WE MAY owe our green Earth to a big freeze that covered the entire planet in thick sheets of ice 2.3 billion years ago. As this “snowball” Earth thawed, it released strong oxidants into the oceans and atmosphere for the first time, setting off the chain of events that led to oxygen-tolerant marine organisms and photosynthesis as we know it today.
The evolution of efficient, oxygen-based photosynthesis has been hard to explain. Primitive forms gathered energy from light by using it to free electrons from sulphur and iron in an oxygen-free environment. Oxygenic photosynthesis, which involves freeing electrons from water,…
