Friday, October 1, 2010

Ecological Disaster - a Third of a Billion Years Ago

"How Plants Drove First Animals Onto Land"
Wired Science (September 29, 2010)

"About 350 million years ago, evolution took one small step for fish, and a giant leap for every terrestrial animal since. According to a new study, it was all made possible by plants.

"Prehistoric oxygen levels extrapolated from ancient mineral sediments suggest aquatic life went into overdrive after plants boosted atmospheric oxygen levels. Oceans became so fiercely competitive that some fish sought safe haven outside them.

"Some scientists have proposed as much, but the new research, published Sept. 28 in the Proceedings of the National Academy of Sciences, provides the first solid evidence.

" 'Before this paper, there was essentially no experimental evidence for how oxygen accumulated through animal history. It was only predicted by theory,' said Tais Dahl, an evolutionary biologist at the University of Southern Denmark’s Nordic Center for Earth Evolution...."

The research involves seafloor samples, molybdenum, and what we've learned about how that relatively-common element, erosion, and how long it takes the average particle to settle to the bottom of the ocean and stay there (about 1,000,000 years).

The Wired Science article tells about one debate in the scientific community - an example of what the Lemming has noticed in other sciences, ranging from biology to geology. It seems that there are two basic philosophies about how development happens:
  • One is that development is gradual, like the smooth growth curve you get when you take data from thousands of people and come up with an "average" person.
    • Growth spurts? Those can't happen - that smoothed-out statistical curve don't have no growth spurts.
      • That's another topic.
  • The other is that development comes in fits and spurts.
    • The sort of thing we see when we look at data from individual human beings.
The advantage of the 'gradualist' philosophy, as the Lemming sees it, is that it allows textbooks to display nice, smooth growth curves; and provides a feeling of continuity.

The advantage of the 'spurt' philosophy, again from the Lemming's point of view, is that it seems to be a somewhat better match with reality. Particularly when researchers start collecting enough data - and track specific instances of a process, rather than averages from a set of instances.

Back to that article:

"...The first, traditional view holds that planetary oxygen levels continued to rise steadily, reaching near-contemporary levels well before Earth’s life diversified again, some 400 million years ago. In this narrative, it was only a matter of time - another 50 million years, give or take - before a few lagoon-dwelling creatures ventured onto land. Terrestrial life was a clockwork eventuality. Plants provided more oxygen, but weren’t essential.

"According to the other interpretation, oxygen levels stayed steady from 550 million to 400 million years ago, when the forerunners of modern plants evolved and flourished. Only then did oxygen jump, allowing fish - until then a small, relatively insignificant part of the animal kingdom - to take large, highly predatory forms...."

In this case, "large" means up to 30 feet long - which would be a substantial fish even today, about a third of a billion years down the pike.

Oxygen: Not Necessary for Life-As-We-Know-It

We're used to living in an atmosphere with quite a great deal of oxygen in it. In fact, human beings need oxygen to survive. So to quite a few other creatures.

Not all, though. (April 9, 2010)

As the Wired Science article points out, the amount of oxygen in Earth's atmosphere has changed - quite a lot - since plants started dumping that highly reactive gas into the environment.

We're the sort of creature that's geared to use oxygen's habit of reacting with a wide range of substances - releasing quite a lot of energy in the process. We need the stuff. Other critters can be killed by exposing them to oxygen. ("Anaerobic bacteria culture," Encyclopedia of Surgery)

From what we've learned about Earth, about a third of a billion to half a billion years back, it looks photosynthetic plants triggered a massive ecological disaster. Their metabolism dumped oxygen into the ocean and atmosphere - killing off species which couldn't cope with that reactive gas.

Finally, the Wired Science article has some cool pictures: of a 30-foot-long fish (that used oxygen), a - thing - that could live on water or land, and leaves from the gingko tree - that hasn't changed much in the last 350,000,000 years.

Related posts:More related posts, at

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