For nearly three-quarters of its history, life on Earth existed solely as a world of single-celled, microscopic organisms. Our modern planet owes its very character to their activities.

The ocean is home to an astronomical abundance of microbes. A single millilitre of surface seawater contains roughly one million living bacteria and other single-celled organisms. Globally, the total oceanic microbial population reaches a staggering 100 octillion living cells – that is

100,000,000,000,000,000,000,000,000,000!

Consequently, the oceans represent the largest living reservoir on Earth.

Single-celled microorganisms occupy an immense diversity of ecological niches. While their functions vary across different ecosystems, they consistently play the leading roles.

We must study microbial life closely, for it is the baseline of all life.

How is the single-celled world structured on our planet? Let’s explore together!