TOEFL Listening Practice: Lecture08

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TOEFL Listening Practice: Lecture08

MP3 – SoundCloud

SOLO ENGLISH · TOEFL Listening Practice: Lecture08

Answer

C
D
D
A
C, D
A, B

Transcript

Professor:	We’re going to travel back in time. Not literally, the school doesn’t have funds for that. Our lesson will focus on 11 thousand years ago, when the world was entering its most recent interglacial period. Interglacial periods, as their name might suggest, is the time when the earth warmed up a bit after the last Ice Age ends, and before the next one begins. Earth’s default climate is actually an Ice Age, and the regular thaws between them has allowed various creatures to evolve and thrive. The last one started 11 thousand years ago, and we’re in an Interglacial period right now.
	Like most things in nature, Interglacial periods have a pattern to them. We’ve studied several that have happened in the past, through the evidence they’ve left behind. We can conclude that within the cycle, carbon dioxide and methane gas is normally trapped within the earth’s crust or under the ocean, but will occasionally peak. For reasons that are not entirely clear, the natural gasses will then fall in concentration once again. When the concentration falls, the earth is no longer as thick an insulating layer of atmosphere, or as dense, rather, and heat will be able to escape into space. This leads to the overall temperature of the world falling, and ice moving to cover the continents and thus, another Ice Age.
	However, in the interglacial period we’re in now, the pattern faltered. The gasses peaked, dipped a little, then started to rise again. This hasn’t happened before. What change happened, that would throw the world’s cycle off-balance?
	The simple answer? Humans.
	The agricultural revolution started, as far back as 11 thousand years ago, cutting down forests to create farmland, and encouraging domesticated animals to forage and create large herds. People would farm their food, instead of hunting for it, and would settle down into one spot instead of roaming nomadically. Settling down in an area can have a huge impact on the local environment.
	Scientists have begun to see agricultural revolution as the kickstarter for the recent shift in the climate cycle. New theories have been posed to suggest humans were having an effect well before that. Still, if you cut down trees, burn the forests for fuels, release the carbon smoke into the air, and don’t replace those forests with more trees elsewhere, you end up with a lot more carbon dioxide in the atmosphere instead of being stored within trees.
	Methane on the other hand, tends to form around wetlands in a thick concentration. The cultivation of certain grains, like rice, result in large-scale artificial wetlands that would not have been produced naturally. These artificial changes to the environment dramatically increase the methane concentration of the atmosphere.
	Agriculture, the spread of its human developing reliance on it, ended up taking place over thousands of years. It likely had a dramatic impact on the composition of the earth’s atmosphere. Not only that, but in the early 1800’s, the Industrial revolution began. Coal was used to power factories, spewing such huge amounts of soot into the air that it would blacken the bricks around it.
	It’s a bit ironic if you think about it. Had humans not established themselves on the planet, we very well could have been heading into a new Ice Age. The world is cooling and glaciers are shifting down across Russia and Canada. Instead, we have a problem with Global Warming. Due to our influence, the “Greenhouse Gasses” like Methane and Carbon dioxide are insulating the globe to the point where important glaciers are melting.
	Back in the 1970’s, scientists were quite puzzled as to why the world wasn’t starting to cool back down. Some people think the warmer climate is better for the world, but I disagree. We are entering uncharted territory now, the cycle of our world’s climate broken. There is a small shift toward solar, hydroelectric and aero energy, but many people don’t think that the change is important, or even real. “This is how it’s always been.”
	Nothing lasts forever. The warmth of our planet should be falling, but it’s not. What impacts do you think continued warming could have on our future? When you come back, we’ll talk about that.