Biosphere
The biosphere (from Greek βίος bíos "life" and σφαῖρα sphaira "sphere"), also known as the ecosphere (from Greek οἶκος oîkos "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also be termed the zone of life on Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to matter,[1] with minimal inputs and outputs. Regarding energy, it is an open system, with photosynthesis capturing solar energy at a rate of around 100 terawatts.[2] By the most general biophysiological definition, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, cryosphere, hydrosphere, and atmosphere. The biosphere is postulated to have evolved, beginning with a process of biopoiesis (life created naturally from non-living matter, such as simple organic compounds) or biogenesis (life created from living matter), at least some 3.5 billion years ago.[3][4]
This article is about the sum of all ecosystems. For the sum of all planetary spheres, see Ecosphere (planetary). For other uses, see Biosphere (disambiguation).In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as Biosphere 2 and BIOS-3, and potentially ones on other planets or moons.[5]
Earth's biosphere
Overview
Currently, the total number of living cells on the Earth is estimated to be 1030; the total number since the beginning of Earth, as 1040, and the total number for the entire time of a habitable planet Earth as 1041.[9][10] This is much larger than the total number of estimated stars (and Earth-like planets) in the observable universe as 1024, a number which is more than all the grains of beach sand on planet Earth;[11][12][13][14] but less than the total number of atoms estimated in the observable universe as 1082;[15] and the estimated total number of stars in an inflationary universe (observed and unobserved), as 10100.[16]
Experimental biospheres, also called closed ecological systems, have been created to study ecosystems and the potential for supporting life outside the Earth. These include spacecraft and the following terrestrial laboratories:
Extraterrestrial biospheres
No biospheres have been detected beyond the Earth; therefore, the existence of extraterrestrial biospheres remains hypothetical. The rare Earth hypothesis suggests they should be very rare, save ones composed of microbial life only.[45] On the other hand, Earth analogs may be quite numerous, at least in the Milky Way galaxy, given the large number of planets.[46] Three of the planets discovered orbiting TRAPPIST-1 could possibly contain biospheres.[47] Given limited understanding of abiogenesis, it is currently unknown what percentage of these planets actually develop biospheres.
Based on observations by the Kepler Space Telescope team, it has been calculated that provided the probability of abiogenesis is higher than 1 to 1000, the closest alien biosphere should be within 100 light-years from the Earth.[48]
It is also possible that artificial biospheres will be created in the future, for example with the terraforming of Mars.[49]