Answer:
C) Oxygen
Explanation:
As the Earth cooled, a primitive atmosphere was created by the out-gassing of early volcanoes. The early atmosphere contained no oxygen and would have been toxic to human beings, as well as most other life on Earth today.
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Answer:
RNA is formed by a single strand of nucleotides and not a double helix like DNA; RNA, as a protein, but not as DNA, can catalyze important biological reactions. The RNA molecules that function as enzyme proteins are called ribozymes.
Explanation:
From our perspective on Earth, two types of eclipses occur: lunar, the blocking of the Moon by Earth's shadow, and solar, the obstruction of the Sun by the Moon.
When the Moon passes between Sun and Earth, the lunar shadow is seen as a solar eclipse on Earth. When Earth passes directly between Sun and Moon, its shadow creates a lunar eclipse.
Lunar eclipses can only happen when the Moon is opposite the Sun in the sky, a monthly occurrence we know as a full Moon. But lunar eclipses do not occur every month because the Moon's orbit is tilted five degrees from Earth's orbit around the Sun. Without the tilt, lunar eclipses would occur every month.
Lunar and solar eclipses occur with about equal frequency. Lunar eclipses are more widely visible because Earth casts a much larger shadow on the Moon during a lunar eclipse than the Moon casts on Earth during a solar eclipse. As a result, you are more likely to see a lunar eclipse than a solar eclipse.
A balance is used for measuring mass.
