The Earth After Us

i-3e74c05bd3373b3b19d8353aac2e3b97-zalasiewicz_the_earth_after_us.jpgJan Zalasiewicz is a geologist active at the University of Leicester. His 2008 book The Earth After Us: What Legacy Will Humans Leave in the Rocks? is an interesting read even though the title does not correspond very well to the contents. Zalasiewicz does answer the question about what legacy humans will leave in the rocks. But on their own, these answers would only provide material for a magazine article. The bulk of the book is instead an introduction to geology which allows the neophyte to understand what will happen to the remains of today’s world as millions of years pass.

Having no geological training, I learned a lot from the book. An idea that I found particularly interesting was that sedimentary strata show a periodicity linked to the Earth’s movement through the solar system, the Milankovitch cycles. Another was that palaeontology’s source material is partly determined by what rocks happen to be currently available for inspection at the surface. Another was that anything that spends a lot of time at the surface of the Earth will soon erode away, which means that a few million years from now it will be impossible to study humanity’s hominid ancestry. Highland ecologies rarely fossilise.

But to me, the book’s take-home message is that humanity’s reign on Earth will mainly show up in the palaeontological record not as a stratum, but as an interface between geological periods. Such a period interface is defined as a place in a stratigraphic column where ecology shifts dramatically, many species go extinct and new ones evolve in their place. Zalasiewicz is quietly convinced that we are a blip on the timeline, with no chance whatsoever of sustaining our great numbers and high technology for more than another few centuries. To future geology, the heyday of Homo sapiens will just be one of several instantaneous mass extinction events in the planet’s history.

See also my review of Alan Weisman’s 2007 book The World Without Us.

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Comments

  1. #1 Bob Carlson
    June 26, 2010

    Zalasiewicz is quietly convinced that we are a blip on the timeline, with no chance whatsoever of sustaining our great numbers and high technology for more than another few centuries.

    Martin Luther King Jr. spoke eloquently on this issue 44 years ago:

    There is no human circumstance more tragic than the persisting existence of a harmful condition for which a remedy is readily available. Family planning, to relate population to world resources, is possible, practical and necessary. Unlike plagues of the dark ages or contemporary diseases we do not yet understand, the modern plague of overpopulation is soluble by means we have discovered and with resources we possess.

  2. #2 Martin R
    June 26, 2010

    Question is, even if we somehow managed to organise a global single-child policy lasting centuries, would the population shrink fast enough to avoid mass deaths?

  3. #3 CherryBomb
    June 26, 2010

    The more archaeologists understand about geology, the better. Even when you talk about time on the scale of a few thousand years, geology is important, at least as a broader context in which to locate your archeology knowledge. Too often, I feel a sense of mutual resentment (if not contempt) between archaeologists and geologists when a broader range of knowledge would be more productive. Everyone is not like this, of course, but enough are.

  4. #4 Prof.Pedant
    June 26, 2010

    Such a period interface is defined as a place in a stratigraphic column where ecology shifts dramatically, many species go extinct and new ones evolve in their place. Zalasiewicz is quietly convinced that we are a blip on the timeline, with no chance whatsoever of sustaining our great numbers and high technology for more than another few centuries.

    Zalasiewicz is certainly correct in assuming that the current period of wastefulness cannot last much longer. I hope that he is wrong about our extinction though. It would be good if humanity is able to grow up and learn to be good stewards of this planet and solar system. Future geology might be even more fascinating if it was a product of eons of thoughtful, respectful, and imaginative, stewardship with a strong emphasis on ecological diversity.

  5. #5 Bob Carlson
    June 26, 2010

    Question is, even if we somehow managed to organise a global single-child policy lasting centuries, would the population shrink fast enough to avoid mass deaths?

    I guess that depends on how long countries like the USA continue to procrastinate on the issue because of the political necessity to preach the need to “grow the economy.” Evidently, for Americans, it is going to take something a lot more drastic than the Gulf of Mexico oil calamity to cause a change in thinking on this issue.

  6. #6 Martin R
    June 27, 2010

    And meanwhile, every Chinese family that can is buying a car and having steak for dinner…

  7. #7 yogi-one
    June 27, 2010

    I hope one day we evolve into an intelligent species.

    If it takes a mass extinction, well, then, that’s what it takes.

  8. #8 Bob Carlson
    June 27, 2010

    From a 2008 Esquire article titled The Globalization of Steak:

    But as with the automobile, the tragedy of the commons looms not far beyond the horizon. Rising Asian demand for beef has led to Amazonian slash-and-burning to create more grazing room for cattle, keeping the price of steak within reach while global temperatures rise. Enjoy it while you can.

  9. #9 Isabel
    June 27, 2010

    It seems that there is so much more we could do.

    Can we organize a global diet conference?

    Do we really have to give up all our luxuries? What alternative conveniences can we design?

    Isn’t buying up rain forest land (or buying off political entities that control the land) within the reach of super-rich individuals. All Bill and melinde Gates are focused on is keeping more humans alive.

