52 Habitats Then and Now-High

Habitats Then and Now FOCUS Question How does the fossil record help us understand how Earth has changed over time?

栖息地过去和现在焦点问题化石记录如何帮助我们了解地球是如何随着时间而变化的?

The Changing Earth Throughout Earth's history, habitats have changed a great deal. Some changes happen quickly. When beavers build dams, they change their habitat. We can see the difference in just a few weeks. Other changes happen very slowly, over thousands or millions of years. In some places, an ocean became a desert and a rainforest became frozen tundra. How do we know these changes have occurred? Fossils— the remains of living things preserved in rock— show us the plants and animals that lived long ago. Fossils also show us how the environment has changed over time. This evidence is part of the fossil record.

不断变化的地球纵观地球的历史，栖息地发生了很大的变化。 有些变化发生得很快。 当海狸建水坝时，它们改变了栖息地。 我们可以在短短几周内看到差异。 其他变化发生得非常缓慢，需要数千年或数百万年。 在一些地方，海洋变成了沙漠，雨林变成了冻土带。 我们如何知道这些变化已经发生? 化石——保存在岩石中的生物遗骸——向我们展示了很久以前生活的植物和动物。 化石还向我们展示了环境是如何随着时间而变化的。 这些证据是化石记录的一部分。

Time Recorded in Rocks Fossils are often found buried deep in rocks. Rock is laid down over time in layers. In places where the layers are undisturbed, younger rock layers rest upon older rock layers. This is called the law of superposition. One way scientists can learn the age of fossils is by studying the rock layer in which they are found. Fossils found in deeper layers come from plants and animals that lived further in the past. The types of fossils in each rock layer provide clues about how a fossil organism's habitat has changed over time. Word Wise Super means "over," and position means "to place." Superposition occurs when new rock layers are naturally placed over old ones.

化石常被发现深埋在岩石中。 岩石随着时间的推移而成层沉积。 在岩层未受扰动的地方，年轻的岩层依附在古老的岩层上。 这就是所谓的叠加定律。 科学家们了解化石年龄的一种方法是研究化石所在的岩层。 在更深的地层中发现的化石来自于生活在更久远年代的植物和动物。 每个岩层中的化石类型为化石生物的栖息地如何随时间变化提供了线索。 Word Wise Super的意思是“结束”，position的意思是“放置”。 当新的岩层自然地覆盖在旧的岩层上时，就会发生叠加。

A Grand Process The Grand Canyon provides an example of the law of superposition. The canyon is over 1,600 meters (1 mi.) deep. It has many different layers of rock. Fossils found in these layers are evidence that the environment in and around the canyon has changed over time. More than a billion years ago, the area that is now the Grand Canyon was at the bottom of a sea! Over millions of years, the sea advanced and retreated in this area many times. As the sea advanced, the water left behind layers of limestone. As the water retreated, layers of shale, slate, and mudstone formed.

大峡谷提供了叠加定律的一个例子。 峡谷深度超过1600米(1英里)。 它有许多不同的岩石层。 在这些岩层中发现的化石是峡谷内外环境随时间变化的证据。 10亿多年前，现在的大峡谷位于海底!在数百万年的时间里，海水在这一地区多次进进出出。 海水前进时，留下了一层层的石灰岩。 随着水的后退，形成了页岩、板岩和泥岩层。

Forces inside Earth eventually pushed up an area of this land. A layer of rock from the bottom of a sea was now at the top of tall mountains! This layer is the Kaibab (KY-bab) limestone. The Colorado River began to cut through the uplifted land. As the Grand Canyon formed, older layers of rock became visible. When the Kaibab limestone was forming under the sea, many creatures became fossils within the rock. Fossils of sea lilies, called crinoids, are found in this layer. Brachiopods— animals similar to clams— are also found there. These fossils reveal that millions of years ago, this area was very different. It was under water! Do You Know? The newest rock layer in the Grand Canyon. Kaibab Limestone, is still very old. It was formed even before dinosaurs existed!

地球内部的力量最终推动了这块土地的一部分。 一层来自海底的岩石现在位于高山的顶部!这一层是凯巴布石灰岩。 科罗拉多河开始穿过隆起的土地。 随着大峡谷的形成，古老的岩石层变得清晰可见。 当凯巴布石灰岩在海底形成时，许多生物在岩石中成为化石。 在这一层中发现了海百合的化石，称为海百合。 腕足类动物——类似蛤蜊的动物——也在那里被发现。 这些化石揭示了数百万年前，这片区域与现在大不相同。 它在水下!你知道吗? 大峡谷中最新的岩层。 凯巴布石灰岩，仍然非常古老。 它甚至在恐龙存在之前就已经形成了!

Super Continent The Himalayas (him-ah-LAY-uz) are the world's highest mountain range. Yet people have discovered ammonite fossils there. Ammonites are sea creatures. This means that the rocks that make up Mount Everest were once on the seafloor. About 225 million years ago, all the continents were one big landmass called Pangaea (pan-GEE-uh). As Pangaea broke apart, a new sea was created. The ammonites lived in this sea. One piece of Pangaea became India. It slowly collided with Asia. The impact caused the seafloor to lift up, creating the Himalayas.

喜马拉雅山(him-ah-LAY-uz)是世界上最高的山脉。 然而人们在那里发现了菊石化石。 鹦鹉螺是海洋生物。 这意味着构成珠穆朗玛峰的岩石曾经在海底。 大约2.25亿年前，所有的大陆都是一个叫做泛大陆(pan-GEE-uh)的大大陆。 随着泛大陆的分裂，一片新的海洋形成了。 亚扪人生活在这海中。 盘古大陆的一部分变成了印度。 它慢慢地与亚洲相撞。 撞击导致海底上升，形成了喜马拉雅山脉。