Airing differences."Changes in the Air: Variations in atmospheric oxygen have affected evolution in big ways" (SN: 12/17/05,p. 395) raises the question of how oxygen levels have changed over the past 2 centuries, when carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. has been increasing. JOHN MILLS
Sir John Mills, CBE (born Lewis Ernest Watts Mills; 22 February 1908 – 23 April 2005) was a popular Academy Award winning English actor who made more than , DECATUR, ALA. There is a problem in this interesting article. The graph of oxygen content versus time doesn't agree with the text. Specific example: "About 255 million years ago ... the oxygen concentration stood at 30 percent." The graph shows this concentration at about 290 million years ago. Which is correct, graph or text? ALAN SOBEL, EVANSTON, ILL. I have long wondered about giant insects in the Carboniferous period Carboniferous period (kärbənĭf`ərəs), fifth period of the Paleozoic era of geologic time (see Geologic Timescale, table), from 350 to 290 million years ago. . What about barometric ba·rom·e·ter n. 1. An instrument for measuring atmospheric pressure, used especially in weather forecasting. 2. Something that registers or responds to fluctuations; an indicator: pressure? Even with increased oxygen, would such insects be able to fly unless air pressure was higher as well? LINDON DURVIN, RICHMOND, VA. Data gathered during the past decade show that the seasonal variations in the concentration of oxygen mirror those of carbon dioxide. Some discrepancies noted here arose because ancient concentrations of atmospheric oxygen have been estimated by various methods, including isotopic i·so·tope n. One of two or more atoms having the same atomic number but different mass numbers. [iso- + Greek topos, analyses of sediments. Also, the graph depicts new data that hadn't been available to the other scientists cited in the text. Regarding insect flight Insects are the only group of invertebrates to have evolved powered flight. Over the past several million years, flying insects have evolved some remarkable flight characteristics and abilities, superior in many ways to anything created by mankind. , experiments with modern insects suggest that oxygen availability, not air density, is the factor that determines whether insects can fly.--S. PERKINS |
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