Practicing on these TOEFL iBT writing tests helps raise your score in the TOEFL Writing Section. Check the audio transcript and sample essay below. This video is in the series of NEW TOEFL iBT Preparation: https://www.youtube.com/playlist?list=PL2jvSGmpWX1XL96rWU4YASA7GNOE1WhJH
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READING PASSAGE (3 minutes)
According to the nebular hypothesis, between 4 and 5 million years ago, a large cloud of dust and gas collected around the region in which the current solar system is positioned. Although similar clouds of dust and gas referred to as nebulae are relatively common and may be found throughout the galaxy, in this cloud as much as 99 percent of the material consisted of hydrogen and helium] and all other naturally occurring elements were also included in small proportions.
Gravity initiated a collapse in the cloud, which in turn caused it to spin rapidly. This spinning resulted in a disk shape with a rounded middle and flat edges. Random regions exerted a stronger gravitational pull and solid elements began to connect and, ultimately, to break apart into small objects called planetesimals ranging in size from a few feet to a few miles. As these planetesimals collided and captured each other, distinct masses concentrated in areas approximately where the planets are now found.
At the same time that the planets were forming, the Sun began to transform itself into a star. The star, which had retained almost 99 percent of the nebula’s original mass, radiated light and heat. The planets nearest the center, which we call the terrestrial planets, were formed from materials that did not disintegrate at higher temperatures, whereas the planets farther away, called the Jovian planets, contained virtually the same mix of helium, hydrogen, and trace elements as the original nebula and were able to condense at much lower temperatures. Asteroids and comets were also swirling around the system, including matter that was not collected by collision with a planet or the gravitational pull of a planet. The fact that the orbits of all the planets lie near the same plane is further evidence of the solar system’s rapid rotation when the nebular cloud began to flatten out.
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AUDIO TRANSCRIPT OF THE LECTURE
Newer high-speed computers have allowed us to perform experiments by modeling events that would be very difficult to duplicate under natural conditions. And we have been able to do some interesting research with models of the collapse of an interstellar cloud under the influence of its own gravitational pull. The modeling has led to a general consensus that stars form in that way—a process of collapse, I mean. So, although the experiments are not definitive, they lead us to the logical conclusion that when a star is born, it will probably have a circum-stellar nebula with conditions that are very favorable to the formation of planets. In effect, we have been able to watch the conditions that existed at the beginning of the formation of the solar system, and observe how the planets were formed. And that’s pretty amazing. Furthermore, the modeling suggests that the planetary formation seems to be a natural consequence of the process that initiates the formation of a star. So, this suggests that planetary systems are the rule, rather than the exception. And that means that an organized search for other planetary systems should yield some rather interesting results. We may find that the nebular hypothesis is valid not only for our solar system but also for other systems in the universe. Besides that, when we do the math, we have to assume that at least some of the stars would produce solar systems with planets that could support life.
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SAMPLE ESSAY
“The nebular hypothesis posits that between four and five million years ago a cloud of dust and gas containing all of the elements in the solar system collapsed under the force of gravity, an event which caused the cloud to spin and flatten into a disk. Then, a stronger gravitational pull caused bodies to merge and pull apart, forming planetesimals that eventually shaped the planets that exist today.
The planets near the Sun, which we call the terrestrial planets, tolerated higher temperatures, but the planets farther away had a composition more similar to the original cloud and condensed when exposed to the lower temperature. The fact that the planets orbit close to the same plane is evidence for the hypothesis.
Furthermore, new technologies have allowed us to test the hypothesis with a computer model, which replicates the original conditions. According to scientists, the formation of planets is a natural result of the process that occurs in the formation of a star. Moreover, the nebular hypothesis suggests that there are other solar systems in the universe, some of which could support life.”
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