How long have we got?

How long have we got?


Sapiens by Yuval Noah Harari (what a brilliant name) has been on the best sellers’ list for months. Back in England it’s the focus of my wife’s book club; other friends there have read it and wished to discuss it, but alas I’m at the end of the queue and haven’t read it yet, much to my chagrin. I’m now in Spain observing Jupiter and Saturn and, lo and behold, everyone seems to be reading it here too; the members of the local book club in Tallara are reading it, and everyone seems to have a copy to hand and eager to share some new revelation on almost every page.

So as members of the genus I would think there are few topics of greater interest and intrigue to everyone who has ever contemplated the cosmos than the question, what will happen to life on planet Earth? Everyone alive on the planet today all 7 billion of us, has an interest in the question of Earth’s habitability; and the approximately 100 billion people who have ever lived on the planet would probably have been interested in this as well.

From an astronomer’s viewpoint, the standard feeling about Earth’s habitability goes something like this: The Sun is about half way through its main sequence life, about 4.6 billion years old and with 5 billion years left, so life on Earth should be about half way through, as well, right?

Wrong. The earliest microfossils, primitive, bacteria-like life, date to about 3.8 billion years ago and come from the northern Australian desert. Such cyanobacteria, or ‘blue-green algae’ are larger than ordinary bacteria and can leave behind fossils that scientists can radiometrically date to a very high precision. Moreover, these bacteria create stromatolites, dome-shaped structures that grow in aquatic environments and can leave behind fossilized remains. Dating these colonies of microbes gives us our earliest view of life on Earth. So, we know that life on Earth has been around for at least 3.8 billion years. Why shouldn’t it be around for another 3.8 or even 5 billion years, until the ancient Sun leaves the main sequence and becomes a red giant.

The Homo genus is about 2.5 million years old, but all other versions died out leaving just the one species Homo Sapiens, modern man, us. They had already proved their ability to wipe out most other competitors and certainly today our species yet again demonstrates its murderous intolerance of its fellow man and serious lack of concern for the future wellbeing of the planet, its climate and its resources.

So outside of our own responsibilities which we can at least try to fulfil, what are the other significant problems that will challenge future life on Earth. And bear in mind for all the damage we wreak, human beings are among the more fragile types of life on Earth not the hardiest.

First is the looming rise in the temperature brought to us by the Sun’s radiation output. This will happen long before the Sun swells into a red giant. Second is a decrease in global carbon dioxide, also a result of the Sun’s increasing luminosity, that could cut off the influx of carbon into the planet’s biosphere. Third will be the gradual loss of water on the planet, and the inevitable depletion of the oceans.

The evaporation of water into the space surrounding Earth will mark the final gasp of any life left on the planet. This will occur about 2.5 billion years from now, but the oceans themselves could be largely gone by 1 billion years into the future, a mere blink of the eye in cosmic terms. The planet’s surface temperature will increase dramatically and be too hot for most life, also within a billion years. And the decrease in carbon dioxide and a significant alteration to the atmosphere could take place well before 1 billion years from now.

Considering that life has been on the planet for at least 3.8 billion years, the story of life on our planet could be some 80% over, far more than the halfway mark we tend to think of as an analog to our Sun’s lifetime. And this simply looks at life’s endgame: It does not take into account a host of other mechanisms that could wipe out human civilization. Killer asteroids or comet impacts, a nearby supernova or gamma-ray burst, global warming, and supervolcanoes are just some of the climate changing events that could have a catastrophic impact on our planet and life.

Homo Sapiens as a species is far more likely to be the architect of its own demise than any of the above. We have only been around for 200,000 years and have had and are having a colossal impact on the planet’s wellbeing. We might enjoy another 999,800,000 years aboard planet Earth if we can change our selfish, grasping, short term mindset and learn to husband and share our planet’s resources with the rest of the Earth’s inhabitants, from termites to Blue whales, and from penguins to Polar bears.

Here’s hoping…!

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