<P> Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments . These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrophs, which utilize solar energy . Chemotrophs can be either autotrophic or heterotrophic . Chemotrophs are commonly found in ocean floors where sunlight cannot reach them because they are not dependent on solar energy . Ocean floors often contain underwater volcanos that can provide heat as a substitute for sunlight's warmth . </P> <P> Chemoautotrophs (or chemotrophic autotroph) (Greek: Chemo (χημία) = chemical, auto (αὐτός) = self, troph (τροφιά) = nourishment), in addition to deriving energy from chemical reactions, synthesize all necessary organic compounds from carbon dioxide . Chemoautotrophs use inorganic energy sources such as hydrogen sulfide, elemental sulfur, ferrous iron, molecular hydrogen, and ammonia . Most chemoautotrophs are extremophiles, bacteria or archaea that live in hostile environments (such as deep sea vents) and are the primary producers in such ecosystems . Chemoautotrophs generally fall into several groups: methanogens, halophiles, sulfur oxidizers and reducers, nitrifiers, anammox bacteria, and thermoacidophiles . An example of one of these prokaryotes would be Sulfolobus . Chemolithotrophic growth can be dramatically fast, such as Hydrogenovibrio crunogenus with a doubling time around one hour . </P> <P> The term "chemosynthesis", coined in 1897 by Wilhelm Pfeffer, originally was defined as the energy production by oxidation of inorganic substances in association with autotrophy - what would be named today as chemolithoautotrophy . Later, the term would include also the chemoorganoautotrophy, that is, it can be seen as a synonym of chemoautotrophy . </P> <P> Chemoheterotrophs (or chemotrophic heterotrophs) (Gr: Chemo (χημία) = chemical, hetero (ἕτερος) = (an) other, troph (τροφιά) = nourishment) are unable to fix carbon to form their own organic compounds . Chemoheterotrophs can be chemolithoheterotrophs, utilizing inorganic energy sources such as sulfur or chemoorganoheterotrophs, utilizing organic energy sources such as carbohydrates, lipids, and proteins . Most animals and fungi are examples of chemoheterotrophs . </P>

The first autotrophs which were chemoautotrophs emerged where