Earth is Over the Hill

Biologically, Earth has already peaked - perhaps as long as 300 million years ago - and we are already living in a relatively impoverished world. We know that our planet is approximately 4.5 billion years old [...] we can predict that the last animals on this planet will die out as early as 500 million years from now, and possibly much earlier if another great mass extinction, similar to those of the past, once more decimates the planet. If scientists are correct that species diversity and fecundity were actually higher in the past than now, we live not in our planet’s youth but in its middle to old age. Our planet is already in decline.

...biological productivity - the total amount of living plant and animal tissue on Earth - appears to have been higher 200 million to 300 million years ago, when the planet was warmer and richer in atmospheric carbon dioxide than it is today.

Most evidence suggests that life has already existed on Earth longer than it will persist into the future.

...planets, like organisms, have life spans. Astrobiology has evolved with much new information, leading to the inescapable conclusion that habitable worlds can end through a natural evolution akin to aging. Planets have “habitability systems” that are roughly analogous to the organs of a living creature and that eventually fail like those organs.

Earth has a lot of good years left but quality of life becomes a concern before end of life.

The end of Civilization

Earth’s magnetic poles will eventually switch places. This has happened hundreds of times since life emerged on Earth and life has continued. This has not, however, happened since a civilization has emerged to put in place an enormous and enormously complex electromagnetic infrastructure on which their way of life depends.

Poles being on opposite sides of Earth may not present much of a problem (technically they already are on opposite sides) but, in the process of switching, Earth’s magnetic field is weakening and will remain weak for hundreds or even thousands of years leaving us largely unprotected from solar flares and coronal mass ejections as well as other cosmic radiation. Life may be able to carry on without a magnetic field but not our way of life.

Not only does our way of life depend on our electromagnetic infrastructure, so does any ability to monitor or hope of responding to other threats to life on Earth such as geological events, near-Earth objects or subsequent solar events.

Another Mass Extinction

It is an unambiguous fact that very early on our species learned to manipulate the forces of evolution to suit its own purposes, creating varieties of animals and plants that would never have appeared onEarth in the absence of our will. Large-scale bioengineering was under way well before the invention of written language. We call this process “domestication, but it was nothing less than efficient and ruthless bioengineering of food stocks - and the elimination of those species posing a threat to the food stock.

In agriculture, humans have moved from ensuring the survival of certain species that we value over others, to increasing their value through controlled breeding and now directly modifying species on a genetic level to increase their value. The same is being done in species that we value as pets rather than products.

We’ve learned that, just as genetic modification can ensure the survival of those species that we value, the same principles can be applied to ensure the demise of those species that we do not. Gene hacking has already been used to eradicate certain populations of mosquitoes and rats.

In the case of mosquitoes, it’s their ability to spread disease among humans that has made them a target. We don’t yet know what overall effect the mosquitoes’ absence will have on the ecosystem that they were a part of.

In the case of the rats, it’s the humans that have done the ‘spreading’. Rats stowed away on ships have made their way to New Zealand where they have no natural predators. Some native species of birds now face extinction. We don’t yet know what overall effect the rats’ presence will have on the ecosystem that they didn’t naturally evolve as a part of. Nor do we know what the overall effect of eradicating them will be.

The point is that human influence on species and ecosystems has manifested in many different ways throughout human history. The more we become aware of this influence, the more empowered we feel to take advantage or the more obligated we feel to take corrective measures (depending on whether or not we view our influence as positive or negative).

The  Next  Current Ice Age

If you were asked to imagine an ice age, you’d probably imagine sheer cliffs of ice, snow covered mountains and cold blowing winds. That would be an accurate image of a glaciation. To get an accurate image of an ice age doesn’t require much imagination. Look around you anywhere on Earth at any time in the past 2.5 million years. The most recent ice age started in the Paleolithic period and we’re still experiencing it. We’re just between glaciations.

A 400,000-year temperature record derived from measurements on a deep ice core drilled at the Russian Vostok station in Antarctica shows four 100,000-year glacial cycles delineated by 5 sharp spikes in temperature. We are currently standing atop one of those spikes and the unusual width of our particular spike has enabled the rise of civilization.

