Life on Earth was victim of its own success!

[GrandMasterTerwynn]

According to a new study.

How Lowly Bacteria Froze Earth Solid
By Robert Roy Britt
LiveScience Senior Writer
posted: 01 August 2005
02:00 pm ET


Earth has been through many cold spells since its birth 4.5 billion years ago. Scientists say some drastic episodes froze the planet all the way to the equator.

Yet these "snowball Earth" scenarios expose a gaping lack of understanding: What caused them?

Lowly bacteria, according to a new study.

In the first and worst snowball episode, 2.3 billion years ago, bacteria suddenly developed the ability to break down water and release oxygen. The influx of oxygen destroyed methane in the atmosphere, which had acted as a blanket to keep the planet warm.

The idea is presented in the latest issue of the Proceedings of the National Academy of Sciences by researchers at Caltech.

In modelling the scenario, the scientists say Earth's exact position from the Sun is the only thing that saved the planet from a permanent deep-freeze.

And, they caution, it could happen again.

Back then

Before the first snowball event, the Sun was only 85 percent as bright as now. But the planet was temperate, much like today. Scientists believe that's because the atmosphere was loaded with methane, a greenhouse gas. It's the same gas used to heat many homes.

Then along came cyanobacteria, which evolved into the first organisms to use water in photosynthesis, releasing oxygen as a byproduct. Scientists had thought the shift might have occured perhaps as far back as 3.8 billion years ago.

But the Caltech scientists searched ancient rocks for clues and found no evidence for the change prior to 2.3 billion years ago.

Here's what they think happened:

A regular old Ice Age set in, and glaciers advanced to middle-latitudes as they would many times in geologic history. When the glaciers retreated back toward the poles, they scoured the land and released abunant nutrients into the oceans.

There were no plants or animals back then. The cyanobacteria, with their newly developed ability to make oxygen, fed off the fresh flow of nutrients, the thinking goes, and their numbers exploded.

And things, well, they snowballed from there.

Minnesota all over

"Their greater range should have allowed the cyanobacteria to come to dominate life on Earth quickly and start releasing large amounts of oxygen," said study team member Robert Kopp, a Caltech graduate student.

Computer modeling shows that most of the atmospheric methane may have been destroyed within 100,000 years, certainly within a several million years. Methane is far more insulating than carbon dioxide, another greenhouse gas.

Global temperatures plummeted to minus 58 Fahrenheit (-50 C). Ice at the equator was a mile thick.

Most organisms died. Biology clung to hydrothermal vents or survived underground, Kopp and his colleagues say. Even today, life has shown itself to be incredibly resilient, eating rocks, swimming in boiling water and enduring thousands of years in the deep freeze.

Then evolution pulled another trick, the scientsits figure. Some of the organisms that did survive adapted to breathe oxygen, now that there was a lot of it.

It was this ability to use oxygen that allowed life to evolve to more complex forms, the scientists say.

Then what?

That leaves the question of how we got out of that frozen mess the bacteria got us into.

Eventually, the scientists say, the changed biology and chemistry caused carbon dioxide to build up enough to generate another greenhouse period. Temperatures climbed to perhaps 122 Fahrenheit (50 C) around the globe, evidence indicates.

"It was a close call to a planetary destruction," says Kopp's supervising professor, Joe Kirschvink. "If Earth had been a bit further from the Sun, the temperature at the poles could have dropped enough to freeze the carbon dioxide into dry ice, robbing us of this greenhouse escape from snowball Earth."

Kirschvink sees a lesson for industrial humans. While a snowball Earth could not develop in a generation and probably not even within a few hundred years, it looms as a long-term possibility.

"We could still go into snowball if we goof up the environment badly enough," he said today.

"We haven't had a snowball in the past 630 million years, and because the Sun is warmer now it may be harder to get into the right condition," Kirschvink said. "But if it ever happens, all life on Earth would likely be destroyed. We could probably get out only by becoming a runaway greenhouse planet like Venus."

Interesting stuff.

[Erik von Nein]

That's wild. I always love hearing about what bacteria can do for (or, rather, to) us. Best not to piss off the bacteria, now!

[Darth Wong]

I can't help but think that someday, some alien researcher is going to be picking over the bones of our civilization and saying to himself: "stupid fuckers."

[Dakarne]

I can't help but think that someday, some alien researcher is going to be picking over the bones of our civilization and saying to himself: "stupid fuckers."

If you don't mind, I'm sigging that...

[wolveraptor]

I didn't know bacteria could chemically break apart water. What happened to all that hydrogen?

Also, this may mean that life-friendly planets are much rarer than previously thought, if bacteria-like creatures can so easily kill themselves without the safety net of perfect distance.

[GrandMasterTerwynn]

I didn't know bacteria could chemically break apart water. What happened to all that hydrogen?

Also, this may mean that life-friendly planets are much rarer than previously thought, if bacteria-like creatures can so easily kill themselves without the safety net of perfect distance.

The hydrogen was probably used by the critters in making hydrocarbons, which are the most basic component molecules of life (as they are tied up in proteins and amino acids.)

Any they didn't use would've escaped Earth's atmosphere in very short order, given that hydrogen has one-sixteenth the mass of oxygen, so it doesn't take a lot of energy to kick it up to Earth's escape velocity.

[genkkov]

Of course bacteria break apart water...

photosynthesis
CO2 + H2O --> C6H12O6 + O2

I don't know of any biochemical reactions that use molecular hydrogen. If you know of one, please educate me.
Hydrocarbons are not in proteins. Proteins are made of amino acids, which are not hydrocarbons. Hydrocarbons are made of hydrogen and carbon, i.e. methane (CH4) or propane (C3H8).

