kristi obrien's Profile

Among his readings was an essay by an economist named Thomas Malthus.  Malthus noticed that a growing population could become so large that food would become scarce. That meant that not everybody who was born could survive to grow up and have children. Darwin realized that what was true for people would also be true for animals and even plants. Without enough food (or other resources) to go around, some individuals would live, others would die.

That insight helped Darwin solve a problem he had been thinking about. Most scientists in his day thought that all of the species of life on Earth had always remained the same. But during his Beagle voyage, Darwin began to wonder.

The strange plants and animals and fossils he had seen showed that many forms of life were similar — but also slightly different. In the struggle to survive in a world of scarce resources, maybe the slightest difference would be helpful.  Animals or plants with helpful differences would be the most likely to survive and pass along those differences to their offspring. Organisms with unhelpful differences would be more likely to die before they had offspring.

It is perhaps not so odd that the idea of Martian canals was so readily accepted by many. At the time, in the late 19th century, telescopic observers had difficulty distinguishing exactly what they were seeing when they looked at Mars (indeed, it was not until the era of space probes that a clear picture emerged). They saw some lighter or darker albedo features (for instance Syrtis Major) and believed that they were seeing oceans and continents. They also believed that Mars had a relatively substantial atmosphere. They knew that the rotation period of Mars (the length of its day) was almost the same as Earth's, and they knew that Mars' axial tilt was also almost the same as Earth's, which meant it had seasons in the astronomical and meteorological sense. They could also see Mars' polar ice caps shrinking and growing with these changing seasons. It was only when they interpreted changes in surface features as being due to the seasonal growth of plants that life was hypothesized by them (in fact, Martian dust storms are responsible for some of this). By the late 1920s, however, it was known that Mars was very dry and had a very low atmospheric pressure.

In addition, the late 19th century was a time of great canal building on Earth. For instance, the Suez Canal was completed in 1869, and the abortive French attempt to build the Panama Canal began in 1880. It is perhaps natural that some thought similar projects were being undertaken on Mars. In 1889, astronomer Charles A. Young reported that Schiaparelli's canal discovery of 1877 had been confirmed in 1881, though new canals had appeared where there hadn't been any before, prompting "very important and perplexing" questions as to their origin.^[9]

For a time in the late 19th and early 20th centuries, it was believed that there were canals on Mars. These were a network of long straight lines that appeared in drawings of the planet Mars in the equatorial regions from 60° N. to 60° S. Lat., first observed by the Italian astronomer Giovanni Schiaparelli during the opposition of 1877, and confirmed by later observers. Schiaparelli called these canali, which was translated into English as "canals" (see below). The Irish astronomer Charles E. Burton made some of the earliest drawings of straight-line features on Mars, although his drawings did not match Schiaparelli's.






Contents [hide] 1 Controversy 2 History of canals 3 Fiction 4 List of canals 5 See also 6 References 7 External links


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[edit] Controversy











Mars as seen through 6 inch (15 cm) aperture reflecting telescope in small telescope in 2003.







Some people went so far as to propose the idea that the canals were irrigation canals built by a supposed intelligent civilization on Mars. Percival Lowell was a strong proponent of this view, pushing the idea much further than Schiaparelli, who for his part considered much of the detail on Lowell's drawings to be imaginary. Some observers drew maps in which dozens if not hundreds of canals were shown with an elaborate nomenclature for all of them. Some observers saw a phenomenon they called "gemination", or doubling - two parallel canals.




Other observers disputed the notion of canals. The gifted observer E. E. Barnard did not see them. In 1903, Joseph Edward Evans and Edward Maunder conducted visual experiments using schoolboy volunteers that demonstrated how the canals could arise as an optical illusion,^[1] since when a poor quality telescope views an object with many point-like features (e.g. sunspots or craters) they 'appear' to join up to form lines.^[2] In 1907 the British naturalist Alfred Russel Wallace published the book Is Mars Habitable? that severely criticized Lowell's claims. Wallace's analysis showed that the surface of Mars was almost certainly much colder than Lowell had estimated, that the atmospheric pressure was too low for liquid water to exist on the surface, and he pointed out that several recent efforts to find evidence of water vapor in the Martian atmosphere with spectroscopic analysis had failed. He concluded that complex life was impossible, let alone the planet girding irrigation system claimed by Lowell.^[3] The influential observer Eugène Antoniadi used the 83-cm (32.6 inch) aperture telescope at Meudon Observatory at the 1909 opposition of Mars and saw no canals, and the notion of canals began to fall out of favor. Around this time spectroscopic analysis also began to show that no water was present in the Martian atmosphere.^[2]

It is perhaps not so odd that the idea of Martian canals was so readily accepted by many. At the time, in the late 19th century, telescopic observers had difficulty distinguishing exactly what they were seeing when they looked at Mars (indeed, it was not until the era of space probes that a clear picture emerged). They saw some lighter or darker albedo features (for instance Syrtis Major) and believed that they were seeing oceans and continents. They also believed that Mars had a relatively substantial atmosphere. They knew that the rotation period of Mars (the length of its day) was almost the same as Earth's, and they knew that Mars' axial tilt was also almost the same as Earth's, which meant it had seasons in the astronomical and meteorological sense. They could also see Mars' polar ice caps shrinking and growing with these changing seasons. It was only when they interpreted changes in surface features as being due to the seasonal growth of plants that life was hypothesized by them (in fact, Martian dust storms are responsible for some of this). By the late 1920s, however, it was known that Mars was very dry and had a very low atmospheric pressure.

In addition, the late 19th century was a time of great canal building on Earth. For instance, the Suez Canal was completed in 1869, and the abortive French attempt to build the Panama Canal began in 1880. It is perhaps natural that some thought similar projects were being undertaken on Mars. In 1889, astronomer Charles A. Young reported that Schiaparelli's canal discovery of 1877 had been confirmed in 1881, though new canals had appeared where there hadn't been any before, prompting "very important and perplexing" questions as to their origin.^[9]