Subject: The Environment

Ages: 10+; Elementary – High School;

Length: Film Clip: 16 minutes, 15 seconds; Lesson: 40 minutes, depending upon the extent to which the supplementary materials are discussed with the class.

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Students will be introduced to some of the world’s most interesting and beautiful caves and to their strange inhabitants, extremophiles and troglobites. Students will be introduced to the different types of extremophiles and the terms scientists use to describe them.


Caves are an important geological feature seldom directly experienced by people living in modern cultures. Extremophiles and troglobites are examples of the tremendous adaptability of life.


This is a portion of the Planet Earth chapter on caves.


Troglobites are animals adapted to living their entire lives beyond the daylight zone of caves. Eyeless spiders, translucent millipedes, cave crickets, and 175-year-old crayfish are examples of troglobites. Many have improved senses of smell, taste, temperature, hearing, and vibration detection. Often amped-up nerve centers for these senses make up for the lack of sight. Other troglobites possess extraordinarily long legs with spiky feet adapted to stick to the moist surfaces of rocks. Some troglobites are exclusive to only one or a few cave systems and have adapted to those particular environments. Some troglobites have super-slow metabolisms that allow them to survive for months without food in dark stagnant caves.

The word troglobite comes from the Greek word “trogle” which means hole or cave. It used to be “trogloboint” but was influenced by the word “troglodyte” which means a person who lives in a cave.

About 8000 cave-dwelling species have been catalogued by scientists. This is only a small part of what lives below.

The Cueva de Villa Luz (Cave of the Lighted House), also called the Villa Luz cave and featured in the movie, is located near Tapijulapa in southern Mexico near the Yucatan Peninsula.

Lechuguilla Cave, also shown in the film, is located near Carlsbad, New Mexico and features unusual geology and rock formations. With a length of 126 miles, it is the fifth longest cave in the world. The cave is named after the Agave Lechuguilla plant which is found near its entrance.

As scientists explored the Lechuguilla cave, they were greeted with more than just a massive cave structure. Large amounts of gypsum and bright yellow sulfur deposits line the walls and make chandelier-like formations that sparkle with beauty. In Lechuguilla, the profusion of gypsum and sulfur supports speleogenesis (the formation of caves and the structures found within them) by the dissolution of sulfuric acid. These caverns apparently formed from the bottom up due to this process.

Very rare, chemolithoautotrophic bacteria which feeds on sulfur, iron and manganese, can be found in the Lechuguilla cave. Since no light penetrates the recesses of a cave, these bacteria do not use photosynthesis as a way to obtain energy. They may assist in enlarging the cave and etching the shapes of some of the cave’s unusual speleothems (mineral deposits formed in caves, such as stalactites or stalagmites). Lechuguilla is the fifth longest cave structure known to mankind and the third longest in the United States. It is the deepest limestone cave in the country.




“Our kind of life, that is life made with carbon compounds floating in water, does have some absolute constraints based on the nature of our chemistry. The boiling and freezing points of water, acid and alkaline extremes, the presence or absence of oxygen, and other factors provide the physical window frame within which life can expand.” Dr. Penelope Boston, Ph.D.


Extremophiles are organisms that thrive in physically or geochemically extreme conditions that are harmful to the majority of life on earth. These creatures can be found in areas that may be extraordinarily hot, cold, dry, or under immense pressure. Some scientific theories contend that life on earth began in these extreme conditions, such as heat vents far under the ocean’s surface.

Most known extremophiles are microbes. However, a few extremophiles are multicellular, including the Pompeii worm, the Psychophysics Grylloblattodea (an insect) and the Antarctic Krill.


Extremophiles are classified by the harsh conditions to which they adapt. Examples are:

acidophilic — optimal growth between pH 1 and pH 5 — Volcanic environments such as sulfur springs and hot pots are home to acidophilic bacteria.

alkaliphilic — optimal growth above pH 9; Antarctica’s Lake Untersee in which the water brims with methane and has an alkaline pH comparable to bleach;

barophilic — organisms that grow under high barometric pressure — The bottom of the sea or far below the Earth’s surface are examples of environments with extreme high pressure. Deep subsurface bacteria grow at 50 – 500 meters below the Earth’s surface.

halophilic — environments that are much saltier than sea water — Salt flats or inland seas, such as Utah’s Great Salt Lake, or deep in the ocean where salinity increases, are examples of environments for these organisms.

