Our universe exists on an incomprehensible scale; a supposedly infinite darkness, punctuated
with at least 70 sextillion stars shining their light through the cosmos. There are
more stars out there than there are grains of sand on every beach on Earth, it would
be impossible to truly comprehend the immense size of our universe. And yet planets like
ours appear to be rare, even on this scale.
A speck of blue in the infinite abyss, we are unique in the solar system. There is one
phenomenon found here that we have yet to find anywhere else in the observable universe.
Life. The product of chemistry and biology, and one of the true great marvels of existence.
Risen from the primordial soup in the early years of our planet, life forged a path through
the ages; driven by the need to survive, and the will to evolve, it changed. Adapted. Crawled
from turbulent waters to conquer land and sky, giving rise to empires and dynasties.
3.5 billion years of evolution, with every step written in the rocks beneath our feet,
the steps that lead towards the rise of humanity.
But life on earth had humble beginnings.
It is midnight on the geological clock. Present day, and a familiar scene is playing out.
We are currently living through the Anthropocene era, the most recent period in Earth's history.
It began when human activity started to have a significant impact on the planet's climate
and ecosystems.
Within this era, which may have only begun somewhere in the mid-20th century, we have
already left our mark on the planet.
Cities have risen from nature’s great wilderness since humanity’s dawn, ravaging ecosystems
and habitats without regard for the life that inhabits them. 1 million species are now at
risk of extinction, and 36.2 gigatonnes of carbon dioxide emissions are given out each
year from fossil fuels and industry.
And all of this, has taken place in only the last two seconds on the geological timescale.
To see where it all began, we need to turn back the clock, by 4.5 billion years.
It's 12:00 Am when the Earth begins to form from the solar nebula. Small particles come
together, bound by the force of gravity, into larger particles. Earth's rocky core forms
first, with heavy elements colliding together. Dense material sinks to the centre, while
the lighter material creates the planet’s crust. The magnetic field forms, and Earth’s
gravity captures some of the gases that make up the early atmosphere.
Several hours pass on the geological clock, as the planet cools from a molten state.
Over immense periods of time, our primitive oceans formed. Water could only exist as a
gas until the Earth finally cooled below 100 degrees celcius. At this time, about 3.8
billion years ago, the water condensed into rain which fell upon our rocky planet, filling
up the basins that are now our oceans.
More than 4 billion years ago, the young Earth had developed conditions that allowed the
generation of the basic building blocks of life: nucleic acids, amino acids, and lipids.
These macromolecules gave rise to prototype cells that would led to the earliest life
forms.
The cradle of life that nurtured these early organisms was no Garden of Eden; it was a
magma-bleeding abyss where no light from the sun could reach; the deep sea vents, where
the Last Universal Common Ancestor gave rise to two domains of life. The Archaea and Bacteria.
These organisms thrived in an anaerobic world, for there was no oxygen in the early atmosphere.
It wasn’t until around 2.5 billion years ago, when cyanobacteria first evolved. Photosynthetic
organisms, which began the vital task of converting carbon dioxide into oxygen.
By 6:00 on our 12 hour geological clock, the atmosphere was oxygen rich. A vital step in
earth’s history, which would enable complex life to evolve further down the line.
The next crucial chapter occurred 2 billion years ago. Two microbes, drifting in the deep
sea vents, had a unique interaction.
One was an archaeon, and the other a bacterium. One devoured the other, and the two became
one, giving rise to the last domain of life. Eukaryotes. The first life forms to contain
genetic material as DNA in the form of chromosomes, contained within a distinct nucleus.
This interaction created the progenitor of all fungi, plants and animals, as the swallowed
bacterium evolved into the power-generating mitochondria, which all eukaryotic life forms
depend on.
For most of the Earth’s history, the planet was dominated by only single-celled life,
drifting in the oceans. This was the Proterozoic period, a time which lasted for nearly 2 billion
years, during which life existed only in simple forms.
And as this period came to an end, the cell did something spectacular. A new era dawned
upon Earth, one that would catalyse and revolutionise the game of evolution. The Cambrian Explosion.
The diversification and evolution that arose from the Cambrian Explosion was so great,
that life began evolving in new and incredible ways. This laid the foundations of the three
great Eras that would follow on Planet Earth, the Paleozoic, Mesozoic and Cenozoic, the
next chapters in the story of life.