. But it rapidly bleeds off its remaining energy and sinks down through the light scale, becoming blue – yellow –orange – and red. Finally, it is an ash - a Black Dwarf – the cold, dead center of what was once the solar system. After about 12.3 Billion years, it is all over.

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