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The beginning -

There was no oxygen when Earth was formed. But there was no life either. The atmosphere back then was composed of several gases, including methane and ammonia.

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So what created oxygen on Earth? -

Life produced oxygen through photosynthesis. And in the beginning, it was a bit too much. In the early days, oxygen was pretty deadly. An event known as the Oxygen Catastrophe, or the Great Oxidation Event, confirms this.

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The Oxygen Catastrophe -

This mass extinction event occurred around 2.5 billion years ago. By then, a photosynthesizing bacterium was responsible for releasing high quantities of oxygen into the atmosphere. The result was catastrophic, killing all anaerobic life (organisms that don’t require oxygen to live).

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The Oxygen Catastrophe -

So essentially, this bacterium depended on the Sun to produce oxygen. Despite the oxygenation event, our Sun brought Earth to life…and will eventually destroy it.

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The Sun -

The Sun is becoming brighter as time goes by. It is estimated that since it first ignited, around 4.5 billion years ago, the giant star has become around 30% brighter over the years.

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The Sun -

It is estimated that an extra 10% in brightness, which will occur in the next billion years, will be too much for our planet to handle. This will probably turn us into a dry and lifeless planet, just like Venus. And without life, there isn't oxygen.

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The first elements to be affected -

The increase of the Sun’s brightness will end life on Earth, and oxygen will stop being produced. But the first thing to be affected will not be plants, but rocks.

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Rocks -

There is a complex carbonate-silicate cycle between carbonate minerals (minerals containing CO2) and the atmosphere. With the increase in sunlight, these rocks will end up absorbing more CO2 than they give back.

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When less CO2 becomes a problem -

This disruption in the cycle means that plants will have less CO2 to convert into oxygen. Yes, too much CO2 can lead to global warming, but too little of it will affect photosynthesis and the production of oxygen on Earth.

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Leaves -

Plant leaves produce a natural green compound called chlorophyll. This allows for plants to absorb energy from sunlight. Though if the light they receive is too bright, leaves can also produce free radicals.

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The end of forests -

Excess light means that plants will die and our planet won't be able to sustain forests. This will eventually turn Earth into a desert planet.

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Return to the origins -

A study in the International Journal of Astrobiology points out that “Earth's future biosphere, much like that of the early Earth, will consist of predominantly unicellular microorganisms due to the increased hostility of environmental conditions caused by the Sun as it enters the late stage of its main sequence evolution.”

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Oceans -

Photosynthesis is not just a process that will cease to exist in plants; it will also affect our oceans. Though this process will take longer than it does on land.

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Oceans -

It is estimated that between 50 and 80% of all oxygen on our planet is produced by oceans. Though, like with plants, the increase of sunlight intensity will also dictate the end of oxygen produced by Earth’s large bodies of water.

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Water vapor -

All water will eventually slowly evaporate. And can you guess where all the evaporated water will go? Outer space. Just like oxygen does every day, according to NASA.

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Could plants adapt? -

Nature wouldn’t be nature if it didn’t adapt and fight back, right? Well, this might just happen with plants, with some developing more sophisticated photosynthesis methods.

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Could plants adapt? -

But some plants might even go further, by becoming carnivorous or getting nutrients from fungi in the soil.

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Could plants adapt? -

Plants might also adapt how they protect themselves from the excessive sunlight by producing anthocyanins, which is a sort of natural sunscreen many berries and other fruit and vegetables are rich in.

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Will humans be affected? -

It is very unlikely that humans will still be around when the Sun starts to seriously deteriorate life on Earth.

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Mammals - History tells us that most mammals last for around a million years, so us being the exception to this and surviving for another billion years or so is somewhat unrealistic.

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Finding a new home -

But let's say we do survive until then. We can always hope that before we all start slowly suffocating on Earth, we find a way to travel to other planets!

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Saving Earth -

Instead of fleeing to other planets, we could potentially make adaptations on Earth to accommodate the impending doom that will come with the impact of the Sun on life, and consequently oxygen production.

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Saving Earth -

Excessive levels of CO2 have proven that humans are capable of manipulating the atmosphere. If the lack of CO2 will become a problem in the future, perhaps we can counter the effects of the Sun. After all, for better or worse, we’re pretty good at increasing CO2 levels in the atmosphere!

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Moving Earth -

Another solution would be to physically move our planet further away from the Sun. As crazy as it sounds, scientists have actually considered this hypothesis.

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Moving Earth -

For this to happen, a smaller object would have to repeatedly tug at our planet using gravity. This would make Earth’s orbit gradually shift. The timescale for such an astronomical project? About a billion years.

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Move to Mars -

The Sun might dictate the death of Earth, but equally might bring Mars back to life. Suddenly, moving to our next-door neighbor doesn’t sound so crazy!

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Move to Mars -

Though it will still be pretty cold around the time this happens. Like, Earth’s last ice age levels of cold. But still, we would be able to survive there.

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Life adapts -

Earth’s fate is to be left without oxygen. But as we continue to discover with other planets and on Earth's harshest places, this doesn't necessarily mean the end of life.

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New Earth -

Some life forms, such as extremophiles for instance, can live in the most extreme conditions. So maybe it’s not the end, but the beginning of a new Earth.

Sources: (Scientific American) (New Scientist) (International Journal of Astrobiology 1, 2, and 3) (Grunge)

See also: What would happen if we didn't have the Moon?

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