Many factors led to the habitability of Earth. One was the relatively low fraction of water on Earth. Others include the moon, plate tectonics, and Earth's magnetic field. The following introduction primarily focuses on planet formation and pertains to section 5-2.
Scientists use many clues to determine how the solar system formed. One is the composition of meteorites. Lichtenberg recently published a paper in Science in which he stated that meteorites indicate that Earth formed in a wet part of the solar system and that radioactive aluminum 26 dried out the planetesimals that formed Earth.
According to the giant impact hypothesis, a planet the size of Mars crashed into the Earth 30 million years after the formation of the solar system. This dislodged material from the Earth, forming a disk around Earth, which eventually coalesced and formed the moon.
This is the great bifurcation in this course, switching from astronomy to geology and life. The Hadean Eon was the first eon in Earth's history.
Prebiotic molecules must form in a strongly reducing atmosphere. Periods of intense asteroid bombardment of Earth created a strongly reducing atmosphere for one to two million years. This provided a brief window when protocells can form. This may have happened in the Hadean Eon but the most likely time of protocell formation was after the Late Heavy Bombardment at the end of the Hadean Eon.
Circulation in Earth's outer core and mantle cause the magnetic field and plate tectonics, respectively, without both of which, intelligent life would not exist on earth. For example, Mars and Venus do not have significant magnetospheres, and oxygen and water were stripped from their atmosphere by solar radiation.
Studying the atmospheres of Biosphere 2, Venus, and Mars helps us to appreciate Earth's amazing atmosphere. A balance of gases in the atmosphere enables for respiration and photosynthesis and helps maintain a habitable temperature. The mass of the Earth's atmosphere and updrafts causing circulation buffer the planet against wild temperature swings between day and night.
Joe Silk, a famous astrophysicist, interviewed planetary scientist Mario Livio about the specialness of the Earth and solar system. Mario Livio would like to believe that there is nothing special about the earth or solar system. In 2000, Ward and Brownlee wrote a book called Rare Earth in which they argued that intelligent life in the universe is rare. it was controversial at the time, but more and more scientists are beginning to agree with them.
In the beginning of the third age, Moses described the gathering of waters in the lower part of the disk and the formation of dry earth.