Earth’s Earliest Atmosphere: Cyanobacteria

We owe a huge nod of gratitude to the wee photosynthetic microbes known as cyanobacteria for their work in helping to create the first oxygen to enter our atmosphere and make you and I — & indeed all life on Earth — possible.

When the Earth formed 4.5 billion years ago, it was an inhospitable place. Even with a Sun some 25 per cent weaker than it is today, ours was a molten world that needed to undergo a long period of cooling before the conditions for life would arise.

And arise they did. On the planet's surface, volcanoes spewed lava and volatile gasses into what would become our earliest atmosphere.

It looked very different from the one we know today — nitrogen, carbon dioxide, ammonia, methane and small amounts of water vapour made up the gassy soup surrounding our world.

But that first water would change everything. As the water vapour condensed, it came back to the surface bit by bit. Over a very long period of time, those waters pooled and gathered and became our first oceans. It was in this early ocean some 2.7 billion years ago that cyanobacteria, or blue-green algae, wonderous photosynthetic microbes, would take up that weakened sunlight and water vapour to process the carbon dioxide from the atmosphere, producing other chemical compounds and oxygen as a by-product.