Earth holds more living cells than there are stars in the observable universe
Roughly ten to the power of 30 cells are alive on Earth right now, a million times more than the estimated stars in the observable universe. Life fills this thin shell almost everywhere, from rocks 19 kilometres underground to air 64 kilometres up, and hidden microbes may outweigh every plant and animal on the surface.
The biosphere is the sum of all Earth's ecosystems, the living layer of the planet together with its links to rock, ice, water and air. In matter it is almost sealed, with little coming in or leaving, but in energy it is wide open: photosynthesis captures sunlight at around 100 terawatts. The geologist Eduard Suess coined the word in 1875 for the part of Earth's surface where life dwells, and in the 1920s Vladimir Vernadsky gave it an ecological meaning, calling ecology the science of the biosphere.
Life seems to have started remarkably early. Biogenic graphite in Greenland rocks dates to 3.7 billion years ago, and microbial mats fossilised in Western Australian sandstone to 3.48 billion. More contested finds push further back, including possible microfossils from hydrothermal vent deposits in Quebec's Nuvvuagittuq Belt, reported in 2017 at up to 4.28 billion years old, not long after the oceans formed. The biologist Stephen Blair Hedges has argued that if life arose so quickly here, it could be common across the universe.
The extremes are startling. A Ruppell's vulture has been recorded at 11,300 metres, bar-headed geese migrate at over 8,300 metres, and fish live more than 8,000 metres down in the Puerto Rico Trench. Single-celled organisms inhabit the deepest part of the Mariana Trench, and some microbes have survived the vacuum of space in experiments. Prokaryotes alone may account for as much as 0.8 trillion tonnes of carbon out of a total biosphere of one to four trillion.
The term also stretches beyond Earth. Scientists apply it to any closed, self-regulating system containing ecosystems, including experimental habitats such as Biosphere 2 and BIOS-3, and the field studying such artificial worlds is called biospherics.
Source: Biosphere
