Baked Alaska (based on Nature article, v. 419, September 12, 2002) The warming o

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Baked Alaska

(based on Nature article, v. 419, September 12, 2002)

The warming of the Earth’s climate more than 50 million years ago is as yet unexplained. Now the finger points to the heating of sediment in the Gulf of Alaska as an important source of the greenhouse gas methane.

Between about 58 and 52 million years ago, the Earth’s climate warmed considerably. What was the cause of this unusually long warming trend? Writing in Geology, Hudson and Magoon put forward an idea that adds to thinking on the subject.

The marine geological record shows that Earth’s climate has experienced swings of cooling and heating over various timescales. Change over thousands to hundreds of thousands of years seems to be related to orbital variations, but climate trends lasting millions of years have been harder to explain. The interval between 58 and 52 million years ago has attracted particular interest, not only because of the exceptional warming but also because this was a time of widespread and intense tectonic activity at the Earth’s surface.

Attempts to find out whether the two are connected have usually centered on the release of greenhouse gases, especially carbon dioxide, generated by tectonic activity. In some models, the CO2 produced is related to volcanism, especially in the northeast Atlantic. In others, the suggestion is that CO2 was released from limestones originally deposited on the northern coast of the Indian subcontinent, which were buried, heated, and then emitted CO2 on a large scale when this land mass collided with the rest of Asia.

Hudson and Magoon propose an alternative tectonic trigger for the global warming of this period, one that invokes methane, not CO2 as the key greenhouse gas. Their model deals with the Gulf of Alaska where they suggest that large volumes of sediment, eroded from freshly uplifted mountains, were deposited in the deep water off the coast of Alaska. In this region, the oceanic Pacific plate is subducting below the Alaskan continent, but the overlying sediments are scraped off forming an accretion prism. As sediment becomes buried and granite pushes up into the sedimentary layer, the heat leads to the production of hydrocarbons (oil and gas), including methane. The large volumes of methane released to the atmosphere, increasing greenhouse gas concentrations, might explain the higher global temperatures 58-52 million years ago.

Question 1: True or False: Scientists agree on the cause of global temperature 58-52 million years ago

Question 2: From the above article, the statement "mehtane release caused global warming about 50 million years ago is an:

a. fact

b.theory

c.hypothesis

d. observation

Question 3: From the above article, what is significant about the time between 58-52 million years ago?

a. more energy was released from the sun, causing significantly warmer climate

b. this period saw both warming and intense tectonic activity

c. dinosaurs became extint at the time

d. tectonic activity caused intense warming

Question 4: From the above article, Hudson and Magoon hypthesized that:

a. Limestones released large volumes of CO2 during the india- asia collision, leading to global warming

b. Volcanoes in Alaska released large volumes of co2 from their vents, causing global warming

c. granite inruded into sediments, heating sediments and allowing release of methane, causing global warming

d. large volumes of co2 were released from sediments off the coast of alask 58-52 million years ago causing global warming

Question 5: what was the main question asked in the above article?

a. what greenhouse gasses were realsed about 50 million years ago?

b. why were greenhouse gases released about 50 million years ago?

c. why does it take 6 million years for climate to change?

d. what was the cause for the long warming trend that occured about 50 million years ago?

Explanation / Answer

1.The answer is false, according to article, Hudson and Magoon hypothesis might exlplain the cause, but still it is not agreed by scientists

2.The answer is c, it is a hypothesis and they proposed it.

3.The answer is b, during this period there was more warming and intense tectonic activity.

4.The answer is c, they explained it based on sediments with granite intruded in it.

5.The answer is d, cause for long global warming trend that occurred about 50 million years ago was the main question.

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