How Oxygen Shaped Life on Planet Earth

By Shlomo Maital    

Earth – 4 billion years ago — not the “blue marble” yet!

    To shape life on Earth, as we know it today, a great many imporbable things had to happen, and coincide. One of them was – the creation of oxygen.  How did that happen?  A new article in Nature Ecology and Evolution, by Weizmann Intitute Professor Dan Tawfik and student Jagoda Yablonski, suggests how this happened.  The article is summarized by the excellent Haaretz science writer Asaf Ronal:

  In the first half of her life so far, our bluish planet looked completely different. The sky and sea were filled with ammonia and iron sulfur compounds, and painted in a murky heat (and the smell was accordingly). 2.4 billion years ago, the Earth underwent a geochemical image revolution: the atmosphere filled with oxygen, the reddish-brown compounds oxidized and sank to the bottom and the sky and oceans became clearer and got the blue color we know.

    This event is called the “Great Oxidation.” The radical change in the Earth’s environment is considered one of the key events in the evolution of life on the planet because without oxygen-filled air, the complex animals that rely on breathing air for energy production could not have evolved. The explanation for the sharp rise in oxygen concentration lies in the development of the ability of organisms to do oxidative photosynthesis – to produce energy from sunlight in a process that produces oxygen.

But how did this happens?

     However, the question of when this ability for oxidative photosynthesis appeared in Earth’s history, and the exact process that led to the environmental upheaval, has remained scientifically controversial. Now, a new study uses the tools of evolutionary and genetic research to date the emergence of oxidative photosynthesis to a period of about 3.1 billion years ago. The study was published yesterday (Thursday) in the scientific journal Nature Ecology & Evolution, and points to the possibility that those organisms with the new capacity created and expanded pockets of oxygen-rich environment 700 million years later, until the amount of oxygen reached the critical mass required to fundamentally change the chemical environment of the entire planet’s surface.

    Recently, NASA landed the Perseverence explorer on Mars.  One goal is to search for life there.  But some scientists think there may be life elsewhere in the cosmos – on Titan, the moon of Saturn.  It is the only moon known to have a dense atmosphere…and deep lakes.  But the lakes are not water – they are liquid methane and ethane, and Titan is incredibly cold, so the ice that does exist is frozen solid.

   If life on Earth evolved on the basis of oxygen – could there be life on Titan, on the basis of methane?  Why not?   Why could not cells adapt to using methane, rather than oxygen?

    One day, we will know.