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The Earth is 4.6 billion years old,

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but a human lifetime often lasts[br]for less than 100 years.

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So why care about[br]the history of our planet

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when the distant past seems[br]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[br]in our solar system

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known to have sparked life,

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and the only system able to provide[br]life support for human beings.

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So why Earth?

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We know Earth is unique[br]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[br]have recorded the pivotal moments

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in Earth's planetary evolution.

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And one of the best places[br]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[br]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[br]as layered rock structures,

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called stromatolites.

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This simple form of life[br]is almost all we see in the fossil record

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for the first three billion years[br]of life on Earth.

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Our species can only be traced[br]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[br]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[br]have been either destroyed

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or highly deformed[br]through plate tectonics.

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So what remains a missing[br]piece of the puzzle

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is exactly when and how[br]life on Earth began.

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Here again is that ancient[br]volcanic landscape in the Pilbara.

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Little did I know that our research here[br]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,[br]long week mapping project,

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that I came across something[br]rather special.

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Now, what probably looks like[br]a bunch of wrinkly old rocks

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are actually stromatolites.

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And at the center of this mound[br]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[br]this rock under a microscope,

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when one of my mentors[br]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[br]of hot spring pools.

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Now, in order for you to understand[br]the significance of geyserite,

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I need to take you back[br]a couple of centuries.

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In 1871, in a letter[br]to his friend Joseph Hooker,

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Charles Darwin suggested:

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"What if life started[br]in some warm little pond

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with all sort of chemicals

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still ready to undergo[br]more complex changes?"

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Well, we know of warm little ponds.[br]We call them "hot springs."

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In these environments, you have hot water

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dissolving minerals[br]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[br]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,[br]were discovered in the ocean.

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And these are also chemical factories.

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This one is located along[br]the Tonga volcanic arc,

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1,100 meters below sea level[br]in the Pacific Ocean.

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The black smoke that you see billowing[br]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[br]of these deep-sea vents,

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the favored scenario for an origin of life[br]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[br]in the ancient rock record,

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and it's thought that the early Earth[br]had a global ocean

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and very little land surface.

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So the probability that deep-sea vents[br]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[br]provides and supports

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an alternative perspective.

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After three years, finally, we were[br]able to show that, in fact,

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our little rock was geyserite.

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So this conclusion suggested[br]not only did hot springs exist

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in our 3.5 billion-year-old[br]volcano in the Pilbara,

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but it pushed back evidence for life[br]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[br]is a reasonable origin-of-life candidate.

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Of course, it's still debatable[br]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[br]the age of the human,

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a species that has begun[br]to question its own existence

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and the existence of life elsewhere:

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Is there a cosmic community[br]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[br]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[br]had begun to produce oxygen,

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kind of like plants do today.

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Geologists refer to[br]the period that followed

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as the Great Oxidation Event.

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It is implied from rocks[br]called banded iron formations,

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many of which can be observed as[br]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[br]the Karijini National Park

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in Western Australia.

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The arrival of free oxygen allowed[br]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[br]to get big and complex.

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And it produced the ozone layer,[br]which protects modern life

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from the harmful effects[br]of the sun's UVB radiation.

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So in an ironic twist, microbial life[br]made way for complex life,

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and in essence, relinquished[br]its three-billion-year reign

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over the planet.

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Today, we humans dig up[br]fossilized complex life

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and burn it for fuel.

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This practice pumps vast amounts[br]of carbon dioxide into the atmosphere,

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and like our microbial predecessors,

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we have begun to make[br]substantial changes to our planet.

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And the effects of those[br]are encompassed by global warming.

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Unfortunately, the ironic twist here[br]could see the demise of humanity.

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And so maybe the reason[br]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[br]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[br]the very last speck of time.

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You can use this information[br]as a guide or a forecast --

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or an explanation as to why it seems[br]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[br]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)