How exactly would a thicker atmosphere make a planet more habitable than Earth?

My friend said an atmosphere 3 times Earths current one on another world would increase the change for life especially in the oceans based on currents. I thought the transport of cold to warm water is dependent on temperature. A thicker atmosphere would decrease temperature differences. Water may only vary between... show more My friend said an atmosphere 3 times Earths current one on another world would increase the change for life especially in the oceans based on currents. I thought the transport of cold to warm water is dependent on temperature. A thicker atmosphere would decrease temperature differences. Water may only vary between 90 and 50 degrees with a thicker atmosphere instead of the 100 and 28 degrees it has now. So wouldn’t an increase in atmospheric pressure decrease chances for life?
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