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The Earth is 4.6 billion years old,
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but a human lifetime often lasts
for less than 100 years.
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So why care about
the history of our planet
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when the distant past seems
so inconsequential to everyday life?
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You see, as far as we can tell,
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Earth is the only planet
in our solar system
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known to have sparked life,
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and the only system able to provide
life support for human beings.
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So why Earth?
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We know Earth is unique
for having plate tectonics,
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liquid water on its surface
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and an oxygen-rich atmosphere.
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But this has not always been the case,
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and we know this because ancient rocks
have recorded the pivotal moments
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in Earth's planetary evolution.
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And one of the best places
to observe those ancient rocks
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is in the Pilbara of Western Australia.
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The rocks here are 3.5 billion years old,
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and they contain some of the oldest
evidence for life on the planet.
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Now, often when we think of early life,
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we might imagine a stegosaurus
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or maybe a fish crawling onto land.
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But the early life that I'm talking about
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is simple microscopic life, like bacteria.
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And their fossils are often preserved
as layered rock structures,
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called stromatolites.
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This simple form of life
is almost all we see in the fossil record
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for the first three billion years
of life on Earth.
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Our species can only be traced
back in the fossil record
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to a few hundred thousand years ago.
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We know from the fossil record,
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bacteria life had grabbed
a strong foothold
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by about 3.5 to four billion years ago.
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The rocks older than this
have been either destroyed
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or highly deformed
through plate tectonics.
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So what remains a missing
piece of the puzzle
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is exactly when and how
life on Earth began.
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Here again is that ancient
volcanic landscape in the Pilbara.
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Little did I know that our research here
would provide another clue
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to that origin-of-life puzzle.
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It was on my first field trip here,
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toward the end of a full,
long week mapping project,
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that I came across something
rather special.
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Now, what probably looks like
a bunch of wrinkly old rocks
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are actually stromatolites.
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And at the center of this mound
was a small, peculiar rock
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about the size of a child's hand.
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It took six months before we inspected
this rock under a microscope,
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when one of my mentors
at the time, Malcolm Walter,
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suggested the rock resembled geyserite.
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Geyserite is a rock type that only forms
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in and around the edges
of hot spring pools.
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Now, in order for you to understand
the significance of geyserite,
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I need to take you back
a couple of centuries.
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In 1871, in a letter
to his friend Joseph Hooker,
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Charles Darwin suggested:
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"What if life started
in some warm little pond
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with all sort of chemicals
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still ready to undergo
more complex changes?"
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Well, we know of warm little ponds.
We call them "hot springs."
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In these environments, you have hot water
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dissolving minerals
from the underlying rocks.
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This solution mixes with organic compounds
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and results in a kind of chemical factory,
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which researchers have shown
can manufacture simple cellular structures
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that are the first steps toward life.
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But 100 years after Darwin's letter,
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deep-sea hydrothermal vents, or hot vents,
were discovered in the ocean.
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And these are also chemical factories.
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This one is located along
the Tonga volcanic arc,
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1,100 meters below sea level
in the Pacific Ocean.
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The black smoke that you see billowing
out of these chimneylike structures
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is also mineral-rich fluid,
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which is being fed off by bacteria.
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And since the discovery
of these deep-sea vents,
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the favored scenario for an origin of life
has been in the ocean.
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And this is for good reason:
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deep-sea vents are well-known
in the ancient rock record,
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and it's thought that the early Earth
had a global ocean
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and very little land surface.
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So the probability that deep-sea vents
were abundant on the very early Earth
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fits well with an origin of life
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in the ocean.
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However ...
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our research in the Pilbara
provides and supports
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an alternative perspective.
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After three years, finally, we were
able to show that, in fact,
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our little rock was geyserite.
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So this conclusion suggested
not only did hot springs exist
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in our 3.5 billion-year-old
volcano in the Pilbara,
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but it pushed back evidence for life
living on land in hot springs
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in the geological record of Earth
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by three billion years.
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And so, from a geological perspective,
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Darwin's warm little pond
is a reasonable origin-of-life candidate.
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Of course, it's still debatable
how life began on Earth,
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and it probably always will be.
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But it is clear that it's flourished;
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it has diversified,
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and it has become ever more complex.
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Eventually, it reached
the age of the human,
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a species that has begun
to question its own existence
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and the existence of life elsewhere:
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Is there a cosmic community
waiting to connect with us,
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or are we all there is?
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A clue to this puzzle again
comes from the ancient rock record.
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At about 2.5 billion years ago,
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there is evidence that bacteria
had begun to produce oxygen,
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kind of like plants do today.
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Geologists refer to
the period that followed
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as the Great Oxidation Event.
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It is implied from rocks
called banded iron formations,
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many of which can be observed as
hundreds-of-meter-thick packages of rock
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which are exposed in gorges
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that carve their way through
the Karijini National Park
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in Western Australia.
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The arrival of free oxygen allowed
two major changes to occur on our planet.
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First, it allowed complex life to evolve.
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You see, life needs oxygen
to get big and complex.
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And it produced the ozone layer,
which protects modern life
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from the harmful effects
of the sun's UVB radiation.
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So in an ironic twist, microbial life
made way for complex life,
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and in essence, relinquished
its three-billion-year reign
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over the planet.
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Today, we humans dig up
fossilized complex life
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and burn it for fuel.
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This practice pumps vast amounts
of carbon dioxide into the atmosphere,
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and like our microbial predecessors,
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we have begun to make
substantial changes to our planet.
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And the effects of those
are encompassed by global warming.
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Unfortunately, the ironic twist here
could see the demise of humanity.
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And so maybe the reason
we aren't connecting with life elsewhere,
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intelligent life elsewhere,
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is that once it evolves,
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it extinguishes itself quickly.
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If the rocks could talk,
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I suspect they might say this:
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life on Earth is precious.
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It is the product of
four or so billion years
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of a delicate and complex co-evolution
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between life and Earth,
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of which humans only represent
the very last speck of time.
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You can use this information
as a guide or a forecast --
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or an explanation as to why it seems
so lonely in this part of the galaxy.
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But use it to gain some perspective
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about the legacy that you
want to leave behind
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on the planet that you call home.
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Thank you.
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(Applause)
Camille Martínez
The English transcript was updated on 12/11/19.
In the talk description:
western Australian --> Western Australian
Thank you!