“Planetary Changes from Deep Time to the 4th Kind”
In Plain English:
Life doesn’t just adapt to geochemical features; it transforms them simply by…living.
What it covered:
Climate shapes life. This is a fact. But when you get right down to it, life is not a fragile, softly-treading phenomenon; every living cell is an interlocking network of chemical reactions. Nutrients and resources are taken in; other chemicals get spewed out.
It would be rather amazing if all those living organisms didn’t have some effect on the non-living environment. But what kinds of impacts? And how can we, as humans with advanced technology, understand and predict the effects our actions will have on the environment?
These are the questions being addressed by The Planets and Life Series at MIT, and the kick-off event, held back in September (unfortunately, I do not get paid to write this blog) was a doozy.
It was a double feature talk, featuring lectures by Andrew Knoll of Harvard’s Earth and Planetary Sciences Department and David Grinspoon of The Planetary Science Institute and The Library of Congress. Knoll investigates the deep history of life on Earth by studying the geological record, and Grinspoon is an astrobiologist who comes up with ideas about what life would most likely be like on other planets.
Part I: A Really Trippy & Brief Overview of Life’s Early History
Knoll was up first. Establishing the exact chronology of life is difficult, he explained, but we do know that life has been around almost twice as long as the oxygen-rich atmosphere that supports animal life today.
Studies of rock formations known as stromatolites, which are believed to be the remnants of ancient bacterial reefs (before there was coral; bacteria clumped together to fill that niche), have established that bacteria were alive and kicking 3.4 billion years ago, and they didn’t even need oxygen to do it. Because rocks from that eon, known as the Proterozoic, contain types of rocks that only form in the absence of atmospheric oxygen but also contain sulfur compounds that would have been produced by anoxic photosynthesis. (In regular photosynthesis, the cell takes in carbon dioxide and water and produces oxygen gas and ATP, the molecule that living cells use for fuel. In anoxic photosynthesis, the cells use hydrogen sulfide instead of water, and produce sulfate ions instead of oxygen.)
Some scientists estimate that around 3 billion years ago, levels of oxygen gas in the atmosphere were less than 1% of what they are today. But then, something changed.
Specifically, a group of organisms known as the cyanobacteria started using the water-oxygen-based photosynthesis method. At first they would have lived in isolated oxygen-rich “oasises”, but as the cyanobacteria became more successful, levels of oxygen began to rise.
And once that started, everything changed. Because there was extra oxygen gas available, some organisms began to use O2 as their oxygen source. And since oxygen is a highly reactive element, it made a good power source. Oxygen-consuming bacteria and archaea were able to evolve larger and more complex forms. And then eventually, they evolved the ability to do something really crazy.
They became able to engulf things. Which meant those lucky organisms didn’t have to photosynthesize their own food anymore; they could eat other cells.
And then an even stranger thing happened: Once in a blue moon, one of the smaller bacteria that the big oxygen-burning archaea ingested would survive the engulfment and become an integral organ within the cell. That is how chloroplasts and mitochondria came to be.
From there, life got even more complicated.
If you are an autotroph (an organism that can produce its own food, usually through photosynthesis), the best way to avoid to getting engulfed is to become too large to engulf. And in most cases, being multi-cellular is much more efficient than being an enormous single cell.
However, heterotrophs (organisms that get their food by eating and/or absorbing other organisms) can also play the multicellular game. The two most popular flavors of multicellular heterotroph are animal and fungal. Animals first emerged around 800 million years ago, according to most estimates, and their/our rise would never have been possible if oxygenic photosynthesizers like the cyanobacteria hadn’t produced tons and tons of oxygen gas for our cells to burn.
But all this expansion and diversification had a cost. The vast majority of Proterozoic life had evolved to live in an anoxic environment. To them, the plumes of O2 the cyanobacteria produced were poisonous.
The biochemical event that made life as we know it possible was also the probable cause of a mass extinction. Chances are we’ll never know much about the anoxic species that the cyanobacteria inadvertently killed off- they were so small and it was so long ago that it’s hard to find concrete traces of them in the rocks- but if they hadn’t died, there might not have been room for animals to take over.
And on that note, we segued into…
Part II: An Astrobiologist Riffs on Whether We (21st Century Humans) Are Like Cyanobacteria
Human activity is altering the biosphere at the planetary scale. We have increased the amount of carbon dioxide in the air, we have acidified oceans, we have splintered ecosystems, and we are showing no signs of slowing down.
Are the effects we’re having on the biosphere the product of intelligence? And if our intelligence makes us so smart that we can render our planet uninhabitable, is our intelligence really an evolutionary advantage? And given that we seem to be burning out our own resources so quickly, will we stick around long enough for alien civilizations to find us?
These are the kinds of questions that astrobiologists like David Grinspoon pose to MIT audiences.
Astrobiology is the highly speculative but endlessly fascinating field that studies how life begins on planets and what determines life’s ability to sustain itself.
Grinspoon presented us with a model where we posited four possible types of global planetary climate change:
- Type 1: Natural catastrophes like hypervolcanoes, asteroid impacts, etc.
- Type 2: Biological catastrophes, like that time the cyanobacteria started dumping tons of oxygen into the atmosphere
- Type 3: Inadventent catrastophes, Like that time when some really smart hominids made a bunch of machines, cut down a bunch of trees, and then either didn’t notice or deliberately ignored the impacts of their actions
- And, finally, Type 4: Intentional global change, where a really smart species gains the power/mechanical know-how to implement global change but does uses its power in a self-aware and sustainable way.
Type 4 is aspirational. It is up to MIT students (and other assorted smart people around the planet) to make it happen.
We are too far gone, Grinspoon argued, for things to go back to the way they were before humans existed. “We’re basically gods,” he said. “We might as well get good at it.”
But on the bright side, when we look at the atmospheres of other planets for signs of life, the planets that show signs of intentional change are the planets most likely to play host to organisms who can actually talk to us. Natural catastrophes happen everywhere, whether there’s life or not. On planets exhibiting symptoms of inadvertent catastrophe, there’s a good chance our potential alien neighbors could burn themselves out before we get a chance to meet them. But signs of deliberate intelligence? Those are going to be rare.
We should probably try to make Earth a Type 4 planet, so the human race can stick around long enough to find them.
My Personal Take:
My literature and philosophy major friends are fond of condescendingly reminding me that nature is infinitely more powerful than we are and that there’s no way science could ever hope to control or understand everything in it.
While there is so truth to that assertion (In a one-on-one confrontation between a single unsheltered human and Nature, Nature will usually win), I’ve always felt that that attitude allows a lot of first-world humanities majors to forget how powerful contemporary technologically-fortified humans actually are.
It also reinforces the notion that humans are somehow separate from “Nature”, when in fact, we not only part of Nature, but also one of the “power players” of this epoch.
So even though some of the stuff Grinspoon was saying was fairly out-there, hearing someone present the notion of humans taking environmental conditions into their own hands, not as a hubristic fantasy, but rather as something we are very capable of and, to some extent, obligated to do was refreshing.
A classic MIT moment of simultaneously having my ego built up by hope that I can contribute to something amazing and torn down by the realization that the idea is almost impossible.
Knoll’s talk was pretty amazing, too. Although I’ve been a Lynn Margulis* fangirl for a longtime, I’d never really thought about how much would have to change at the biochemical level in order for engulfing to happen. Growing large enough to swallow your prey is hard work, even before you factor in the fact that you might need a way to chase them. And even then, only certain types of cell membranes can stretch far enough to surround a prey item and absorb it into the cell body.
Guys, the fact that eating ever evolved in the first place is actually kind of amazing!
But as much as this talk made me happy, in the back of my head I couldn’t help but be sad that so few people will ever get the chance to learn about this stuff. Creationists have made such a huge fuss that in some places, even getting Darwin into the biology classrooms is difficult. People get so focused on making the basic tenets of evolution are given their due that no one bothers to think, “Hey! Maybe we should teach middle school kids about this really cool evolutionary event that explains why the diagrams of our cells’ insides are so confusing!”
And climate change deniers have made such a fuss that trying to have a public discussion about Gaia Theory and how we might alter our behavior to be less biochemically disastrous is all but impossible.
You almost have to be at an MIT-caliber science center in order to have an intelligent conversation about Lynn Margulis’ ideas. And that makes me sad. Because not only was she (in my opinion) one of the most important thinkers of the twentieth century, having conversations about these ideas could actually yield behavioral changes, technological ideas, and cultural shifts that could actually save billions of lives.
But it’s going to be hard to expand that conversation outside of the environmental science community unless there’s a serious and concerted campaign to get endosymbiosis and Gaia theory into popular discourse and middle school biology classes.
Oy. Us 21st century science writers have so much s*** to do.
*Lynn Margulis is the scientist who originated The Theory of Endosymbiosis, or the idea that chloroplasts and mitochondria are bacteria our ancient ancestors engulfed and assimilated, and one of the key early contributors to The Gaia Hypothesis, the idea that life actively transforms its abiotic environment into a system that suits life’s needs.
She is also one of the scientists on my “Rosalind Franklin List.” That’s a list of vitally important women in science that I keep in my head. If I mention one of the scientists on that list and someone asks me who they are, I tell them they owe me ten pushups, glare at them until they do it, and then explain. Because there are a few women in science history that everyone who subscribes to evolution and/or has benefitted from 20th century medicine should just know. Especially if they are people who know who Darwin, Einstein, Watson/Crick, Newton, Sacks, Gould, Pauling, etc. are.
