Around 200 million years ago, the earth was 18 degrees warmer than it is now. That might be a bit hot for humans, but it was just right for the giant dinosaurs that wandered about the earth during the Mesozoic (中生代的) era. A new study found that planteating dinosaurs may have contributed to the warming of the earthby releasing significant amounts of methane (甲烷)．
The study, published in science journal Current Biology, focused on sauropods, longnecked herbivores (食草动物) that munched (用力咀嚼) on the top of trees. They were the largest of the dinosaurs; food broke down in their stomachs for long periods of time. The researchers estimate that a sauropoda released 2,675 liters of methane per day—adding up to a large amount of the greenhouse gas being pumped from dinosaur's gut into the atmosphere.
Plant eaters naturally release methane as part of their digestive process. The larger the animal, the more methane it produces. Methane, a greenhouse gas, traps heat and remains in the atmosphere for approximately 915 years, which warms the atmosphere.
Today, some animals, such as cattle, goats and sheep, produce large amounts of methane as a byproduct to their food digestion. Methane is also released from human—influenced sources such as landfill, agricultural activities, coal mining and other industrial practices—which all contribute to today's climate change, according to the Environmental Protection Agency.
The researchers estimate that earth's sauropods would have produced about 520 million tons of methane per year—similar to the total amount of methane produced today by natural and manmade sources. However, the researchers warn that their numbers are estimates based on multiple assumptions about the digestive systems and populations of dinosaurs.
The author of the study David Wilkinson says the emission of methane from dinosaurs would have been just one of the causes of warm climate during the Mesozoic era. Other causes include gases produced from volcanoes, swamps, shallow seas and so on. Still, Wilkinson says，“ The amount of methane from dinosaurs is large enough to have a measurable effect.”
1.Scientists think dinosaurs may have led to the global warming because ________.
A．they ate everything they found
B．they usually had a good appetite
C．they released a lot of methane
D. there were too many dinosaurs on earth
2.What do we know about dinosaurs from Paragraph 2?
A．Sauropods fed on plants.
B．Sauropods were of medium size.
C．Dinosaurs used to live on trees.
D．Dinosaurs digested food quickly.
3.Which of the following activities doesn't produce methane?
A．Coal is dug out by machine.
B．Trees and flowers are planted.
C．Goats digest grass under the tree.
D．Food is being processed in the factory.
4.How does the author make his writing reliable?
A．By listing some facts.
B．By making predictions.
C．By citing figures.
D．By using mind pictures.
5.David Wilkinson seems to believe that ________.
A．methane had little effects on the earth
B．many other factors contributed to warm climate
C．other causes for warm climate were worth considering
D．dinosaurs were mainly to blame for global warming
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