In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such asBiosphere 2 andBIOS-3, and potentiallyones on other planets or moons.[5]
Geochemists define the biosphere as being the total sum of living organisms (the "biomass" or "biota" as referred to by biologists and ecologists). In this sense, the biosphere is but one of four separate components of the geochemical model, the other three beinggeosphere,hydrosphere, andatmosphere. When these four component spheres are combined into one system, it is known as theecosphere. This term was coined during the 1960s and encompasses both biological and physical components of the planet.[7]
The Second International Conference on Closed Life Systems definedbiospherics as the science and technology of analogs andmodels of Earth's biosphere; i.e., artificial Earth-like biospheres.[8] Others may include the creation of artificial non-Earth biospheres—for example, human-centered biospheres or a nativeMartian biosphere—as part of the topic of biospherics.[9]
Currently, the total number ofliving 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 ahabitable planet Earth as 1041.[10][11] 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;[12][13][14][15] but less than the total number of atoms estimated in the observable universe as 1082;[16] and the estimated total number of stars in aninflationary universe (observed and unobserved), as 10100.[17]
Every part of the planet, from thepolar ice caps to theequator, features life of some kind. Recent advances inmicrobiology have demonstrated that microbes live deep beneath the Earth's terrestrial surface and that the total mass ofmicrobial life in so-called "uninhabitable zones" may, inbiomass, exceed all animal and plant life on the surface. The actual thickness of the biosphere on Earth is difficult to measure. Birds typically fly at altitudes as high as 1,800 m (5,900 ft; 1.1 mi) and fish live as much as 8,372 m (27,467 ft; 5.202 mi) underwater in thePuerto Rico Trench.[3]
There are more extreme examples for life on the planet:Rüppell's vulture has been found ataltitudes of 11,300 metres (37,100 feet; 7.0 miles);bar-headed geese migrate at altitudes of at least 8,300 m (27,200 ft; 5.2 mi);yaks live at elevations as high as 5,400 m (17,700 ft; 3.4 mi) above sea level;mountain goats live up to 3,050 m (10,010 ft; 1.90 mi). Herbivorous animals at these elevations depend on lichens, grasses, and herbs.
Life forms live in every part of the Earth's biosphere, includingsoil,hot springs,inside rocks at least 19 km (12 mi) deep underground, and at least 64 km (40 mi) high in the atmosphere.[27][28][29] Marine life under many forms has been found in the deepest reaches of theworld ocean while much of thedeep sea remains to be explored.[30]
Under certain test conditions, microorganisms have been observed tosurvive the vacuum of outer space.[31][32] The total amount of soil and subsurface bacterialcarbon is estimated as 5 × 1017 g.[27] The mass ofprokaryote microorganisms—which includes bacteria and archaea, but not the nucleatedeukaryote microorganisms—may be as much as 0.8 trillion tons of carbon (of the total biospheremass, estimated at between 1 and 4 trillion tons).[33]Barophilic marine microbes have been found at more than a depth of 10,000 m (33,000 ft; 6.2 mi) in theMariana Trench, the deepest spot in the Earth's oceans.[34] In fact, single-celled life forms have been found in the deepest part of the Mariana Trench, by theChallenger Deep, at depths of 11,034 m (36,201 ft; 6.856 mi).[35][36][37] Other researchers reported related studies that microorganisms thrive inside rocks up to 580 m (1,900 ft; 0.36 mi) below the sea floor under 2,590 m (8,500 ft; 1.61 mi) of ocean off the coast of thenorthwestern United States,[36][38] as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan.[39] Culturable thermophilic microbes have been extracted from cores drilled more than 5,000 m (16,000 ft; 3.1 mi) into theEarth's crust inSweden,[40] from rocks between 65–75 °C (149–167 °F). Temperatureincreases with increasing depth into the Earth's crust. The rate at which the temperature increases depends on many factors, including the type of crust (continental vs. oceanic), rock type, geographic location, etc. The greatest known temperature at which microbial life can exist is 122 °C (252 °F) (Methanopyrus kandleri Strain 116). It is likely that the limit of life in the "deep biosphere" is defined by temperature rather than absolute depth.[citation needed] On 20 August 2014, scientists confirmed the existence of microorganisms living 800 m (2,600 ft; 0.50 mi) below the ice ofAntarctica.[41][42]
Earth's biosphere is divided into severalbiomes, inhabited by fairly similarflora andfauna. On land, biomes are separated primarily bylatitude. Terrestrial biomes lying within theArctic andAntarctic Circles are relatively barren ofplant andanimal life. In contrast, most of the more populous biomes lie near theequator.
On land, vegetation appears on a scale from brown (low vegetation) to dark green (heavy vegetation); at the ocean surface, phytoplankton are indicated on a scale from purple (low) to yellow (high). This visualization was created with data from satellites including SeaWiFS, and instruments including the NASA/NOAA Visible Infrared Imaging Radiometer Suite and the Moderate Resolution Imaging Spectroradiometer.
Experimental biospheres, also calledclosed 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:
No biospheres have been detected beyond the Earth; therefore, the existence of extraterrestrial biospheres remains hypothetical. Therare Earth hypothesis suggests they should be very rare, save ones composed ofmicrobial life only.[46] On the other hand,Earth analogs may be quite numerous, at least in theMilky Way galaxy, given the large number of planets.[47] Three of the planets discovered orbitingTRAPPIST-1 could possibly contain biospheres.[48] Given limited understanding ofabiogenesis, it is currently unknown what percentage of these planets actually develop biospheres.
Based on observations by theKepler 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.[49]
It is also possible that artificial biospheres will be created in the future, for example with theterraforming of Mars.[50]
^abCampbell, Neil A.; Brad Williamson; Robin J. Heyden (2006).Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall.ISBN978-0-13-250882-7.Archived from the original on 2014-11-02. Retrieved2008-09-14.
^Glud, Ronnie; Wenzhöfer, Frank; Middelboe, Mathias; Oguri, Kazumasa; Turnewitsch, Robert; Canfield, Donald E.; Kitazato, Hiroshi (17 March 2013). "High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth".Nature Geoscience.6 (4):284–288.Bibcode:2013NatGe...6..284G.doi:10.1038/ngeo1773.
GLOBIO.info, anongoing programme to map the past, current and future impacts of human activities on the biosphere
Paul Crutzen Interview, freeview video ofPaul Crutzen Nobel Laureate for his work on decomposition of ozone talking to Harry Kroto Nobel Laureate by the Vega Science Trust.
