Hacker News Reader

Comment by scotty79 | Hacker News Reader

> A closed loop metabolism is indeed a good boundary marker.

Presence of metallic catalysts is just an environmental factor. Not counting the organisms that can't live without them as life would be as not counting as life something that can't do metabolism without liquid water.

Life at time of LUCA just had a bit stricter environment requirements, but it should still be counted as life.

So I wouldn't read this as discovering that life evolved twice. Life just evolved a hack for dealing with environments without metallic catalysts twice.

View on HN

Presence of metallic catalysts is just an environmental factor.

No, it isn’t quite that. For it to count as “environment” the organism must be able to survive for at least a time without it.

The issue here is, the metal wasn’t a nutrient. That would be fine and exactly like it is for all life now.

Instead the metal was the anchor. If an organism needed to grow on it to enable half its metabolism, it is at the least very distinct from current life.

The only issue with the “two origins” claim is both lineages, bacteria and archea, come from this, and even with an open metabolic chain, you already had the nucleic acid function etc all sorted out, and common between both kingdoms.

So it’s a stretch to say there were two origins to life, but not that this proto life is distinct from modern life. That we need things from our environment is not the same as what they found about proto life in the vents.

> For it to count as “environment” the organism must be able to survive for at least a time without it.

How long can a cell survive without liquid water? It literally enables almost all of the chemistry inside the cell.

Cell requiring a specific metal to be present is not very different from cell requiring for liquid water to be present.

Initially life started in favorable conditions, then spread to less favorable ones. Lack of metal catalyst around was the initial less favorable condition. At some point lack of liquid water was one. But eventually life spread to various very dry or cold places because it found workarounds for environment infeasibilities.

Maybe in 5 billion years life that can't survive without liquid water around and can't substitute it with self-made polar solvents and thus is stuck to surfaces of very few, very particular planets is going to be considered proto-life.

>How long can a cell survive without liquid water?

Depends on the cell, but it’s not instant death. By definition, a cell is a membrane with some water inside it.

Sure, move that cell to totally dry conditions and most will die. But not all, by any means. Bacterial endospores last millenia without water. Tardigrades can do years.

This isn’t quite the gotcha you think it is.

The metal use for multiple catalytic steps is distinct. The paper isn’t wrong about that at all. Trying to prove the closed loop metabolism of modern life is secretly open loop isn’t going to work because it isn’t open like that. An organism can survive without constant contact with any of its components. Sometimes not for very long, but nothing alive today is as dependent on something external as these proto cells were on reduced metal.

Reply on news.ycombinator.com