Plural of biosphere; all the regions of Earth where life exists, or enclosed systems designed to contain living ecosystems.
From 'bio-' (life) + 'sphere' (globe or layer, from Greek 'sphaira'). The term was popularized in the 1920s-1930s to describe the complete realm where life operates on Earth.
Biosphere 2, an enormous sealed greenhouse in Arizona, proved how hard it is to replicate Earth's biosphere—the system crashed repeatedly until people understood that our real biosphere is so intricately interconnected that isolating parts of it becomes nearly impossible to manage!
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