Overall, Earth has remained cold but, like clockwork, brief interglacial warm periods have occurred roughly at hundred-thousand-year intervals. Ominously, the severity and size of the glaciers produced during each cycle has been increasing through time.

We have about 2000 years before the next one begins the very slow process of knocking over every brick laid in human history. That’s not long in geological terms. The current best explanation for these long-term changes in Earth’s climate are 3 variations in Earth’s orbit and rotation known as the Milankovitch cycles.

The first variation is that the Earth’s orbit around the Sun changes from circular to a pronounced ellipse over a period of about ninety-five thousand years…

The second variation is that while the Moon keeps the tilt of the Earth’s axis relatively stable compared to planets such as Mars, it still varies between 21.8 and 24.4 degrees over a period of forty-one thousand years…

The third variation is that the Earth also wobbles around its axis over a period of twenty-two thousand years: an oscillation like that of a spinning top that scientists call precession. This changes the season when the Earth is closest to the Sun. Today, the Northern Hemisphere has summer and the Southern Hemisphere has winter when our planet is farthest from the Sun. About eleven thousand years from now, the situation will be reversed.

https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/

It’s important to note that these cycles do not explain the current warming of Earth’s climate. This warming is the result of humans burning fossil fuel.

The burning of fossil fuel, of course, is the wildcard in calculating future climate. Will our own folly actually save us from the coming ice?
[…] a new computer model developed by scientists from the University of East Anglia in England has factored in man-made global warming and predicted that this could delay the next ice advance by perhaps as much as fifty thousand years. However, when the ice does return, it will be an even more extreme glaciation that otherwise might have occurred, according to their calculations.

50,000 years might give us enough time to figure out what to do with ourselves during the next glaciation but we’d still need to survive the melting of Earth’s current glaciers. The possible catastrophic effects of this have been described in several scenarios. Here’s one that seems a bit of a paradox.

Agriculture on the European subcontinent is able to support twice the population of North America on a much smaller landmass because its warmth comes from the Gulf Stream. Fresh water from melting glaciers could cause the Gulf Stream to stop short of the European subcontinent. The entire world would experience a sudden change in climate and Europe would go into a deep freeze. Its ability to feed itself would disappear.

And unlike the end of the last glaciation, when there may have been at most 2 million to 3 million humans scattered around the globe and needing to feed themselves, today there are more than 6 billion. [as of 2002]

Incidentally, this is an amazing story. https://www.outsideonline.com/2152131/freezing-death/

Beyond the Next Glaciation

There’s more of course: The return of a single supercontinent and, with it, a stagnant anoxic ocean is the forecast for a quarter billion years in the future. In half a billion years, plate tectonics - the force most crucial to the emergence of complex life - will cease as the geothermal energy that drives plate tectonics fades. In a billion years, the heat from a swelling Sun will make further life on Earth impossible.

After the Sun’s giant phase, it rapidly settles down to become a white dwarf. Its brightness declines thousands of times and it shrinks to only 1 percent of its present diameter…As viewed from Mars, now the closest surviving planet to the sun, it will glow with the brightness of the full Moon. It will be a silvery but cold glow, with no life-supporting heat [...] This is the normal fate of solar systems, as inevitable as our own individual deaths. The galaxy contains billions of white dwarfs, many of them just tombstones for worlds like our own.

Planet B?

A person looking at scale depictions of Earth and Mars might see Mars as about half the size of Earth. This is true of the diameter but, on a sphere, the outer half of that diameter has far more volume than the inner half. So the mass of Mars is only about 15% that of Earth!

The surface pressure is similar to the air on Earth at 30 kilometers, or more than three times the height of Mt. Everest. There is no oxygen. There is no food. There is no surface water, and it never gets warm. Deadly ultraviolet light from the Sun bakes the land.

We have difficulty sustaining the environment of our home planet, let alone successfully manipulating that of another. Would anyone really want to relocate to a planet with half our gravity and a Sun half as bright? Even on our own crowded planet, vast reaches of the Arctic and Sahara remain almost uninhabited. Will humans persist in the hundreds or thousands of years it would take to terraform Mars?

