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Columbus43219 t1_ixx19ny wrote

I love this question because it started a ball rolling in my head. No GPS... no lighthouses, the star charts would be off, the moon would be closer... the ocean currents were different... magnetic north was in a different place... sea levels were different...

I'd be starting from scratch.

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PatrickKieliszek t1_ixxbped wrote

We could work out the star charts to an accuracy where they would be useful. Only unpredictable thing would be the addition of some stars that have died in the last 500,000 years.

Those shouldn't be hard to screen out.

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skribe t1_ixxfl2s wrote

You'd probably need to bring along your own breathing apparatus too. IIRC 500 million years ago oxygen levels were about a fifth of today's levels.

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masher_oz t1_ixxtjr3 wrote

Looks like longer than 0.5 Ga ago, there's less oxygen in the atmosphere than there is now.

https://en.m.wikipedia.org/wiki/File:Oxygenation-atm-2.svg

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skribe t1_ixxuzmq wrote

Isn't that what I just said?

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imVision t1_ixz7s2b wrote

OK, but you’d need to bring in like a suit full of oxygen because the atmosphere only contained about 20% of the oxygen that today’s atmosphere has

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thetarget3 t1_ixz9qg7 wrote

You can calculate your latitude fairly easily by tracking the sun's shadow at noon every day until midsummer, or until it returns again if you're in the tropics. Longitude would be really hard though.

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