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- Australian scientists have pinpointed the time when an
Earth-changing form of life appeared - the bacteria which gave us the oxygen
we breathe.
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- Writing in the journal Nature, a team from the Australian
Geological Survey have identified chemical fossils of cyanobacteria in
ancient rocks. It demonstrates that 2.5 billion years ago they were already
changing the face of our planet.
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- It was the emergence of this type of bacteria, able to
use sunlight to produce energy and also oxygen, that turned the sky blue.
In a real sense, the Earth's blue sky has been coloured by life.
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- Before the cyanobacteria evolved the Earth was a very
different place from the world we know today.
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- Several billion years ago the Earth's atmosphere was
made of hydrogen, carbon monoxide and possibly methane, gasses that are
highly toxic to most lifeforms today.
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- It is difficult for us to imagine what the Earth was
like three billion years ago when no form of life was visible anywhere
on the surface, before the continents formed, before it even rained water.
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- But even during these earliest times life was stirring
- the microorganisms called cyanobacteria evolved.
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- As oxygen accumulated in the atmosphere the face of the
planet was changed. Life took a new course as it adapted to use the abundance
of oxygen.
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- Still around
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- We can still see the cyanobacteria today. They are often
visible as surface blooms in lakes or oceans but they live on in an even
more remarkable way.
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- Sometime in the past, perhaps a billion years ago, the
cyanobacteria teamed up with other cells.
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- Some of them started to live inside other cells exchanging
their freedom for an enclosed and stable environment inside another cell.
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- In turn, the host cells used the energy-producing ability
of the cyanobacteria and the two organisms began a symbiotic relationship
of mutual benefit.
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- So close has this relationship become that today we have
forgotton that a widespread form of life on Earth is actually two forms
of life working together.
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- The powerhouse of plant cells, the so-called chloroplast,
the part of the plant that makes it green, is a cyanobacterium.
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