Going to Mars is much more difficult and dangerous than going to the Moon. You can get to the Moon in three days, but it takes months to reach Mars. Round-trip mission times are on the order of a year or more. Astronauts are exposed to potentially lethal cosmic rays from the Sun and have to survive long periods of low gravity in an environment that produces irreversible loss of bone mass. The degradation of the human body in space has been feverishly worked on for more than forty years, and yet there is still no clear solution to the problem of long-term survival of humans in space.

Even with the greatest of care and a budget of billions of dollars, Hubble was put into space with a misshaped mirror, solar panels that flapped every time they passed in and out of the sunlight, and gyroscopes that failed at a much higher rate than expected. Hubble became a huge success only because it was so close to the ground that the space shuttle could carry up heroic astronaut crews on repeated repair and refurbish missions. In deep space, repair missions are not practical […] Since 1959, thirty-five missions have been sent to Mars. Over half have failed. As technology has continued to advance, the success rate has not improved. Can we ever make traveling to Mars as safe as traveling on a plane or even flying in the space shuttle? Probably not.

To do it Properly…

Maybe we have an idea about how to engineer an atmosphere and liquid water on Mars. But, if we can’t engineer a magnetic field, they’ll just (continue to) be lost to space. And, if we can’t engineer plate tectonics, the martian landscape will be weathered to oblivion with no way to sustain the land masses and topography necessary to facilitate temperature regulation and weather patterns that will allow complex ecosystems to thrive. And humans can’t thrive without complex ecosystems.

What we really need to engineer on Mars is a liquid metal core. One thing that seems to have worked in the past is to clobber one planet with another one. Our current best model of how Earth was formed involves Earth being struck by another Mars-sized planet that developed in the same orbit.

Because Mars is so much less massive than the Earth, even if we set out to terraform it in the same way as Earth (ie. by clobbering it with a Mars-sized celestial body), we would need to do that 5 times over. But there aren’t 6 of Mars out there. Even if we threw every object in the asteroid belt and every moon of Jupiter at it, we’d only get to about 17% of Earth’s mass.

Other famous places that might possibly support life also seem to be unlikely sites for future human colonization. Titan, Ganymede, Callisto, and Triton are all quite different bodies from Earth. It is more likely that humans will transform into some strange kind of superbeings that could thrive in hostile environments than it is that these distant moons could be made at all Earth-like.

If that’s the case, we might as well just continue to inhabit Earth as it becomes an increasingly hostile environment.

Can we take it with us?

There’s another idea worth mentioning here if only for eyebrow elevation. It’s the idea of coordinating numerous gravity assists from a 100-km wide comet to nudge the Earth ever outward as the Sun increases in intensity. One fly-by of the comet would occur once every 6,000 years and it would take a million of them to get Earth into the same orbit as Mars. If we get it wrong even once, the impact of a 100-km wide comet would sterilize life on Earth down to the microbial level. Even if we get it right every time, we’ll likely throw our moon out of orbit which would also be catastrophic for life on earth. We needn’t concern ourselves about what to do with the planet currently occupying Mars’ orbit. By the time we reach it in 6 billion years, the intensity of the Sun will make life on any planet at that distance impossible.

Conclusion

I rushed a bit through the list of longer-term challenges Earth will face because, before Earth runs out of challenges to deal with, it will run out of beings with any ability or sense of responsibility for dealing with them. Ultimately, the mortality of Earth - like our own individual mortality - is something we will have to  accept  embrace.

Of course we should do everything we can to survive as long as we can. And we should do everything we can to ensure that survival doesn’t just amount to prolonged suffering. We may be able and willing survive long enough to develop now unthinkable ways to address issues like the waning magnetic field, an imminent glaciation or even the swelling of the Sun. But, only if we’re able to address the more immediate challenges that we face.

It’s somewhat fortunate that the most pressing challenge, global warming, also seems to be the only one that humans currently have any capacity to deal with. And we’d better get focused because there really doesn’t seem to be a ‘Planet B’ within our reach.

Even if there were, it would amount to a very expensive camping trip to a very hostile environment. Camping can be fun - even camping in a hostile environment - but you don’t start loading up your camping gear when you hear the fire alarm going off in the kitchen, you grab a fire extinguisher.