The most enigmatic extreme event

In the last activity we saw how the Earth was formed. But, it was far from the planet we know today.

Some basic conditions needed for habitability on our planet are:

• The distance of Earth from the Sun (Circumstellar habitable zone)
• The presence of liquid water and the ability to support it
• The unique structure of the Earth and plate tectonics (differentiation)

How do these conditions and the events we’ve considered so far relate to development of complex life?

Common ingredients of life

The life we see around us is incredibly diverse and complex. But, there are many commonalities between living organisms that point towards a single origin.

Earlier we considered the importance of elements as the building blocks of everything in the universe. The elements needed for life as we know it are the first commonality.

The element carbon (C) is crucial and has many fascinating chemical properties. Other important elements are:

• Hydrogen (H)
• Oxygen (O)
• Nitrogen (N)
• Sulfur (S)

All of which were created in the first generation of stars. Fascinatingly, the chemical composition of life is actually very close to that of a star. This shows an intimate connection between the processes occurring across the universe and on our planet.

The second commonality is the way life propagates through the evolution of cells, this is shared across all organisms.

Origin of life

The origin of life remains enigmatic. Direct evidence for life is found around 3.5 billion years ago, but it could have emerged several hundreds of millions of years earlier.

There is little direct evidence preserved in the rocks that make up Earth’s crust (geological record) to help us understand the conditions that allowed life to emerge.

Arguably, this is the single most important event in our existence. To the best of our knowledge, it only occurred once in Earth’s history and has affected the way our habitat has formed.

Truly one of the most remarkable and extreme events.

Next we’ll explore some extreme events that helped to bring about more complex life. They were crucial and led to life in its current form.