The Little Things that Change the World

“…the Genesis 8:22 that I use in there is that ‘as long as the earth remains there will be seed time and harvest, cold and heat, winter and summer, day and night,’ my point is, God’s still up there. The arrogance of people to think that we, human beings, would be able to change what He is doing in the climate is to me outrageous.”

– Sen. James Inhofe, 2012

This past winter, once again Sen. Inhofe cited the bible as evidence for the inability of humans to impact the global climate while brandishing a snowball on the floor of the senate.  The true arrogance here is in the position Sen. Inhofe and others have taken denying the extensive evidence science has brought forward in favor of a literal interpretation of an ancient religious text.  To suggest humans are too small to cause such an effect is to ignore the changes in the Earth’s atmosphere throughout geologic time.  The reality is in the data gleaned from the rock record.  Though in some ways we have to give Sen. Inhofe and likeminded people credit for consistency as they also deny the age of the Earth, attributing the vast majority of geologic phenomena to a global flood event taking place less than 10,000 years ago.  This stance makes it particularly difficult to engage with Sen. Inhofe, et al based on the actual evidence science has brought forth.

One can summarize the evidence contained in the rock record for the composition of the atmosphere with charts such as this:

The composition of the atmosphere over time. Image: Nature.com

Looking closely, one notices the amounts of carbon dioxide and oxygen in the atmosphere have varied widely, at times on relatively short time scales of hundreds of thousands, or a few million years.

The history basically goes like this:

  1. The atmosphere of the early Earth had virtually no oxygen.
  2. A little bit of oxygen was formed due to dissociation reactions of water, however the majority of oxygen was produced as a result of early bacteria and archaea “inventing” photosynthesis, probably around 3.5 billion years ago.
    1. Fossil evidence for these organisms include stromatolites.
  3.  The oxygen combined with iron washed into the oceans from landmasses subjected to weathering.
    1. This resulted in the formation of banded iron formations of finely layered magnetite and hematite.  All of the iron our modern technology uses has been mined from these deposits.
  4. The banded iron formations stopped forming about 1.8 billion years ago, when the iron in the oceans was used up.  At this time, lacking available oceanic iron to bind with, the oxygen started to build up in the atmosphere.
  5. The advent of atmospheric oxygen led to the opportunity to bind with a new source of iron: rocks and sediments on the land.
    1. With available oxygen, these iron rich materials essentially rusted, turning the reddish hues we all recognize.  The result was a thick sequence of what are called red beds, sedimentary rocks with a distinct reddish hue.  No red beds are found older than 2 billion years.
    2. Besides the thick sequence of preCambrian red beds, another prominent set was formed during the Triassic Period.
  6. Another potential impact of the increased levels of oxygen in the atmosphere is the onset of worldwide glaciation events lasting for perhaps tens if not hundreds of millions of years, the so called “snowball Earth.”
    1. The increased level of oxygen would have reacted with the potent greenhouse gas methane prevalent in the early atmosphere to produce the less effective carbon dioxide.  This led to a rapid cooling which resulted in extensive ice sheets in low latitudes far from the poles.

The remarkable thing is this all came about because some single-celled organisms developed the ability to photosynthesize!  And the impact on Earth’s atmosphere and climate were far greater than the changes of current times brought about through the activities of a large group of multi-cellular organisms we call humans.  Amazing what adding a bit of oxygen does to the overall Earth System.  Perhaps future geologists will discover in our fossilized edifices the evidence for large scale climate change, much as contemporary scientists found a clue for past changes in ancient stromatolites.

In future posts, we take up the case of a great depletion of carbon dioxide in the mid-Paleozoic, as well as considerations for educators.

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