I’m not going to disclose the entire list, because that would kind of defeat the point. But yeah, as far as I’m concerned, Lynn Margulis, Rosalind Franklin, and their ilk should not need introductions.
Biggest Misconception to Avoid:
Gaia Theory has a lot of different versions, with varying levels of scientific evidence and crazy.
Very few people would assert that cyanobacteria deliberately and knowingly destroyed the ancient Earth’s atmosphere in order to suit their needs, but on the flip side, arguing that the biochemical processes of life have a negligible impact on the abiotic environment is an equally ridiculous argument.
Grinspoon: “[The cyanobacteria] were innocently exploiting a new energy resource and caused a global climate catastrophe! Oxygen was poisonous to most lifeforms on Earth. They caused death and destruction on an unprecedented scale. They created a Snowball Earth…I mean, you think Exxon Mobil and Haliburton are bad?! Look at what there guys did…
Well, you can’t really call them irresponsible because they’re bacteria.”
Runner-Up One Liners:
- Knoll [on gaps in the fossil record]: “Sadly, DNA are proteins are not likely to be preserved. They’re simply too good to eat.”
- Grinspoon: “The cyanobacteria were like, ‘Let’s eat sunshine! Let’s make oxygen!’ Not knowing that oxygen would create all of this death and destruction.”
- Knoll [on his colleagues]: “There are three kinds of field biologists: the one that gets out of the car [which is stuck in the mud] and fixes it, the one who watches, and the one who goes and gets the camera.
- Grinspoon [on what aliens would say if they’d been monitoring the Earth]: “Have you noticed that something really weird is happening with the Earth?…I mean, seriously. If you’re an alien who’s been watching the Earth for 3 billion years, you’ve seen some stuff…the emergence of life…volcanism…a big asteroid going whack!…but at night, it’s always been dark. Now you’d be going, ‘Whoah…’”
Best Audience Question (yielding a random story about Lynn Margulis):
Audience member: Cyanobacteria irrevocably changed the biosphere. And I’m wondering are the environmental changes we’re creating on the same scale as the oxygenation event. How much are we like our irresponsible hero?
Knoll: Lynn Margulis– Rest her soul- used to call oxygenation the “Proterozoic Holocaust”. Which I think is just a terrible mixture of ideas….But you can’t have a major geochemical change like that without a mass extinction. That’s just what happens. Lots of death and then the survivors fashion a new biosphere, which may be very different.
Grinspoon: Well, we wouldn’t be sitting here talking about this without the cyanobacteria, so I can’t be too hard on them…
Knoll: We’d be lucky if we survived the next 100 years without a geologically significant extinction. Whether it’s on the scale of the P-T extinction is less certain. We’re certainly seeing a lot of the same effects: ocean acidification, global warming,…this is exactly what happened at the end of the Permian.
(As always, the questions and responses are paraphrased based off of detailled notes I took at the talk.)
- Anoxic = lacking, or occuring in the absence of, oxygen
- Endosymbiosis = the evolutionary event where a few species of ancient bacteria got engulfed by archaea and became vital cellular organs instead of food. This is by far the most widely accepted explanation of how chlorophyls and mitochondria evolved.
- Gaia Hypothesis or Gaia Theory = Scientific idea, which is on that awkward cusp where some scientists think it’s a theory and others think it’s a hypothesis. (Remember: In scientist-talk, the word theory means “hypothesis that people have failed to disprove so many times that we can safely consider it a fact”.) States that living organisms biochemically regulate their entire environment.
- Cyanobacteria = also known as blue-green algae, even though they’re an ancient line of bacteria. The first organisms to pioneer a photosynthesis method that produces oxygen gas as a biproduct. The “Irresponsible Heroes” whose actions marked the end of the Proterozoic eon.
- Oxygenation = In this context, the major biogeochemical event that occurred when cyanobacteria started producing O2 gas. More broadly, it can refer to any time oxygen-levels in a system increase.
- Proterozoic eon = period of time between 2.5 billion and 542 million years ago. Life existed, but as far as we know, everybody back then was a single-celled organism. Eukaryotes emerged about halfway through it.
- Anthropocene = present period of geologic time. Began in mid-1800s when the human Industrial Revolution began dramatically altering the composition of Earth’s atmosphere.
- Permian-Triassic Extinction = most lethal mass extinction in Earth’s post-oxygenation history. Early symptoms included increased atmospheric CO2 and ocean acidification. It’s also the mass extinction that most closely resembles today’s “climate change”.
Tl;dr: Life can biochemically alter the environment at a global scale. Cyanobacteria did it a long time ago and killed off a huge number of organisms, but on the bright side, that extinction made room for oxygen-breathers like us!
On the not-so-bright side, we’re biochemically altering the environment right now.