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- Season 0 1966-12-25
- Season 1 1964-02-04
- Season 2 1965-01-06
- Season 3 1966-01-02
- Season 4 1967-01-17
- Season 5 1968-01-02
- Season 6 1969-01-02
- Season 7 1970-01-05
- Season 8 1971-01-04
- Season 9 1972-01-03
- Season 10 1973-01-04
- Season 11 1974-01-07
- Season 12 1975-01-20
- Season 13 1976-01-05
- Season 14 1977-01-07
- Season 15 1978-01-06
- Season 16 1979-02-26
- Season 17 1980-01-14
- Season 18 1981-01-05
- Season 19 1982-01-11
- Season 20 1983-01-10
- Season 21 1984-01-09
- Season 22 1985-01-07
- Season 23 1986-01-06
- Season 24 1987-01-05
- Season 25 1988-01-04
- Season 26 1989-01-09
- Season 27 1990-01-08
- Season 28 1991-01-07
- Season 29 1992-01-06
- Season 30 1993-01-04
- Season 31 1994-01-10
- Season 32 1995-01-09
- Season 33 1996-01-08
- Season 34 1997-02-27
- Season 35 1998-02-19
- Season 36 1999-01-28
- Season 37 2000-01-12
- Season 38 2001-01-25
- Season 39 2002-01-10
- Season 40 2003-01-09
- Season 41 2004-01-08
- Season 42 2005-01-13
- Season 43 2006-01-12
- Season 44 2007-03-13
- Season 45 2008-01-15
- Season 46 2009-01-26
- Season 47 2009-10-13
- Season 48 2010-09-27
- Season 49 2011-08-08
- Season 50 2012-07-23
- Season 51 2013-08-12
- Season 52 2014-08-18
- Season 53 2016-03-16
- Season 54 2017-01-19
- Season 55 2018-02-05
- Season 56 2019-01-23
- Season 57 2020-01-16
- Season 58 2021-01-04
- Season 59 2022-03-31
- Season 60 2024-07-22
Season 60 Episode
- Season 40 The Mystery Of Easter Island
- Season 40 Living Nightmare
- Season 40 Averting Armageddon
- Season 40 Dirty Bomb
- Season 40 Sexual Chemistry (Update)
- Season 40 The Day We Learned To Think
- Season 40 Trial and Error
- Season 40 Earthquake Storms
- Season 40 Life On Mars (Update)
- Season 40 The Secret Life Of Caves
- Season 40 God On The Brain
- Season 40 Flight 587
- Season 40 SARS: The True Story
- Season 40 The Big Chill
- Season 40 The Bible Code
- Season 40 Last Flight of the Columbia
- Season 40 The Hunt for an AIDS Vaccine
- Season 40 Percy Pilcher's Flying Machine
- Season 40 Time Trip
Horizon - Season 40 Episode 10 The Secret Life Of Caves
7.40 60 minutes Set against the back drop of awe inspiring geological beauty, a strange scientific adventure sets out to discover how a mineral clad cave network - the height of a 30 storey building and the length of six football fields - came to exist deep below the Guadalupe Mountains in North America.
But this journey soon unravels a multitude of inexplicable phenomena and obscure geological formations, leading to the discovery of extreme rock-eating microbes - a testimony from primordial Earth and a glimpse of life elsewhere in the Solar System.
Geologists believed that all limestone caves were formed by rain and underground water percolating through cracks in the rocks. Absorbing carbon dioxide from the soil, this water becomes weak carbonic acid, nibbling away at limestone, etching out networks of subterranean caves.
