The Naked Scientists

The Naked Scientists Forum

Author Topic: The change in Earth's oxygen levels  (Read 4662 times)

Online chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
The change in Earth's oxygen levels
« on: 14/12/2006 04:12:25 »
Here's a question I've been pondering and would appreciate your thoughts on:

"Oxygen now makes up about 20% of the atmosphere, but historically, when the dinosaurs roamed the planet, that number was 35% or thereabouts. Where has that oxygen gone and what's provoked that drop?"

Chris


 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Re: The change in Earth's oxygen levels
« Reply #1 on: 15/12/2006 00:24:00 »
Dear Doctor,
 I have a pain in my ----- that is another subject, though.

For most ups and down of the oxygen content of the atmosphere over time algae, and to a much lesser extent, other plants, are quite often referred to as the culprit. Population levels fluctuate, yada, yada, yada.

Then, another theory states that the output of sulfur from volcanic activity combines with atmospheric oxygen to form acid rain causes oxygen depletion.

Both are minor, although the sulfur is a possibility for the Permian extinction, a period of more intense vulcanism since over 700,000,000 years ago.

BUT Consider this: Water enters the earth's atmosphere by way of icy meteorites. This water amounts to a rise in sea level of 1" every 20,000 years. The numbers just do not work out for the variations observed in isotopic oxygen trapped in rocks.

The Culprit; CaCO3, limestone rocks. The more limestone formed the less the oxygen content of the atmosphere. It is a direct relation in the geologic record. And the number of mega-tonnes work out.

A verbose answer for a simple question. But give me a break, I've been sick and pitiful. I need attention. (whine, whine)  [xx(]
 
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: The change in Earth's oxygen levels
« Reply #2 on: 15/12/2006 00:45:03 »
I think the levels of 35% were in the carboniferous, they are definitely basing some of it on the size of flying insects. As this is a period relating to huge amounts of coal and limestone being layed down I guess these were getting rid of it, although to sustain for very long I would have thought there would have to be a lot of CO2 being released volcanically. I guess the earth quietened down a bit geologically since then.
 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Re: The change in Earth's oxygen levels
« Reply #3 on: 15/12/2006 03:53:49 »
ERRATA

Above last post by me - Not only CaCO3 but any carbon fixing bacteria or organizm - bacteria being the most numerous and 50% + of this fixed as limestone.

 

The Naked Scientists Forum

Re: The change in Earth's oxygen levels
« Reply #3 on: 15/12/2006 03:53:49 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums