Why does detection of abundant free oxygen in an atmosphere suggest life is present? Does its absence prove life could not be present?
What will be an ideal response?
Oxygen is highly reactive, and unless quickly replaced by photosynthesis, would soon disappear into surface rocks, as it has on Mars and Venus. However, life on Earth certainly evolved before it released the abundant present oxygen, and on other worlds, photosynthesis may not have evolved. Yet other forms of life may thrive using methane or hydrogen sulfide, all energy processes found here as well.
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As a parcel of air is swept upward, with no heat input or output, its temperature
A) increases. B) decreases. C) remains the same.
The reason an astronaut in an earth satellite feels weightless is that
A) the astronaut is beyond the range of the earth's gravity. B) the astronaut is falling. C) the astronaut is at a point in space where the effects of the moon's gravity and the earth's gravity cancel. D) this is a psychological effect associated with rapid motion. E) the astronaut's acceleration is zero.
A stick is moving along the x-axis at 90%c. A person riding with the stick sees it inclined at 45.° with respect to the x-axis. Observers in the rest frame see the stick making what angle with respect to the x-axis?
A) 79.° B) 66.° C) 53.° D) 45.° E) 88.°
A fusion reaction works because the binding energy of the resulting nucleus
A) is greater than the binding energy of the original nuclei. B) is equal to the binding energy of the original nuclei. C) is less than the binding energy of the original nuclei. D) is released in the process. E) is absorbed in the process.