It’s pretty well accepted among the scientific community that life existed as far back as 3.5 billion years ago. But those were days before oxygen had accumulated to significant levels.What kind of creatures were lurking an an oxygen-free world?...
Whiffs of oxygen
It’s pretty well accepted among the scientific community that life existed
as far back as 3.5 billion years ago. But those were days before oxygen
had accumulated to significant levels.What kind of creatures were
lurking an an oxygen-free world?
It wasn’t until 2.4 billion years ago during the so-called Great Oxidation Event
that photosynthesizing cyanobacteria (blue-green algae) produced enough
oxygen to saturate into organic matter and dissolved iron in the ocean
and then more. The free oxygen built up in the atmosphere, killing off
a huge number of these anaerobic inhabitants and making room for new
species of oxygen-dependent organisms to take over. This period brought
on one of the most important changes in the evolutionary history of
life. was a major step in the evolution of life on Earth.
But can Earth’s history be so neatly divided into a world before and after oxygen? In a paper published in the journal Nature Geoscience
this month, NASA astrobiology researcher Andrew Czaja writes that
“whiffs of oxygen” may have been present long before the
Great Oxidation Event and would match up with some early oxygen
dependent fossils from long ago.
Take for example a kind of manganese-reducing bacteria that might have
been present nearly 3 billion years ago. To do its work, it required
free oxygen to oxidize manganese. Could there have been a “local
oxygen oasis”? Or were there “global oxygen pulses”?
Czaja says that oxygen couldn’t have been widespread at this
point because even shallow surface waters were demonstrably anoxic just
200 million years later.
How do you have an Ice Age and warming at the same time? As wacky as
the climate patterns on Earth are right now, they’ve been
stranger in human history.
A bipolar seesaw
A paper in the journal Nature this week draws attention to the Younger Dryas conundrum about 13,000 years ago, a period of abrupt climate change. The last Ice Age was ending, owing to a shift in the Earth’s orientation to the Sun,
bringing us into the modern, temperate period that sustained the rise
of civilizations. But the global warming of then was pretty a bumpy
ride. There was simultaneous warming and cooling on the planet at the
same time.
A cold blast hit northern Europe and froze it again for another
thousand years. Meanwhile, the polar South continued heating up and
glaciers retreated. The Younger Dryas, named after a white flower that
grows in the Arctic, was not a global event.
The research, undertaken by Columbia University’s Lamon-Doherty
Earth Observatory, tracked the retreat of a New Zealand glacier by
examining the exposed rocks, called moraines. “Whereas North
Atlantic mean annual temperatures dropped drastically, by at least
15 °C, atmospheric temperatures in the southern mid
latitudes increased during this period,” the researchers write.
They go on to say that a classic explanation for the variance is the
“bipolar seesaw mechanism,” essentially the shut-off of the
Atlantic Gulf
Stream that brought colder temperatures to the North and heat retention
in the South. Another possible cause is a shift in the intertropical
convergence zone and westerly wind patterns southwards, “which
has been shown to increase Southern Ocean upwelling and outgassing of CO2 abruptly.”
The answer remains elusive whether rising CO2 levels
alone could have caused the South to warm, or whether it needed another
mechanism to move it forward, like the the bipolar seesaw.
Whatever happened, it’s a lesson that global warming is never the same everywhere.