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Not certain at all, it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record.

wolverine876 3y ago
> it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record. I thought the Cambrian Explosion's fossil record was pretty sizeable - in fact, it's named after the place where the fossil layer was first discovered. I didn't know it was related to a common ancestor. Are you thinking of something else or am I missing something major?
- edgyquant 3y ago
  Yes but we’re talking about before the Cambrian
  - wolverine876 3y ago
    ? >>> Complex animal life took 3.5 bn years to emerge on Earth, >> How certain are we it took that long (the first time)? > Not certain at all, it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record. Do you mean, there's little evidence of pre-Cambrian absence? Absence of evidence is some evidence of absence, in this case. But how does LUCA fit into this question?
    - sgt101 3y ago
      I think we can see where different complex animals split in their evolutionary tree - so humans and starfish split a long way back. Then we use a standard mutation clock to estimate how long ago that was. If all complex animals split from simple animals an estimated 700m years ago...
no_wizard 3y ago
Its possible there is a good explanation for why there would be no strong fossil record[0] for an advanced civilization preceding us. >When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old—older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. While I think its highly unlikely (I mean less than 0.00001% possible) the means in which we would could even detect it are complicated [0]: https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e...

wolverine876 3y ago

> it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record. I thought the Cambrian Explosion's fossil record was pretty sizeable - in fact, it's named after the place where the fossil layer was first discovered. I didn't know it was related to a common ancestor. Are you thinking of something else or am I missing something major?

edgyquant 3y ago
Yes but we’re talking about before the Cambrian
- wolverine876 3y ago
  ? >>> Complex animal life took 3.5 bn years to emerge on Earth, >> How certain are we it took that long (the first time)? > Not certain at all, it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record. Do you mean, there's little evidence of pre-Cambrian absence? Absence of evidence is some evidence of absence, in this case. But how does LUCA fit into this question?
  - sgt101 3y ago
    I think we can see where different complex animals split in their evolutionary tree - so humans and starfish split a long way back. Then we use a standard mutation clock to estimate how long ago that was. If all complex animals split from simple animals an estimated 700m years ago...

no_wizard 3y ago

Its possible there is a good explanation for why there would be no strong fossil record[0] for an advanced civilization preceding us. >When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old—older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. While I think its highly unlikely (I mean less than 0.00001% possible) the means in which we would could even detect it are complicated [0]: https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e...