Sunday, February 14, 2016

{6} Evolution of Earth's Atmosphere - easy version

My last evolution post, {5b} Earth's Earliest Climate - By Angela Hessler, was fairly weighty stuff, so I'm going to lighten it up a bit in this installment.  First, I have an excellent 5 minute video that though being a cartoon, is the best short summary of our four and a half billion journey I've been able to find on YouTube.  For the intermission I link to Michael Marshall's wonderfully concise list of nearly 70 milestone events along Earth's fantastic evolutionary pageant. 

From there we'll consider our Moon's profound influence on Earth's evolution with another short YouTube video.  Then it's back to school work with the course outline of a University of Michigan's Global Change Courses, section: "Evolution Of The Atmosphere: Composition, Structure And Energy"


History of Earth and the Early Atmosphere

shazmosushi |  5:33

Published on Dec 8, 2013
Short animation covering 4.5 billion years. The animation was download from Unit #4 of The Big History Project.  Checkout the 18 minute introduction video of the project -- available here:

Michael Marshall put together a concise listing of nearly 70 important evolutionary milestone over at along with links that lead to further details.  It's done with clarity and make a perfect quick reference.

Timeline: The evolution of life

By Michael Marshall  |  DAILY NEWS  |  July 14, 2009  


Did the Moon Create Life on Earth?

Science Channel  |  3:26 min

Published on Aug 19, 2015
Without the strong pull of the moon, 
would there have been the massive tidal pools that were the perfect mixing bowl for life?
{not to mention all the rock crushing, pulverizing, mixing and redistribution}

Catch new episodes of HOW THE UNIVERSE WORKS Tuesdays at 10/9c on Science!

The University of Michigan's Global Change Courses, part of the Program in the Environment, offer a modern approach to undergraduate science and social science education.  In interdisciplinary courses the topic of Global Change from physical and human perspectives are examined, and case studies are used to explore scenarios for sustainability. Small, GSI-led group sessions promote critical thinking and analysis. 
The courses are aimed at first and second year students who want to understand the historical and modern aspects of Global Change and Sustainability.  These 4-credit courses include laboratory sections and carry distribution credit.
Evolution Of The Atmosphere: 
      Composition, Structure And Energy

Driving Questions:
  • How did the atmosphere evolve into what it is today?
  • What gases in the atmosphere are important to life and how are they maintained?
  • What natural variations occur in atmospheric constituents and what are the important time scales for change? 
1. The Earliest Atmosphere, Oceans, and Continents
     Oxygen in the Atmosphere
     Early Oceans
     Early Continents

2. Evolution of the Present Atmosphere
The evolution of the atmosphere could be divided into four separate stages:
  1. Origin
  2. Chemical/ pre-biological era
  3. Microbial era, and
  4. Biological era.

The Biological Era - The Formation of Atmospheric Oxygen

Firstly, Eukaryotic metabolism could only have begun once the level of oxygen had built up to about 0.2%, or ~1% of its present abundance. This must have occurred by ~2 billion years ago, according to the fossil record. Thus, the eukaryotes came about as a consequence of the long, steady, but less efficient earlier photosynthesis carried out by Prokaryotes.

Oxygen increased in stages, first through photolysis (Figure 1) of water vapor and carbon dioxide by ultraviolet energy and, possibly, lightning:
H2O -> H + OH
produces a hydroxyl radical (OH) and
CO2 -> CO+ O
produces an atomic oxygen (O). The OH is very reactive and combines with the O
O + OH -> O2 + H

The hydrogen atoms formed in these reactions are light and some small fraction escape to space allowing the O2 to build to a very low concentration, probably yielded only about 1% of the oxygen available today.

Secondly, once sufficient oxygen had accumulated in the stratosphere, it was acted on by sunlight to form ozone, which allowed colonization of the land. The first evidence for vascular plant colonization of the land dates back to ~400 million years ago.

Thirdly, the availability of oxygen enabled a diversification of metabolic pathways, leading to a great increase in efficiency. The bulk of the oxygen formed once life began on the planet, principally through the process of photosynthesis:

6CO2 + 6H2O <--> C6H12O6 + 6O2
where carbon dioxide and water vapor, in the presence of light, produce organics and oxygen. The reaction can go either way as in the case of respiration or decay the organic matter takes up oxygen to form carbon dioxide and water vapor.

Life started to have a major impact on the environment once photosynthetic organisms evolved.
     Banded Iron Formations
     Red Beds
     The Oxygen Concentration Problem.
     The Early Ultraviolet Problem
     Fluctuations in Oxygen    

3. Composition of the Present Atmosphere
        Comparison to Other Planets
        Current Composition
        Greenhouse Gases

Radiative Properties

Sources and Sinks
Greenhouse Gases (apart from water vapor) include:
  • Carbon Dioxide
  • Chlorofluorocarbons (CFCs)
  • Methane
  • Nitrous Oxide
  • Ozone
and each have different sources (emission mechanisms) and sinks (removal mechanisms) as outlined below.

4. Summary
We developed a few useful tools for the study of biogeochemical cycles. These include the concepts of the reservoir, fluxes, and equilibria.
  • Atmospheric evolution progressed in four stages, leading to the current situation. The atmosphere has not always been as it is today - and it will change again in the future. It is closely controlled by life and, in turn, controls life processes. Complex feedback mechanisms are at play that we do not yet understand. 
  • Oxygen became a key atmospheric constituent due entirely to life processes. It built up slowly over time, first oxidizing materials in the oceans and then on land. The current level (20%) is maintained by processes not yet understood. 
  • Sometime just before the Cambrian, atmospheric oxygen reached levels close enough to today's to allow for the rapid evolution of the higher life forms. For the rest of geologic time, the oxygen in the atmosphere has been maintained by the photosynthesis of the green plants of the world, much of it by green algae in the surface waters of the ocean.
  • Selective absorbers in our atmosphere keep the surface of the earth warmer than they would be without an atmosphere.

Wednesday, January 6, 2016
{1} Our Global Heat and Moisture Distribution Engine

Saturday, January 9, 2016
{2} Co-evolution of Minerals and Life | Dr Robert Hazen

Thursday, January 14, 2016
{3} Evolution of Carbon and our biosphere - Professor Hazen focuses on the element Carbon

Saturday, January 23, 2016
{4} Evolution-Considering Deep Time and a Couple Big Breaks

Saturday, February 6, 2016
{5a} The Most Beautiful Graph on Earth - A. Hessler

Sunday, February 7, 2016
{5b} Earth's Earliest Climate - By Angela Hessler

Sunday, February 14, 2016
{6} Evolution of Earth's Atmosphere - easy version

Thursday, February 18, 2016
{7} Our Global Heat and Moisture Distribution Engine, visualized

Friday, February 19, 2016
{8} Atmospheric Insulation Explained - appreciating our climate engine

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