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

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Showing Revision 10 created 12/11/2019 by Camille Martínez.

  1. The Earth is 4.6 billion years old,
  2. but a human lifetime often lasts
    for less than 100 years.
  3. So why care about
    the history of our planet
  4. when the distant past seems
    so inconsequential to everyday life?
  5. You see, as far as we can tell,
  6. Earth is the only planet
    in our solar system
  7. known to have sparked life,
  8. and the only system able to provide
    life support for human beings.
  9. So why Earth?

  10. We know Earth is unique
    for having plate tectonics,
  11. liquid water on its surface
  12. and an oxygen-rich atmosphere.
  13. But this has not always been the case,
  14. and we know this because ancient rocks
    have recorded the pivotal moments
  15. in Earth's planetary evolution.
  16. And one of the best places
    to observe those ancient rocks
  17. is in the Pilbara of Western Australia.
  18. The rocks here are 3.5 billion years old,
  19. and they contain some of the oldest
    evidence for life on the planet.
  20. Now, often when we think of early life,

  21. we might imagine a stegosaurus
  22. or maybe a fish crawling onto land.
  23. But the early life that I'm talking about
  24. is simple microscopic life, like bacteria.
  25. And their fossils are often preserved
    as layered rock structures,
  26. called stromatolites.
  27. This simple form of life
    is almost all we see in the fossil record
  28. for the first three billion years
    of life on Earth.
  29. Our species can only be traced
    back in the fossil record
  30. to a few hundred thousand years ago.
  31. We know from the fossil record,
  32. bacteria life had grabbed
    a strong foothold
  33. by about 3.5 to four billion years ago.
  34. The rocks older than this
    have been either destroyed
  35. or highly deformed
    through plate tectonics.
  36. So what remains a missing
    piece of the puzzle
  37. is exactly when and how
    life on Earth began.
  38. Here again is that ancient
    volcanic landscape in the Pilbara.
  39. Little did I know that our research here
    would provide another clue
  40. to that origin-of-life puzzle.
  41. It was on my first field trip here,

  42. toward the end of a full,
    long week mapping project,
  43. that I came across something
    rather special.
  44. Now, what probably looks like
    a bunch of wrinkly old rocks
  45. are actually stromatolites.
  46. And at the center of this mound
    was a small, peculiar rock
  47. about the size of a child's hand.
  48. It took six months before we inspected
    this rock under a microscope,
  49. when one of my mentors
    at the time, Malcolm Walter,
  50. suggested the rock resembled geyserite.
  51. Geyserite is a rock type that only forms
  52. in and around the edges
    of hot spring pools.
  53. Now, in order for you to understand
    the significance of geyserite,

  54. I need to take you back
    a couple of centuries.
  55. In 1871, in a letter
    to his friend Joseph Hooker,
  56. Charles Darwin suggested:
  57. "What if life started
    in some warm little pond
  58. with all sort of chemicals
  59. still ready to undergo
    more complex changes?"
  60. Well, we know of warm little ponds.
    We call them "hot springs."

  61. In these environments, you have hot water
  62. dissolving minerals
    from the underlying rocks.
  63. This solution mixes with organic compounds
  64. and results in a kind of chemical factory,
  65. which researchers have shown
    can manufacture simple cellular structures
  66. that are the first steps toward life.
  67. But 100 years after Darwin's letter,

  68. deep-sea hydrothermal vents, or hot vents,
    were discovered in the ocean.
  69. And these are also chemical factories.
  70. This one is located along
    the Tonga volcanic arc,
  71. 1,100 meters below sea level
    in the Pacific Ocean.
  72. The black smoke that you see billowing
    out of these chimneylike structures
  73. is also mineral-rich fluid,
  74. which is being fed off by bacteria.
  75. And since the discovery
    of these deep-sea vents,
  76. the favored scenario for an origin of life
    has been in the ocean.
  77. And this is for good reason:
  78. deep-sea vents are well-known
    in the ancient rock record,
  79. and it's thought that the early Earth
    had a global ocean
  80. and very little land surface.
  81. So the probability that deep-sea vents
    were abundant on the very early Earth
  82. fits well with an origin of life
  83. in the ocean.
  84. However ...

  85. our research in the Pilbara
    provides and supports
  86. an alternative perspective.
  87. After three years, finally, we were
    able to show that, in fact,
  88. our little rock was geyserite.
  89. So this conclusion suggested
    not only did hot springs exist
  90. in our 3.5 billion-year-old
    volcano in the Pilbara,
  91. but it pushed back evidence for life
    living on land in hot springs
  92. in the geological record of Earth
  93. by three billion years.
  94. And so, from a geological perspective,
  95. Darwin's warm little pond
    is a reasonable origin-of-life candidate.
  96. Of course, it's still debatable
    how life began on Earth,

  97. and it probably always will be.
  98. But it is clear that it's flourished;
  99. it has diversified,
  100. and it has become ever more complex.
  101. Eventually, it reached
    the age of the human,
  102. a species that has begun
    to question its own existence
  103. and the existence of life elsewhere:
  104. Is there a cosmic community
    waiting to connect with us,
  105. or are we all there is?
  106. A clue to this puzzle again
    comes from the ancient rock record.

  107. At about 2.5 billion years ago,
  108. there is evidence that bacteria
    had begun to produce oxygen,
  109. kind of like plants do today.
  110. Geologists refer to
    the period that followed
  111. as the Great Oxidation Event.
  112. It is implied from rocks
    called banded iron formations,
  113. many of which can be observed as
    hundreds-of-meter-thick packages of rock
  114. which are exposed in gorges
  115. that carve their way through
    the Karijini National Park
  116. in Western Australia.
  117. The arrival of free oxygen allowed
    two major changes to occur on our planet.
  118. First, it allowed complex life to evolve.

  119. You see, life needs oxygen
    to get big and complex.
  120. And it produced the ozone layer,
    which protects modern life
  121. from the harmful effects
    of the sun's UVB radiation.
  122. So in an ironic twist, microbial life
    made way for complex life,
  123. and in essence, relinquished
    its three-billion-year reign
  124. over the planet.
  125. Today, we humans dig up
    fossilized complex life
  126. and burn it for fuel.
  127. This practice pumps vast amounts
    of carbon dioxide into the atmosphere,
  128. and like our microbial predecessors,
  129. we have begun to make
    substantial changes to our planet.
  130. And the effects of those
    are encompassed by global warming.
  131. Unfortunately, the ironic twist here
    could see the demise of humanity.

  132. And so maybe the reason
    we aren't connecting with life elsewhere,
  133. intelligent life elsewhere,
  134. is that once it evolves,
  135. it extinguishes itself quickly.
  136. If the rocks could talk,

  137. I suspect they might say this:
  138. life on Earth is precious.
  139. It is the product of
    four or so billion years
  140. of a delicate and complex co-evolution
  141. between life and Earth,
  142. of which humans only represent
    the very last speck of time.
  143. You can use this information
    as a guide or a forecast --
  144. or an explanation as to why it seems
    so lonely in this part of the galaxy.
  145. But use it to gain some perspective
  146. about the legacy that you
    want to leave behind
  147. on the planet that you call home.
  148. Thank you.

  149. (Applause)