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What are fossils?
Fossils are the remains of plants or animals. For such remains to be considered fossils, scientists have decided they have to be over 10,000 years old. The word fossil comes from the Latin word “fossilis”, which means, “dig up”. Fossils can be divided into “body fossils” and “trace(痕迹) fossils”. Body fossils are the remains of a plant or animal’s body. Trace fossils are the remains of the activity of an animal, such as footprints, egg shells, and nests.
How are fossils formed?
Some animals were quickly covered after their death by sediment(沉淀物) like earth, mud or sand. Over time, the parts of the animals that didn’t rot (usually the harder parts like bones and teeth) were covered in the newly formed sediment. Then, a lot of chemical changes happened to the animals bodies. Water with minerals(矿物质) went into the bone and took the place of the chemicals in the bone with rock-like minerals. In the end we get a heavy, rock-like copy of the original object - a fossil. There weren’t any changes in size and shape when an object changed into a fossil, but the fossil of a bone doesn’t have any bone in it! It is chemically more like a rock! According to scientists, fossils have been found on every continent(大陆) on Earth.
1．Trace fossils can’t be formed from the ______ of some kind of animals.
| A．footprints | B．nests | C．eggs | D．bodies |
| A．Sunlight | B．Earth | C．Water | D．Air |
| A．heavy | B．big | C．old | D．clean |
| A．scientists think that the fossils may have a history of 100 centuries. |
| B．people haven’t found any fossil on the continent of Africa. |
| C．we can find some real bones in the fossils of a bone. |
| D．there are many kinds of sediment in the fossils. |
| A．an advertisement | B．a medical magazine | C．a science book | D．a notice |
同类型试题
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