Now that the freshman biochem is out of the way...

The biggest crisis that life on earth has ever faced was the permian extinction, in which something like 99.9% of species at the time (which I think is about equal to 99% of all species that have ever existed) became extinct due to the increasing concentration of molecular oxygen (which is very toxic if you can't handle it) in the atmosphere, and forced a change from a reductive metabolism to oxidative metabolism. Life survived this, because life by its very nature is adaptable. Some species were already suited to survive increased O2 levels, and those species filled the niches of those who could not survive. This is evolution, and if there's one thing that would be consistent about life on this world or any other, it is natural selection with modification, especially in the face of a strong selective stimulus.

[genkkov]

oops, did I say permian...


My bad, meant proterozoic. My geology not so good.

[Winston Blake]

So i have to worry about global cooling now? Runaway greenhouse effect is a good thing? Oh well, i'm sure in a few decades those silly scientist-types with their big words will turn around again with another 'Um, actually...'.

BTW, i just this idea: if a change in the atmosphere's composition is what allowed the development of vastly more complex and diverse life (including human intelligence) from nothing but lowly cyanobacteria, then what if the current conditions are somehow preventing the development of a different kind of metabolism that could allow for a weird, 'better' type of life?

[Grandmaster Jogurt]

So i have to worry about global cooling now? Runaway greenhouse effect is a good thing? Oh well, i'm sure in a few decades those silly scientist-types with their big words will turn around again with another 'Um, actually...'.

BTW, i just this idea: if a change in the atmosphere's composition is what allowed the development of vastly more complex and diverse life (including human intelligence) from nothing but lowly cyanobacteria, then what if the current conditions are somehow preventing the development of a different kind of metabolism that could allow for a weird, 'better' type of life?

Evolution isn't something that makes things "better" every time it happens. If we had another atmospheric change, the new species wouldn't be intrinsically better, simply better adapted to the new conditions. Sure, there's a chance that it could eventually lead more diverse and complex global life (if that's what you meant by "better"), but it could also leave Earth with nothing but a few varieties of bacteria. Evolutionary change isn't a straight path to sapience and beyond.

[Winston Blake]

BTW, i just this idea: if a change in the atmosphere's composition is what allowed the development of vastly more complex and diverse life (including human intelligence) from nothing but lowly cyanobacteria, then what if the current conditions are somehow preventing the development of a different kind of metabolism that could allow for a weird, 'better' type of life?

Evolution isn't something that makes things "better" every time it happens. If we had another atmospheric change, the new species wouldn't be intrinsically better, simply better adapted to the new conditions. Sure, there's a chance that it could eventually lead more diverse and complex global life (if that's what you meant by "better"), but it could also leave Earth with nothing but a few varieties of bacteria. Evolutionary change isn't a straight path to sapience and beyond.

Yes, i know all that. I wasn't saying 'If the atmosphere changed, would the animals talk and everybody transmogrify into angels' i was saying 'Is the current set up already optimal? (as far as diversity and complexity are 'good things', e.g. current biosphere vs pure cyanobacteria)

[Typhonis 1]

Could be worse. Imagine what Earth would be like if say a 1000 kn asteoid hit it.

[genkkov]

Is the current setup optimal for complex life?

Of course it is, complex life evolved in this current setup. If it had been the other way round we'd be saying that the other way is optimal for complex life. I don't think that there's anything intrinsic in our metabolism that makes it friendly to multicellularity other than it's efficiency, which is a product of evolution.

Also, most of the diversity on earth is cyanobacteria. There are orders of magnitude more bacterial species than eukaryotic species. It is an interesting exobiological question though, is the march of complexity inevitable, and if not, what conditions would increase the chances of complex life developing?

[Admiral Valdemar]

I'd have to say that it's not as cut and dry as a "yes or no" answer to that question. The selective pressures on organisms can cause them to lose complex organs as well as gain more. We know of many different prokaryotes and many eukaryotes that have not altered radically in millions of years, but, we also know of many macroscale organisms that have stayed pretty much the same for the same time period such as shark species or certain reptiles. I would have to say that whether a pred-prey situation or sexual selective scenario is present really determines whether any one species undergoes a process whereby it eventually gets more and more complex. Many only struggle for resources and simply don't require anything new added to their inventory to keep them abundant.

Just thought I'd add, the R-groups of some amino acids such as valine, alanine, leucine, isoleucine and phenylalanine are purely hydrocarbon based. So they aren't hydrocarbons per se, but do have those primary structures as part of their overall make-up.

[CaptainChewbacca]

oops, did I say permian...


My bad, meant proterozoic. My geology not so good.

In pennace you will do 200 pushups while reciting the geologic timsecale.

Thus speaketh the SDN high inquisitor of geology!

[wilfulton]

According to the wizard in Conan the Barbarian:


"...but you know, success can test one's mettle as surely as the strongest adversary..."

In a way, it is true.

[Darth Fanboy]

How Lowly Bacteria Froze Earth Solid
By Robert Roy Britt
LiveScience Senior Writer
posted: 01 August 2005
02:00 pm ET
"But if it ever happens, all life on Earth would likely be destroyed. We could probably get out only by becoming a runaway greenhouse planet like Venus."

Interesting stuff.

You see! Bush isn't signing Kyoto because he's an idiot! It's to SAVE THE EARTH.