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Gabrielle Walker unearths the evidence of our evolutionary past
Wednesdays 18 and 25 May and 1 June 2005 9.00-9.30pm 

In the second series of An Earth Made for Life Gabrielle Walker continues her quest to understand why complex life is found on our planet, but not on any of our celestial neighbours. From the outback of Australia to the walls of the Grand Canyon Gabrielle unearths evidence of the dramatic changes that took place on our planet billions of years ago which may have triggered the rise of animals.

Gabrielle Walker and Mike Timmons
Mike Timmons of the New Mexico Bureau of Geology & Mineral Resources explains to Gabrielle how the Grand Canyon formed part of the world's oldest known super-continent, Rodinia

Programme 1 - Shifting Continents

Rocks in South Africa show that life was firmly established on Earth two and half billion years ago.

They contain fossilised microbial mats - evidence of our slimy ancestors.

Two billion years later the Earth was swimming with complex animals. But what caused the change?

The rocks of the Grand Canyon tell us that super-continents - huge aggregations of smaller continents - were forming and ripping apart.

A result of these intense events was a series of climatic flip flops that ended with what is now known as the Snowball Earths.

The theory goes that these catastrophic periods of time - when the entire planet is gripped by ice - may have shocked the simple earthlings and spawned life as we know it.

Listen again Listen again to Programme 1
Gabrielle Walker visits the world's largest iron mine in Australia
Gabrielle surveys the world's largest iron mine, in Australia, which holds clues to the greatest mass poisoning in history

Programme 2 - Mass Poisoning

At the same time as the continents were shifting across the planet's surface the Earth's atmosphere was undergoing a tremendous change.

In what has been described as the 'greatest mass poisoning in history', oxygen started to build up for the first time.

The gas we now all breathe today was noxious to most organisms, but high-octane rocket fuel to our microbial ancestors.

It shocked our sedentary ancestors out of their sessile lifestyles and allowed them to pursue more active lifestyles.

The evidence of this cataclysmic change is to be seen in great iron mines in Australia, made when iron dissolved in the oceans reacted with the new oxygen and rusted out to the seafloor.

Listen again Listen again to Programme 2
Gabrielle Walker and Prof. Martin Brasier
Martin Brasier of Oxford University shows Gabrielle the Ediacaran Fossils found in Charnwood Forest, Leicestershire

Programme 3 - Sex, Death and War

To take advantage of the new conditions on Earth, life had to find a way to accelerate evolution.  The solution was sex.

And if tiny fossils from an arctic island are to be believed, sex has been with us for 1200 million years.

The fossils - coyly called Bangiomorpha pubescens - are also the oldest multicellular form of life.

It was not for another 700 million years that we see evidence for the first massive radiation of animals, however.

This event - known as the Cambrian Explosion - paved the way for modern creatures. But what was its cause?

One suggestion is war: as predators found a better way to kill, so prey found new ways to survive. 

In doing so, life took on a wholly new role in managing the environment and ultimately paved the way for humanity.

Listen again Listen again to Programme 3

Click here to find out about the first series of An Earth Made for Life, broadcast in 2003.
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