From Perupedia They are created by carving, etching, incising, rubbing, and pounding the rock surface to create images. The word comes from the Greek words petros meaning "stone" and glyphein meaning "to carve" (it was originally coined in French as pétroglyphe).
The term petroglyph should not be confused with pictograph, which is an image drawn or painted on a rock face. Both types of image belong to the wider and more general category of rock art. Petroforms, or patterns and shapes made by many large rocks and boulders over the ground, are also quite different.
The oldest petroglyphs are dated to approximately the Neolithic and late Upper Paleolithic boundary, about 10,000 to 12,000 years ago, if not earlier (Kamyana Mohyla). Around 7,000 to 9,000 years ago, other precursors of writing systems, such as pictographs and ideograms, began to appear. Petroglyphs were still common though, and some cultures continued using them much longer, even until contact with Western culture was made in the 20th century. Petroglyphs have been found in all parts of the globe except Antarctica with highest concentrations in parts of Africa, Scandinavia, Siberia, southwestern North America, and Australia.
There are many theories to explain their purpose, depending on their location, age, and the type of image. Some petroglyphs are thought to be astronomical markers, maps, and other forms of symbolic communication, including a form of pre-writing. Petroglyph maps may show trails, symbols communicating time and distances traveled, as well as the local terrain in the form of rivers, landforms and other geographic features. A petroglyph that represents a landform or the surrounding terrain is known as a Geocontourglyph. They might also have been a by-product of other rituals: sites in India, for example, have been identified as musical instruments or "rock gongs". 
Some petroglyph images probably had deep cultural and religious significance for the societies that created them; in many cases this significance remains for their descendants. Many petroglyphs are thought to represent some kind of not-yet-fully understood symbolic or ritual language. Later glyphs from the Nordic Bronze Age in Scandinavia seem to refer to some form of territorial boundary between tribes, in addition to possible religious meanings. It also appears that local or regional dialects from similar or neighboring peoples exist. The Siberian inscriptions almost look like some early form of runes, although there is not thought to be any relationship between them. They are not yet well understood.
Some researchers have noticed the resemblance of different styles of petroglyphs across different continents; while it is expected that all people would be inspired by their surroundings, it is harder to explain the common styles. This could be mere coincidence, an indication that certain groups of people migrated widely from some initial common area, or indication of a common origin. In 1853 George Tate read a paper to the Berwick Naturalists' Club at which a Mr. John Collingwood Bruce agreed that the carvings had "... a common origin, and indicate a symbolic meaning, representing some popular thought."  In his cataloguing of Scottish rock art, Ronald Morris summarized 104 different theories on their interpretation. .
Other, more controversial, explanations are grounded in Jungian psychology and the views of Mircea Eliade. According to these theories it is possible that the similarity of petroglyphs (and other atavistic or archetypal symbols) from different cultures and continents is a result of the genetically inherited structure of the human brain.
Other theories suggest that petroglyphs were made by shamans in an altered state of consciousness, perhaps induced by the use of natural hallucinogens. Many of the geometric patterns (known as form constants) which recur in petroglyphs and cave paintings have been shown Template:By whom to be "hard-wired" into the human brain; they frequently occur in visual disturbances and hallucinations brought on by drugs, migraine and other stimuli.
Petroglyphs in Peru
- Toro Muerto Petroglyphs
- Checta Petroglyphs
- Chichictara Petroglyphs
- Petroglyphs of Polish
- Petroglyph of the Mollepunco Caves
- Miculla Petroglyphs
- Chiquian Petroglyphs
- Huancor Petroglyphs
- ↑ http://www.thefreedictionary.com/petroglyph
- ↑ http://archaeology.about.com/od/pterms/g/petroglyphs.htm
- ↑ http://www.wordiq.com/definition/Petroglyph
- ↑ Ancient Indians made 'rock music', BBC News Friday, 19 March, 2004
- ↑ J. Collingwood Bruce (1868; cited in Beckensall, S., Northumberland's Prehistoric Rock Carvings: A Mystery Explained. Pendulum Publications, Rothbury, Northumberland. 1983:19)
- ↑ Ronald Morris, The Prehistoric Rock Art of Galloway and The Isle of Man (ISBN 978-0-7137-0974-2 , Blandford Press 1979
- ↑ [see Lewis-Williams, D. 2002. A Cosmos in Stone: Interpreting Religion and Society through Rock Art. Altamira Press, Walnut Creek, Ca.]