Life Before Oxygen


The gringa would like to share an interesting timeline of the earliest Earth events. Now, ancient history might seem boring but the gringa discovered a very peculiar fact she had never thought about before. There was life on Earth before there was even oxygen! How in the world is that possible? Well, think about it. In order for biological life as we know it to exist on Earth, oxygen must be the second most plentiful  gas in the atmosphere.  In general, the air we breathe is about:

  • 78% Nitrogen
  • 21% Oxygen
  • Less than 1% Argon
  • Less than 1% Carbon Dioxide

To create this winning oxygenated atmospheric recipe on ancient Earth, trees had to be photosynthesizing. But there was stuff living here long before there were trees! How the heck did it survive? Well, let’s look at the timeline first:

  • 4.5 billion years ago (or thereabouts) Earth comes into existence
  • 3.5 billion years ago (or thereabouts) microbes are living on Earth
  • 2.5 billion years ago (or thereabouts) sulfur-eating bacteria is living on Earth
  • 530 million years ago (or thereabouts) fish are living on Earth
  • 400 million years ago (or thereabouts) trees emerged on Earth
  • 230 million years ago (or thereabouts) dinosaurs are living on Earth

So, the gringa wants to know how the heck microbes, bacteria and fish were surviving on an Earth that had, compared to today’s atmospheric standards, a virtually zero oxygen environment. Scientists believe that early Earth’s atmosphere consisted of methane, carbon monoxide, hydrogen sulfide and ammonia.  Earth’s earliest microbes lived in the sediments below the shallows of the planet’s oceans shorelines. They fed and breathed on the sulfur in the atmosphere.  As they absorbed sunlight for energy, they became the first life form to contribute oxygen to the atmosphere through the process of photosynthesis. But shoreline colonies of microbes could by no means contribute oxygen on the same level as vast forests. So oxygen was basically a trace atmospheric gas at this time.

Ancient bacteria ate sulfur and converted hydrogen sulfide into sulfate, which is oxidized sulfur.  Cyanobacteria, commonly called blue-green algae, began to proliferate and also performed a photosynthesis function adding oxygen to the planet’s oceans and atmosphere.

As microbes and bacteria died, they received a burial at sea. Their decomposition also contributed more oxygen to the waters. As the world’s oceans began to become more oxygenated, fish started making their appearance during the Cambrian era. They were typically invertebrate species like jellyfish, worms, crustaceans and molluscs.

Jellyfish diffuse oxygen through their cells. Giant tube worms, that still live in our oceans near underwater volcanic vents, an inhospitable environment for most carbon based life, have a special organ to convert carbon dioxide and hydrogen sulfide into oxygen. Today’s molluscs have a respiratory system that uses gills, just like fish.

And from these strange beginnings, it has been a slow evolutionary crawl to the world we know today. The gringa is amazed. We all owe our lives to the humble microbe and smelly sulfur. Fascinating. But where did microbes come from? Did they simply just “appear” out of thin air? Could they have originated from another planet, arriving here by accident or delivered on purpose by ancestral aliens? Let’s look at planets that had similar atmosphere’s to early Earth, which would have then naturally been a likely choice for microbes looking for a new home:

  • Venus has an atmosphere enveloped by sulfuric clouds.
  • Jupiter, Saturn, Uranus & Neptune all have methane and ammonia in their atmospheres, as does Saturn’s moon, Titan
  • Pluto has an atmosphere dominated by carbon monoxide
  • The atmosphere of Mars is 96% carbon dioxide but also has ammonia and hydrogen sulfide

So, the gringa thinks it’s possible that the ancestral microbes we humans evolved from may have originated from outer space. But, over time, a life form evolved that can never naturally survive on the planet of its origins. So much for a homecoming party!

Sources:

www.livescience.com/earliest fossils

www.space.com

forestry.about.com

www.livescience.com/dinosaurs

www.astrobio.net/early atmosphere

www.astrobio.net/oxygen

www2.astro.psu.edu

www.reference.com

www.seasky.org

mollusks.weebly.com

Image Credit:  riaus.tv

 

 

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