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Discovery of world's oldest animals -

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Reporter: David Mark

BRENDAN TREMBATH: Scientists working in Oman have discovered evidence of the earliest animal life
on earth. The fossils are thought to belong to a type of sponge that lived at least 635-million
years ago.

The discovery highlights a problem the famous naturalist Charles Darwin considered in his seminal
work, 'The Origin of Species'. Darwin wondered why fully formed animals suddenly appeared around
540-million years ago.

As David Mark explains, the latest discovery points to the primitive animals Darwin predicted must
have come first.

DAVID MARK: The discovery of 635-million-year-old sponges has been described today in a paper
published in the journal 'Nature' by professor Gordon Love from the University of California.

In an accompanying article, Dr Jochen Brocks from the Research School of Earth Sciences at the
Australian National University explains the significance of Professor Love's discoveries.

JOCHEN BROCKS: He discovered what's now the oldest evidence of the earliest animals ever discovered
in the geological record. And there's in principle three different ways to detect an organism in
the geological record. The first one is trace fossils, for example if an animal crawls over the
ocean floor it will leave a trail. The second possibility to detect an animal is a normal fossil of
a shell, of a bone or even of soft tissue.

What Gordon Love found is molecular fossils and that's very good evidence for the existence of
sponges.

DAVID MARK: You mention that these animals were sponges. Is it possible to describe them? Do you
have any sense of what they might have looked like and how they might have lived and fed?

JOCHEN BROCKS: Now that's a very good question. It all depends on the tree of life. It is quite
possible that these molecules were produced by real sponges. There might have been tiny little
organisms sitting on the ocean floor, filtering organic matter out of the water, dead organisms.

And they already had a little channel in the middle that means they sucked water through their side
walls and pumped it out of the middle.

DAVID MARK: You said earlier that these are the earliest known animals that have been discovered so
how far back now are we taking that picture of when animals first evolved on earth?

JOCHEN BROCKS: Okay so the date that we have is that the oldest of these molecules must be older
than 635-million years. And well it's quite possible. In Oman the rocks stop just below there
somewhere so we can't get the record in Oman much, much older.

But there's other rocks in other places of the world where there's rocks 700-million years,
800-million years, 900-million years that are very well preserved where we could get molecules. And
we have to test all these rocks whether we still can find these sponge biomarkers.

The amazing things about the date 635-million years is that it was the age of the Marinoan
Glaciation, that is the greatest glaciations in earth history. Some people say it was a snowball
earth where the ocean was totally frozen over, about 2km deep at the Equator.

And so it's quite staggering that we can find evidence for animals, probably macroscopic animals
before this glaciation.

DAVID MARK: Because previously it had been thought that animals more than single-cell organisms had
evolved after this massive glaciation period; is that correct?

JOCHEN BROCKS: It looked like it. That's right.

DAVID MARK: And coincidentally next week marks the 200th anniversary of Charles Darwin's birth. And
this discovery actually ties in quite nicely with a conundrum that Charles Darwin described.

JOCHEN BROCKS: Yeah, that's actually quite nice. So in his 'Origin of Species', Charles Darwin
spent an entire chapter about one very worrying thing. If you take a look at the fossil record,
yeah it seems animals become smaller and more primitive if you look at older and older rocks. But
then in the Cambrian, at around 540-million years, the fossils seem to disappear all together.

And Darwin would have predicted there must have been hundreds and hundreds of millions of years of
evolution before the first animals in the Cambrian appeared but there was just nothing to be found.
There was no fossils.

And now we know that well, animals existed quite a bit much longer than this. The problem is they
didn't produce any hard skeletons or teeth. They were very small and they fossilised very, very
badly.

So in this sense Darwin is vindicated. His concerns were founded but he's totally vindicated.

DAVID MARK: What to your mind is the real significance of this discovery?

JOCHEN BROCKS: The real significance is that we might be able to make theories about how the oceans
have changed. It seems that the very ancient oceans on earth were very different from modern
oceans. They were almost like a turbid, stagnating pond.

And then animals came along - suspension feeders and sponges that started filtering the water and
clearing the water out. That's really, really significant. If we can bring the change of the ocean
from a turbid state to a clear water state, if we can correlate that somehow with the appearance of
sponges, it would be quite an amazing confirmation of his theory that animals changed the ocean
forever.

BRENDAN TREMBATH: Dr Jochen Brocks from the Research School of Earth Sciences at the Australian
National University, talking to David Mark.