    Martin is right that we can’t change human nature, or at least we shouldn’t count on that.

    What if all the people who could comprehend this problem (say,most readers here on Science Blogs)focused on the issue. How many “pressing problems” we obsess over will be moot in the not too distant future?

    Seriously, where are our priorities?

  10. #10 TheBrummell
    June 29, 2010

    Having toured a potash (KCl) mine recently, I was struck by thoughts of our geological legacy. There’s also an interesting bit in the final chapter of Steven Baxter’s novel Evolution which takes place 500 million years in the future, where one very-long-lasting legacy of industrial humanity is a giant open-pit mine.

    Mining and related activities are churning the strata, at least to some extent, and moving rocks around in sufficient quantities that I’d expect things like an iron-mine’s slag pile to persist as a geological feature for hundreds of millions of years, at least. In the potash mine, constant efforts are undertaken to slow (though not cease) the rate at which the tunnels are compressed flat. There’s a well-equiped shop down there, with machine tools and supplies to maintain mine operations, including the fleet of Toyota trucks that cruise up and down the tunnels, and the many-kilometres-long beltways (made from tire rubber, I think) that carry ore to the lifts. All of thse materials would, I think, be maintained in something not too far removed from their current chemical composition, for extremely long periods of time.

    There’s plenty of smelted metal (to take one example) on and near the surface, distributed with a pattern that I expect would tell a far-future geologist a great deal about where and when humans lived. This is in addition to the fossil evidence (i.e. the mass-extinction signal).

    Does Dr. Zalasiewicz’s book discuss issues such as these?

  11. #11 Martin R
    June 29, 2010

    Yes, he does discuss them, and his view is that 100 million years from now all refined metals will have oxidised and all hydrocarbons will have diffused away from their current contexts. He goes on to describe what happens to ceramics and glass. And what happens to culture layers that ride a “tectonic elevator” deep into the crust where the heat and pressure are great. It’s not that everything will be unrecognisable. It’s just going to be fossilised, that is, casts filled with intrusive materials such as pyrite.

    Zalasiewicz’s view appears to be that a mine like the one you describe is so near the surface that not only will it be gone: the entire surrounding rock matrix will have eroded away.

  12. #12 TheBrummell
    June 29, 2010

    Sounds like a really interesting book, I’ll add it to the ever-growing list of “books I really should get around to reading”.

    Surely there would be some geographic variation, possibly predictable even on a 100-million-year scale? I (and the mine I visited) am in central Saskatchewan, Canada. This seems a very geologically stable place, just south of the Canadian Shield with its pre-Cambrian rocks. We descended 1000m to reach the thousands-of-cubic-kilometres salt block that is the ore from which potash is refined. That’s well below the glacial till on top that was ground up and spit out by the last big glaciation. If the top ~900m of material gets eroded away, then yes I would expect the salt block and mine detritus to go away quickly, too, but it does seem unlikely. I am in no way a trained geologist, though, so I really don’t have any idea. I think this area was a shallow sea less than 100 million years ago, so perhaps it will be again.

    My (rambling, incoherent) point is, are there not places, such as cities and towns of the continental interiors, where a signal of human industrial civilization will be visible after 100s of millions of years? A large deposit of high-grade iron oxide, doped with plenty of nickel, aluminium, copper, etc (plus some unusual organics) surrounded by layers conspicuously lacking these materials would be one possible outcome for, say, an automobile junkyard on the edge of a medium-sized town?

    Random silly question: is there a stable-isotope signature associated with industrial metal smelting or hydrocarbon refining? I’m wandering well off into a discussion zone that I should probably just read the book for…

  13. #13 Martin R
    June 30, 2010

    Yes, Zalasiewicz envisions an “Urban Stratum” that will be preserved for instance where a major city is located on a river delta where it gets covered with sediment quickly and sinks into the crust. It will be structured, you’ll be able to identify individual buildings, but since it’ll be identified in section and be covered by tens or hundreds of metres of rock, it’ll be next to impossible to open up any large horizontal excavations in it.

    The important thing about the mine’s preservation won’t be its depth measured from the local surface, but it’s elevation above sea level. Apparently, anything that sticks up to any great extent erodes away with time.

    Isotopes, I don’t know either but I sure think so!

  14. #14 Dunc
    June 30, 2010

    One thing I’ve been thinking about recently: assuming that we either go extinct, or completely lose our current understanding of the world, anybody trying to re-derive ideas like evolution and common descent is going to be facing a much more challenging time. One of the key clues was the spatial distribution of species, and we’ve really messed that one up. We have wallabies running wild in Scotland… How will future naturalists, unaware of the scope of our current ability to transport things around the world on a whim, explain such oddities?

  15. #15 Martin R
    June 30, 2010

    Very true! And then there’s people like me who bloodymindedly obscure humanity’s ancient migration patterns by breeding with someone from the other end of the continent.