Leaves with teeth do better in colder climates because teeth are actually really advantageous in jump-starting growth at the beginning of the growing seasons. In this case, you can see this beautiful fossil leaf here with teeth, and each of the teeth are a little hotbeds of photosynthesis(光合作用), so when that leaf first comes out of the bud, it gets a jump-start on leaves that don't have teeth.

Miller uses this information to find out about the height of the young Rocky Mountains. In a simple but powerful technique, he compares the number of leaves with teeth to those without.

You go to a particular area, and you pick up all the species of leaves that are there from the trees that are growing in that area, and you compare the number of species that have teeth to the number of species that have smooth margins. That gives us some idea of what the temperature is.

So the higher the proportion of plants with jagged edges compared to plants with smooth edges, the colder the temperature of the site. And the colder the temperature, the higher the mountain.

So if you've got into a hot air balloon here today, and you float it straight up into the atmosphere, the temperature will decrease in a very predictable way, and it turns out that for about every mile you go up in the atmosphere, you lose about 20 degrees Fahrenheit. So if we know how temperature changes with elevation, we can back out elevation from those estimates of temperature.

To work out the height of the early mountain, Miller needs to compare samples from two areas, one at the base of the mountain and one at the top. Fossils found at the base of the Rockies near the present-day Denver have an amazing story to tell. These ancient leaves are incredibly similar to plants growing in the tropics today.

So after the Rockies rose, down in the area of Denver, it was sub-tropical and tropical forests, we have palms, and cycads, and canopies like we see in the tropics today. Up here we had a forest that looked probably more like a forest that grows in North or South Carolina on the east coast of the U.S.

By comparing the ancient fossil leaves from the top of the mountain with fossil leaves from the foot of the mountain, Miller has come up with a surprising conclusion.

It turns out that the fossil leaves here are predominantly toothed as compared to those that are in Denver which are predominantly smooth margin. And it turns out the ones in Denver grew in a climate that was about, on average about 75 degrees Fahrenheit, the ones up here grew in a climate that was probably about 50 degrees Fahrenheit. So if we know how temperature changes with elevation, that means that this site, when these fossil leaves were deposited, was about a mile higher than Denver. Today it's only a half mile higher. So 60 million years ago, the mountains would be twice as high as they are today.

小編有約：本期的文章中有許多對比的句子，非常的地道。可以摘抄下來，試著自己寫作文的時候用。不僅僅是優美的文章，同時Daisy也認為它告訴了我們探索真理的一種方法。這種方法叫“比較研究法”，通過對近緣物種的行為進行對比分析，以了解行為適應和進化的重要方法。這是一種科學的研究方法。在學習物理和化生時，會用到這個方法。

課后題目：Daisy提供這三個線索，你來找找看這個答案。A. You've got into a hot air balloon. B.You float it straight up into the atmosphere. C. The temperature will decrease in a very predictable way.

來源:可可英語 http://www.ccdyzl.cn/Article/201110/159217.shtml