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This ancient rock is changing our theory on the origin of life

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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)
Title:
This ancient rock is changing our theory on the origin of life
Speaker:
Tara Djokic
Description:

Exactly when and where did life on Earth begin? Scientists have long thought that it emerged three billion years ago in the ocean -- until astrobiologist Tara Djokic and her team made an unexpected discovery in the Western Australian desert. Learn how an ancient rock found near a hot volcanic pool is shifting our understanding of the origin-of-life puzzle.

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Video Language:
English
Team:
TED
Project:
TEDTalks
Duration:
09:30
  • The English transcript was updated on 12/11/19.

    In the talk description:
    western Australian --> Western Australian

    Thank you!

English subtitles

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