Plausible, but I remember when I did my degree, one of the examples given about the importance of choosing a good site for “off site backups” was a company whose main site was one of the WTO twin towers, whose off site was the the other tower on the grounds that they couldn’t conceive of anything that would affect both without also destroying civilisation as a whole.

Well sure, but that's always a question of what are you trying to defend yourself against(what kind of scenario is the backup helping with). Twin towers are probably good enough for any kind of fire/electrical failure/theft/vandalism, but not for a meteor strike, war or as we've seen - terrorism. It's not that people in your example were stupid and didn't see it - just that most likely they didn't consider those dangers as important to have a backup for(if a war breaks out or a meteor strikes New York you probably have bigger problems).

It's the same here - most of the "human extinction"-scale events really don't touch a base that's 10km under water or under ground. Nuclear war or meteor strike? nope. Earthquakes? There are places safe from that. Solar flares? Nope. Deadly virus? Quarantine everyone arriving like you would with the journey to Mars.

Terrorism remains the main risk, but it would have been the same risk on Mars too.

And most importantly - it teaches us how to run an independent colony deep underground, which is important because despite all the Sci-Fi films showing us otherwise, the base on Mars would really have to be underground because of radiation risk.

So yeah, sure, run an underground base for a few decades then you can just transplant the technology to Mars - don't start with Mars first.

> don't start with Mars first

On that part we definitely both agree :)

Although, I would say that developing the tech to colonise Mars can be a useful rallying point for tech useful to Earth (if you can put a city of a million on the red planet, you can also put it in the middle of the Himalayas or Antarctica or the Sahara), in the same way that Tesla is useful as a rallying point for electric cars despite all the people I hear complaining about the build quality.

Wouldn't earthquakes and even volcanoes still be an issue? I also imagine being at the bottom of the Gulf of Mexico was of no help when the dinosaur-killing asteroid hit.

Plus where does your energy come from? You don't have solar. You need to make your own light to grow food. Geothermal is possible I guess but the ocean is terrible for corrosion and building. The high pressure at the bottom of the ocean makes everything worse.

Except 8 billion starving desperate people trying to get it.

For instance if people were starving or hiding from fallout, those doomsday shelters the rich are building for themselves would likely be overran by the locals who helped build them or heard all about them from town gossip.

How are those 8 billion starving people getting into a base 10km below the surface of the ocean which requires a specialized submarine to get to? How is this any more realistic than 8 billion starving people getting to Mars?

And finally - I hope you aren't suggesting that the base on Mars is a way to escape "8 billion starving people".

You don't have to get to it to affect it. Eight billion very pissed off people can probably figure out how to drop rocks on the rich billionaire haven in an ocean trench.

A few of those people getting access to a submarine or just building a robot to go down there is a lot more likely than them building a vehicle and equipment to land on Mars and assault the habitat there.

I think we're talking about different kinds of scale here. A habitat that could be destroyed by "a few people building a submarine" isn't a backup policy for humanity. Not here, not on Mars, not anywhere. I'm imagining a proper city-sized habitation for few million people - with industry and agriculture to support it. A truly separate colony that trades with the rest of Earth when it needs to, but can survive on its own.

Also I really don't like how the arguments so far are about preventing the starving people from coming over and messing things up. It strikes me as very "we need to keep the pleb out" kind of thinking, no different than what some rich people are doing.

I can think of some things that would require them to stay there, unable to surface, for thousands of years. Having the ability to mine asteroids and create additional colonies and space stations seems better to me.

....just mine around your base? Create tunnels that span the entire planet if you must? How is all of this not easier than something as exotic as asteroid mining?

Even if the entire surface is irradiated(somehow) you can still launch things into space with underground railguns. It's not what we currently use, but it's easier to imagine this than building a base on Mars with current(or near future) technology.

Just put the DC backup in that rack in the corner, should be all we need.