What would a tidally locked Earth be like?

[lpetrich]

A problem with that discussion. Day and night won't be all or nothing. It isn't all-or-nothing on our planet, and it won't be on an exoplanet with a thick-enough atmosphere.
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This is a function of the atmosphere. Night is very abrupt on an airless world.

True, but an airless world would not have a habitable surface.

 

[Loren Pechtel]

A problem with that discussion. Day and night won't be all or nothing. It isn't all-or-nothing on our planet, and it won't be on an exoplanet with a thick-enough atmosphere.
(details snipped for brevity)

This is a function of the atmosphere. Night is very abrupt on an airless world.

True, but an airless world would not have a habitable surface.

But it could be a fairly thin atmosphere. Plants put a very low demand on atmospheric resources, they could live so long as there's enough pressure to keep water from boiling.

 

[BH]

Just curious, how thin could our atmosphere be on Earth, with nothing else changing, and Earth be able to have liquid water on the surface?

 

[Loren Pechtel]

Just curious, how thin could our atmosphere be on Earth, with nothing else changing, and Earth be able to have liquid water on the surface?

Depends on the temperature. Water boils at body temperature at 44,000'. Liquid water can not exist above about 90,000'.