Re: Snowball earth on Channel 4
- From: "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx>
- Date: Wed, 10 Dec 2008 13:16:12 -0500 (EST)
"Anthony Campbell" <ac@xxxxxxxxxxxxxxxx> wrote in message news:ghjkr5$1a6n$1@xxxxxxxxxxxxxxxxxxxxxx
Channel 4 TV in Britain is currently broadcasting a series on
catastrophes that are supposed to have affected evolution. Last week we
had Snowball Earth -- the hypothesis that the earth was completely
covered by glaciers some 600 million years ago. This was presented as if
if it were established scientific orthodoxy -- no mention of any
dissenting views.
The presenter, Tony Robinson, came out with the rather surprising
statement that atmospheric oxygen had been produced by this event. As
far as I know the current orthodox view is still that it was produced by
photosynthesis due to cyanobacteria. How serious is the alternative
hypothesis?
A cyanobacterium produces oxygen all its life. And then it dies. And
its biomass decays and is oxidized. And all that oxygen that had
been produced during the life of that organism is converted back to
CO2.
So at the very least, it is a gross oversimplification to say that atmospheric
oxygen came from photosynthesis. A less gross simplification would be
that oxygen comes from photosynthesis plus biomass burial. You need
them both. You also need to have nothing in the hydrosphere or
geosphere (H2S? Fe++?) that would tend to soak up the oxygen as
fast as it is produced.
So what does this have to do with the "Snowball" event? Well, all the
evidence suggests that cyanobacteria had been practicing photosynthesis
for over a billion years by that time, yet they had not yet succeeded in
putting significant quantities of oxygen in the air. Then, in a short period
of time - right at the same time as the hypothetical Snowball, the oxygen
level in the atmosphere jumped to close to modern levels.
So we have a clear "post hoc" and a lot of geologists think they understand
the mechanism giving us a "propter hoc"
.
- References:
- Snowball earth on Channel 4
- From: Anthony Campbell
- Snowball earth on Channel 4
- Prev by Date: Snowball earth on Channel 4
- Next by Date: Call for Papers: The 2009 International Conference on Modeling,
- Previous by thread: Snowball earth on Channel 4
- Next by thread: Call for Papers: The 2009 International Conference on Modeling,
- Index(es):
Relevant Pages
|
