Hacker News Reader

Comment by sgt101 | Hacker News Reader

Gosh - imagine that place!

I wonder how old this world is, and how stable its enviroment is/has been. Complex animal life took 3.5 bn years to emerge on Earth, of course that's a meaningless data point by itself but intuitively for this place to have an ecosystem or complex life it needs to be old.

Still, even without this what a wonderful and weird environment.

View on HN

Single cell life appeared on Earth almost instantly after the planet cooled down enough to allow it. I don't think it's clear that any progress was being made over the next few billion years. One day the right mutation happened and boom, fancy life everywhere. With our data sample of one, I don't think it's clear if it was extraordinarily bad luck it took that long to happen, or extraordinarily good luck it ever happened at all.

Eukaryotic cell is such a bonkers insane development, I definitely lean towards the impossibly lucky scenario. There was no need for that to be the origin story of a mitochondria like organelle (https://en.wikipedia.org/wiki/Symbiogenesis), but that's what we think we have.

That being said, there was an experiment (https://www.pnas.org/doi/full/10.1073/pnas.1115323109) which was able to select single cellular organisms to "become multicellular" in a rapid amount of time (<50 generations? been a while since I read it). Which says to me that, theoretically, the process is not hard, it just requires trillions of attemps to evoke something that works.

It not only has to work, the mutant has to have a fitness advantage over the nonmutant or it will drop out of the population before long. The vast majority of mutations are also “bad.”

> 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.

> 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?

Yes but we’re talking about before the Cambrian

>>> 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?

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...

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-e...

The fossil record. There is little evidence of very complex animal life before about 541 million years ago, which is when the Cambrian explosion begun.

Given the surface of the planet is such a dynamic environment, I wonder how much evidence we should expect even if it did exist.

There's quite a few fossils showing single-celled organisms from 3+ billion years ago. I imagine if more complex life existed the fossils could've survived

When you say very little, do you mean none, or there is some questionable evidence?

I'm genuinely curious

Before "modern" life evolved in the pre-cambrian era, there was the Ediacaran life forms that were complex multicellular life, but died out millions of years before the Cambrian explosion.

https://en.wikipedia.org/wiki/Ediacaran_biota

Reply on news.ycombinator.com