NARRATOR: The first living
organisms appeared on Earth at least 3.5 billion
years ago. To us they would have seemed
tiny and insignificant, yet they were extraordinarily
complex compared to anything else
that had ever existed. Over the next 3.5 billion years
they would diversify and evolve. About 600 million years ago,
some started to combine. Over time, they formed
multicellular organisms like trees, mushrooms,
frogs, dinosaurs, or even the first small mammals,
which probably looked a bit like mice. When the dinosaurs
were wiped out by an asteroid, mammals prospered, evolving into a great range
of new species. One group lived
in trees and ate fruit. They had hands,
stereoscopic vision and unusually large brains. These were our
ancestors, the primates. Our own species, Homo sapiens,
evolved about 200,000 years ago. Now, we treat the
appearance of humans as a new threshold
because we would eventually create entirely new
forms of complexity. Today, we have become
the most important force for change on
the Earth's surface. We are the first species
in 3.5 billion years that has had such power. What makes us so different? For this threshold,
powerful brains are one ingredient, but it's not just
a matter of brains. Many other brainy
species exist. They include dolphins
and chimpanzees and crows. The other critical ingredient
was the development of symbolic language. This enabled humans
to share their ideas with each other
very efficiently. Human communities
grew and interacted, creating the perfect
conditions for something new, the ability
to learn collectively instead of just as individuals. Ideas and knowledge accumulated
generation after generation, and human technologies became
more and more powerful. As knowledge
accumulated over time, our control of resources
and the environment increased and accelerated,
leading humans towards two new thresholds
that would have a huge impact on our planet.