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← How did plants change our planet? | California Academy of Sciences

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Showing Revision 9 created 08/01/2019 by Cristina Castillo.

  1. ♪ (music) ♪
  2. Today, my job is easy.
  3. I get to tell you about my favorite thing
    in the world, plants,
  4. the very first land plants to be exact.
  5. It's a lovely story about how over time
  6. tiny plants gave rise
    to more complex plants
  7. that basically changed the world.
  8. Let's go back millions
    and millions of years.
  9. We're not going to see
    the dinosaurs, sorry.
  10. We're going to go back further in time,
    to the time of the very first land plants.
  11. I wouldn't want to live here,
    but who would?
  12. These plants would.
  13. The first plants on land were tiny.
  14. They didn't have roots
    or a vascular system.
  15. Plants use roots
    to take up water from the soil.
  16. Because these early plants
    didn't have roots,
  17. they had to live close to water,
  18. like rivers and ponds.
  19. A vascular system is how water
    and nutrients are moved around a plant.
  20. Without this plumbing,
    plants can't grow very large,
  21. because some parts won't get water.
  22. The first plants were similar to mosses
    and liverworts that we see today.
  23. They also don't have real roots.
  24. So, after a few million years,
    plants develop roots and plumbing.
  25. The roots allow them to tap
    into water in the ground,
  26. helping them move away
    from wetter areas.
  27. With pipes to carry water up the stem,
  28. plants can grow taller and taller
  29. as they start to compete
    with each other for sunlight.
  30. And here's where the story
    gets really interesting.
  31. As plants develop roots,
  32. they physically and chemically
    change the surface of our planet.
  33. First, they create soil.
  34. Roots penetrate
    the rocky exterior at the surface,
  35. and as they grow deeper and deeper,
  36. they break the rock up
    into smaller and smaller pieces.
  37. The roots also use
    carbon dioxide to produce acid
  38. that breaks down the rock even further.
  39. Finally, as plants die and decay,
    they add nutrients,
  40. making the soil much richer.
  41. But that's not all
    these early land plants are doing,
  42. they're also affecting the climate.
  43. Plants take in carbon dioxide
    from the atmosphere.
  44. Through photosynthesis,
    plants use light from the sun
  45. to convert that carbon dioxide
    plus water into sugar and oxygen.
  46. They release the oxygen
    back into the atmosphere,
  47. but they use energy
    from the sugar to grow.
  48. A lot of the sugar becomes
    the raw material
  49. that makes up the structure of the plant,
  50. essentially locking up the carbon
    from the carbon dioxide
  51. it originally absorbed in its tissues.
  52. When the plants die,
    they rot on the ground
  53. and some of that plant material,
    including its carbon,
  54. gets trapped in the soil.
  55. But wait, there's more!
  56. Remember how the plants
    used carbon dioxide to produce acid?
  57. Well, that reacts with the rocky soil,
    trapping even more carbon dioxide.
  58. The carbon dioxide in the atmosphere
    keeps our planet warm,
  59. so with less of it in the air,
  60. the planet slowly cools down
    during this period.
  61. See how plants drastically transformed
    our planet forever?
  62. We actually have evidence
    for most of this story.
  63. So as delicate and flimsy
    as these plants were,
  64. we do have fossils of them.
  65. How do we know they're plants?
  66. Well, because they look a lot like
    the plants we still have nowadays.
  67. Here we have a living liverwort,
  68. and here's a magnification
    of a fossil one.
  69. So this shows us that plants
    were really small,
  70. without pipes and without roots.
  71. So when plants developed
    roots and plumbing,
  72. they could grow in different places,
    and they also get more sturdy.
  73. So that means the fossil record
    gets better and better?
  74. - Mm-hmm.
    - What are we looking at here, Cindy?
  75. Well, here I have a fossil of a plant
    that was still relatively small.
  76. Here are the stems,
  77. and you can see
    that it wasn't getting very big.
  78. Now, compare that with this younger one.
  79. This is a stem as well;
  80. it's a cross-section
    of its trunk actually.
  81. So this was a tree,
  82. and we also have the branches
    that grew on it, over here.
  83. We have fossilized soil too.
  84. And we can see plants forming soil
    from volcanic rock today.
  85. We can use that information
    to understand
  86. how early land plants created soil.
  87. At the same time as plants
    are getting bigger and bigger,
  88. the temperature of the planet
    starts to drop.
  89. This is where the evidence for this lies
  90. in the shells of ancient marine organisms.
  91. What's amazing is that scientists
    can actually measure the temperature
  92. of the environment
    where these shells formed.
  93. And we can do the same
    with fossil soil too.
  94. See how plants drastically transformed
    our planet forever?
  95. Thanks, plants!
  96. ♪ (gentle music) ♪