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Listen to an Academic Talk Test #044
Listen to an Academic Talk
1. What is the lecture mainly about?
A) The chemical composition of desert rocks
B) Methods for dating geological formations
C) How certain types of ancient rock art were made
D) The discovery of important archaeological sites
2. According to the professor, what is desert varnish?
A) The lighter-colored rock found under a surface
B) A tool used by ancient people to carve images
C) A dark coating that forms on rock surfaces
D) A type of paint used to create rock art
3. What does the professor imply about the rock located under desert varnish?
A) It is darker than the varnish itself.
B) It is the same color as the varnish.
C) It is lighter in color than the varnish.
D) It is too soft to be carved.
4. Why does the professor mention that petroglyphs are fragile?
A) To explain why they are difficult to find
B) To suggest that few of them were ever created
C) To emphasize the need for their preservation
D) To argue that they were not meant to be permanent
Professor: Today we'll discuss a unique intersection of geology and human history: petroglyphs. These are ancient images created by removing part of a rock's surface by carving or scraping. They are essentially rock art.
The creation and visibility of many petroglyphs rely on a geological feature called desert varnish. This is a thin, dark-colored coating, almost like a stain, that forms on the surface of rocks in arid environments over many thousands of years. It's primarily made of clay minerals, along with manganese and iron oxides.
Ancient artists discovered that by chipping away this dark desert varnish, they could expose the much lighter, unweathered rock underneath. This created a striking visual contrast, making the image stand out clearly. The age of a petroglyph can sometimes be estimated by how much varnish has started to re-form over the carved area. Unfortunately, this makes these cultural artifacts very fragile and susceptible to erosion and other damage.
The creation and visibility of many petroglyphs rely on a geological feature called desert varnish. This is a thin, dark-colored coating, almost like a stain, that forms on the surface of rocks in arid environments over many thousands of years. It's primarily made of clay minerals, along with manganese and iron oxides.
Ancient artists discovered that by chipping away this dark desert varnish, they could expose the much lighter, unweathered rock underneath. This created a striking visual contrast, making the image stand out clearly. The age of a petroglyph can sometimes be estimated by how much varnish has started to re-form over the carved area. Unfortunately, this makes these cultural artifacts very fragile and susceptible to erosion and other damage.
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