Ecology: the Biology of Interactions. 2.15. (Supplement) Venus, Earth, Mars
We can only rejoice that, situated between “frozen” Mars and “feverish” Venus, our native Earth provides quite suitable conditions for life.
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2.14. (supplement) Some stages in the history of terrestrial life
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 2. Biospherology
2.16. (supplement) Search for Life in the Solar System
2.15. (supplement) Venus, Earth, Mars Venus provides us with an example of a planet-wide catastrophe. Carl Sagan It is said that many years ago, a famous newspaper publisher sent a telegram to a renowned astronomer: TELEGRAPH URGENTLY FIVE HUNDRED WORDS IS THERE LIFE ON MARS. The astronomer, feeling a sense of duty, replied: NOBODY KNOWS, NOBODY KNOWS, NOBODY KNOWS... and so on for 250 times. Carl Sagan During the formation of star systems, the matter that forms planets is not distributed uniformly. Planets closer to the star are composed of denser substances. In its initial composition and properties, Earth is similar to its two neighboring planets – Venus and Mars. Mercury also belongs to the terrestrial planets, but this small planet is located so close to the Sun that conditions on its surface have nothing in common with Earth's. Venus is very close to Earth in size, density, and mass. This planet is located closer to the Sun than Earth. The temperature on Venus's surface reaches 480°C, and the pressure is 90 atmospheres! Can life exist under such conditions? Complex life based on familiar chemistry is impossible on the planet's surface. Perhaps one can imagine bacterial life existing in clouds of sulfuric acid at an altitude of 45-60 km above the surface – there, the conditions are somewhat more acceptable. What made the planet, named after the goddess of love, so harsh? An excess of carbon dioxide, which caused a greenhouse effect! Mars looks very similar to Earth from the outside. Fortunately, we can observe its surface. Conditions on Mars are not as harsh, and several Earth stations are operating on its surface. At the same time, it is clear that Mars (or rather, hypothetical Martian life) also had bad luck, though not as much as Venus. The atmospheric pressure on Mars is about 100 times weaker than on Earth; the atmosphere consists of 95.3% carbon dioxide, 2.7% nitrogen, and 1.6% argon. Oxygen is present only in trace amounts. Mars's diameter is about half that of Earth (0.53), and its gravity is 2.5 times weaker. The surface area of Mars is close to the land area of Earth's continents. The temperature on this planet ranges approximately from +25°C to -125°C. Light with a significant proportion of ultraviolet radiation, harmful to life, falls from the sky onto the Martian surface. The duration of a Martian day is close to Earth's: 24 hours, 39 minutes, 35 seconds. For many generations, scientists have searched for signs of life on Mars. Observing its surface through telescopes led to an interesting optical illusion: individual spots merged in the imperfect optics into streaks, and observers sketched a network of canals that supposedly covered Mars. In the late 19th century, many believed that industrious Martians had built a planet-wide canal network to transport water from humid polar regions to arid equatorial areas. One of the first to realize the fallacy of these fantasies was Alfred Russel Wallace, a co-author of Darwin's theory of evolution. His calculations showed that the temperature on the planet's surface is so low and the pressure so small that no liquid water could exist there. In the 20th century, scientists searched for microscopic, not intelligent, life on Mars. To a large extent, the search for life on Mars has come down to the search for water. According to prevailing ideas, Mars was once quite warm and wet. Unfortunately, Mars is smaller than Earth and farther from the Sun. At some point, Mars began to cool catastrophically. The water that formed its oceans now lies as ice reserves beneath the planet's surface, covered by a layer of rock and dust. Evidence for these views is abundant – from geological evidence (rocks that could only have formed in liquid water) or the consequences of water seepage from beneath the surface to traces of ancient oceans. Streaks resembling shorelines have long been observed on the surface of Mars. Astronomers doubted this explanation for their origin, as these lines occurred with changes in altitude – it seemed that the shoreline and the water level were sometimes higher and sometimes lower in different places. However, recent simple explanations have been found for the geological processes that caused the changes in the altitudes of ancient shorelines. Thus, 2 billion years ago, two oceans existed on Mars – the Arabian Ocean and Deuteronilus. At that time, Earth's oceans contained quite complex ecosystems formed by prokaryotes. Has the Martian geological ("areological") record preserved traces of life from that time? Detailed studies of its surface are needed to answer this question. In a meteorite ejected from the surface of Mars, bodies were found that strongly resemble fossilized bacteria. Some changes in Mars's atmosphere (e.g., the detection of trace amounts of ammonia in some areas) can be interpreted as the result of "biomarsochemical" activity of living organisms. In 1976, the American landers Viking-1 and Viking-2 conducted experiments on the surface of Mars to detect signs of life. For example, during these experiments, a soil sample was moistened with broth (water with organic compounds) and heated. The decomposition of organic substances in the broth was registered, but it was impossible to determine whether these reactions were a manifestation of microbial activity or an abiotic process. Debates about life on Mars continue to this day... We can only be glad that, situated between the "frozen" Mars and the "feverish" Venus, our native Earth provides quite habitable conditions for life. Additional materials:
Educational module: Factors determining the temperature on the planet Column: Panspermia - a dead end or a hope?
2.14. (supplement) Some stages in the history of terrestrial life
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 2. Biospherology
2.16. (supplement) Search for Life in the Solar System