BBC Learnings · Section 11

Did a civilisation exist on Earth before humans

Phil, do you believe there's life on other planets? Well, there's a lot of other planets,

Level: B1 · 72 sentences

Transcript

  1. Phil, do you believe there's life on other planets?
  2. Well, there's a lot of other planets,
  3. so yeah, I think there must be. Yeah, I agree.
  4. Well, it's a question that interests American astrophysicist Adam Frank,
  5. who discussed it with his colleague Gavin Schmidt,
  6. director of NASA's Institute for Space Studies.
  7. Here, Adam recalls their conversation for BBC World Service programme CrowdScience.
  8. We know that there's been no other civilisation on Earth,
  9. and he stopped me and said, how do you know that?
  10. And my jaw just dropped down to the floor.
  11. Adam's jaw dropped. An idiom for when someone looks shocked and surprised.
  12. Could there have been a technologically advanced civilisation before us here on Earth?
  13. It may sound weird, but this idea has a scientific name.
  14. Here is Caroline Steele, presenter of BBC's CrowdScience, to explain.
  15. The Silurian hypothesis proposes that if there was a technologically advanced civilisation hundreds of millions of years ago,
  16. we wouldn't be able to find traces of it.
  17. A hypothesis is an idea which explains how something happens
  18. and can be tested to find out if it's correct.
  19. In this episode, we'll be discussing the Silurian hypothesis,
  20. the idea that a technologically advanced civilization existed before us on Earth,
  21. but vanished without leaving a trace.
  22. Human civilisation is thousands of years old, but the planet itself is much older.
  23. So how old do scientists think the Earth is?
  24. Is it a three and a half billion years,
  25. b four and a half billion years,
  26. or c five and a half billion years?
  27. I'm going to guess c. five and a half billion years.
  28. OK, well, we will find the answer out later in the programme.
  29. To believe a technologically advanced civilisation existed on Earth hundreds of millions of years ago,
  30. most people would probably want evidence.
  31. We have evidence about other species from the past,
  32. such as the dinosaurs, from fossils.
  33. the remains of prehistoric plants or animals that have been preserved in rock for a very long time.
  34. But according to Adam Frank, fossils won't help prove the Silurian hypothesis,
  35. as he explains here to BBC World Service programme CrowdScience.
  36. Most things are not fossilised. It's only a tiny fraction of Earth's life that has ever become fossilised.
  37. So imagine that you have a 10,000-year-long civilisation,
  38. which is a blink of the eye for geology,
  39. that's too short to really create a lot of fossils.
  40. Adam argues that only a tiny fraction, meaning a very small amount, of life on Earth has turned into fossil.
  41. In geological time, even a 10,000-year-old civilisation is the blink of an eye,
  42. an idiom meaning a very short period of time.
  43. In other words, older civilisations might have existed on Earth,
  44. but not for long enough to leave fossilised evidence.
  45. However, not everyone is convinced by Adam's ideas.
  46. Evidence of our own civilisation, including plastics and man-made materials like concrete,
  47. is already being layered into the Earth's crust,
  48. and these are going to last a very long time.
  49. So surely a technologically advanced civilisation from prehistory would have left similar marks.
  50. Well, here's Adam Frank again answering these objections on BBC World Service programme CrowdScience.
  51. What happens is somebody else will pick up on their work,
  52. either affirming it and showing new evidence for it or pushing back on it.
  53. And once you get to like...
  54. 20, 30, 40 papers, then you have a consensus.
  55. You're like, OK, we've really, really looked at this and now we don't.
  56. Adam welcomes new evidence, even evidence which contradicts his ideas,
  57. as part of the scientific method needed to prove a hypothesis right or wrong.
  58. It's how scientists form a consensus, meaning a general agreement about the issue.
  59. Personally, I think the idea of prehistoric civilisations on Earth is so mysterious. It's OK to keep an open mind.
  60. Now, isn't it time you revealed the answer to your question, Beth?
  61. I think it is. I asked you how old do scientists think the Earth is?
  62. You said five and a half billion years and I'm afraid you were wrong, Phil.
  63. It's four and a half billion years.
  64. OK, let's recap the vocabulary we've learnt, starting with the idiom,
  65. my jaw dropped, which is used to say someone looks very shocked and surprised.
  66. A hypothesis is a suggestion that's proposed to explain something,
  67. which can then be tested to see if it's true.
  68. Fossils are the remains of prehistoric plants
  69. or animals that have been preserved in rock for a very long time.
  70. A tiny fraction of something is a very small amount of it.
  71. The idiom the blink of an eye means a very short period of time.
  72. And finally, a consensus is a general agreement.