Microbiologia

Hard rock (or heavy rock) is a loosely defined subgenre of rock music which has its earliest roots in mid-1960s garage rock, blues rock and psychedelic rock. It is typified by a heavy use of distorted electric guitars, bass guitar, drums, and often accompanied with pianos and keyboards.
Hard rock developed into a major form of popular music in the 1970s, with bands such as Led Zeppelin, DeepPurple, Aerosmith, AC/DC, and Van Halen, and reached a commercial peak in the mid to late 1980s. The glam metal of bands like Bon Jovi and Def Leppard and the rawer sounds of Guns N' Roses followed up with great success in the later part of that decade, before losing popularity in the face of grunge. Despite this, many post-grunge bands adopted a hard rock sound and in the 2000s there came arenewed interest in established bands, attempts at a revival, and new hard rock bands that emerged from the garage rock and post-punk revival scenes.
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Definitions
Hard rock is a form of loud, aggressive rock music. The electric guitar is often emphasised, used with distortion and other effects, both as a rhythm instrument using repetitive riffs with a varying degree of complexity, and as a sololead instrument. Drumming characteristically focuses on driving rhythms, strong bass drum and a backbeat on snare, sometimes using cymbals for emphasis. The bass guitar works in conjunction with the drums, occasionally playing riffs, but usually providing a backing for the rhythm and lead guitars. Vocals are often growling, raspy, or involve screaming or wailing, sometimes in a high range, or evenfalsetto voice. Hard rock has sometimes been labelled cock rock for its emphasis on overt masculinity and sexuality and because it has historically been predominately performed and consumed by men: in the case of its audience, particularly white, working-class adolescents.
In the late 1960s the term heavy metal was used interchangeably with hard rock, but gradually began to be used to describemusic played with even more volume and intensity.While hard rock maintained a bluesy rock and roll identity, including some swing in the back beat and riffs that tended to outline chord progressions in their hooks, heavy metal's riffs often functioned as stand-alone melodies and had no swing in them.Heavy metal took on "darker" characteristics after Black Sabbath's breakthrough at the beginningof the 1970s, and in the 1980s it developed a number of sub-genres, often termed extreme metal, which were influenced by hardcore punk, and which further differentiated the two styles. Despite this differentiation, hard rock and heavy metal have existed side by side, with bands frequently standing on the boundary of, or crossing between, the genres.

History
Origins (1960s)
In the mid-1960s,American and in particular British rock bands began to modify rock and roll, adding to the standard genre greater blues influence, harder sounds, heavier guitar riffs, bombastic drumming, and louder vocals. Early forms of hard rock can be heard in The Kingsmen's version of "Louie, Louie" (1963), which made it a garage rock standard, and the songs of rhythm and blues influenced British Invasionacts, including "You Really Got Me" by The Kinks (1964), "My Generation" by The Who (1965) and "(I Can't Get No) Satisfaction" (1965) by The Rolling Stones. From the late 1960s it became common to divide mainstream rock music that emerged from psychedelia into soft and hard rock. Soft rock was often derived from folk rock, using acoustic instruments and putting more emphasis on melody andharmonies. In contrast, hard rock was most often derived from blues-rock and was played louder and with more intensity.
Blues-rock acts that pioneered the sound included Cream, Jimi Hendrix Experience and The Jeff Beck Group. Cream, in songs like "I Feel Free" (1966) combined blues-rock with pop and psychedelia, particularly in the riffs and guitar solos of Eric Clapton. Jimi Hendrix produced a form of...