- [Narrator] Earth, the only planet known to maintain life.
A product of scientific phenomena and sheer chance.
This blue speck in space holds the past,
present, and future, of our very existence.
Approximately 4.5 billion years ago,
the Earth formed from particles left over
from the creation of our sun.
Gravity drew these particles together
to form pebbles which then formed boulders,
and eventually, the Earth.
At its heart is a solid inner core
covered by a liquid outer core.
Above this sits the mantle, made of flowing silicate rocks,
and a rocky crust.
This rocky mass is the third planet from the sun,
orbiting the star from an average distance
of about 93 million miles.
It's close enough to the sun to be warm
unlike the cold gas giants.
But not so close that its surface
is exposed to extreme heat and solar radiation
as is the case with Mercury.
Earth's unique position in the solar system
allows it to house phenomena
yet to be found anywhere else in the universe,
particularly liquid surface water and life.
According to one theory, much of Earth's water
is as old as its rocks, both of which having formed
during the Earth's earliest days.
Because of Earth's unique distance from the sun,
the planet is able to contain water
in all of its forms, liquid, ice and gas
rather than have them permanently frozen
or evaporated into space.
But Earth is the only known place in the universe
with liquid water on the surface,
thereby having unique cascading effects on the planet.
It hydrates the land helping create nutrient rich soil.
It collects and pools to form oceans and freshwater systems.
And it cycles upward to add moisture
to Earth's protective atmosphere.
And where there is liquid water, there is life.
About 3.8 billion years ago in Earth's oceans
primitive life existed in the form of microbial organisms.
They and the ensuing billions of years
gave rise to a range of more advanced life forms
that survived in Earth's seas, lands and skies.
As the only world known to harbor life,
Earth's biodiversity is expansive in nature.
An estimated 1.5 million species of plants,
animals, bacteria, fungi and others
have been cataloged with potentially millions,
if not billions more yet to be discovered.
Home to life and fueled by water,
Earth houses a unique global ecosystem
as curious and as grand as the astronomical events
that made them possible.