thermophilic — optimal growth between 60 and 80º C (between 140 and 176º F) — Organisms that live close to volcanos or volcanic activity are examples of thermophilic extremophiles.

hyperthermophilic — optimal growth above 80º C (above 176º F) — These are organisms that live even closer to volcanos or volcanic vents than do thermophiles.

psychrophilic — optimal growth at low temperatures, usually 15º C (60º F), or lower until 0º C (32º F) the freezing point of water — Organisms that live in the Arctic or the Antarctic, on the surface, encased in ice or floating in water are examples of psychrophilic extremophiles.

oligotrophic — growth in environments with very scarce food sources — Caves, deserts, high mountains, or very cold environments are homes to this type of extremophile.

endolithic — growth within rock or within pores of mineral grains.

xerophilic — growth in dry conditions, with very low water availability — Examples are organisms that live in deserts or dried up lake beds or streams. Many organisms will go into a suspended state during dry weather or, like some frogs, wrap themselves in mud balls at the bottom of dry lake beds, only to revive, feed, mate and give birth, in the short periods when the rains come.

polyextremophile — organisms that adapt to multiple extreme environments — Examples include thermoacidophiles (hot and acidic environments) and haloalkaliphiles (salty alkoline environments). Places in which polyextremophiles grow include the anoxic brine lakes at the bottom of the Mediteranean Sea near Sicily in which the salinity is 10 times greater than normal sea water, pressures are 400 times greater than the atmospheric pressure at sea level, and there is very little oxygen.

toxitolerant extremophiles — organisms that do well in highly toxic conditions — The radiation-charged area around the Chernobyl nuclear disaster site is an example of the type of environment in which these extremophiles will flourish. Finding or developing toxitolerant extremophiles is a way help clean up polluted and toxic environments.

Octopus Spring is a crystal blue alkaline hot spring in Yellowstone National Park. It drains through radiating channels that look like the arms of an octopus. The spring steadily discharges between 75 to 100 gallons a minute. At the source, the water is about 95º C, very close to the boiling point of water. In the outflow channels it cools to a low of about 83º C. These channels flow into an extensive and colorful growth of microbial mats. Pink filamentous communities appear in the channels about two meters from the crystal blue pool. As temperatures decrease, the microbial communities change.

Many scientists believe that early conditions on Earth were very extreme and that the first living organisms were extremophiles. Thus, the study of extremophiles can provide clues to the origins of life. The Earth is just a small part of the universe. Most of space and the other planets have conditions of extreme heat and cold. Few have the blanket of nitrogen/oxygen atmosphere that protects the Earth and fosters carbon-based life.


Origins of the Names Given to Extremophiles


The names given to types of extremophiles are an excellent way to demonstrate how scientists coin words to describe what they see in nature.

The root word for most extremophile types is “phile” from the Greek word “philia” meaning love. Some of the prefixes are obvious, such as “acid” or “alkali” (for alkaline). The prefix in barophilic comes from “bar” a unit for measuring pressure as in “barometric pressure”. This was derived from the Greek word “baros” which means weight. The prefix in halophilic comes from the Greek word “halo” meaning salt. The prefix in thermophilic comes from the Greek word “therm” which means heat. The “hyper” in hyperthermophilic comes from the Greek and means above, over, or excessive. The prefix “xer” means dry and xerophilic extremophiles are organisms that can thrive in very dry conditions. Finally, the prefix “poly” means many. A polyextremophile is an organism that lives in more than one extreme environment.

“Oligo” is the Greek word for few and the word “trophic” means of or relating to nutrition. Oligotrophic extremophiles are organisms that live in environments in which there is little food.

The “endo” in endolithic comes from the Greek word meaning within or inside and the root word, “lithic” means of or pertaining to rock.

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Troglobites: Have students research and report on the adaptations to their environment of a species of troglobite. The Cave Angel Fish, the Texas Cave Salamander and the Belizean White Crab are among the troglobites featured in this snippet. The report can be an essay or a class presentation.


Extremophiles: Students can be asked to report to the class or to write a description of a species of extremophile or to report on such a species to the class.


Extremophiles: Students can be asked to write or to report to the class a description of new advances in the use of extremophiles to clean up hazardous wastes.


Famous Caves: Students can research and either report or write about famous caves featured in the movie or about famous caves not mentioned in the “Planet Earth” snippet.


This Snippet Lesson Plan was written by James Frieden and Justin Frieden. Last revised on September 11, 2009.

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