Fossils Tell Stories
FoundationFossils are the remains or traces of ancient life kept in rocks and ice; from their kinds and positions in strata we can infer past environments and how the surface changed.
- Fossils are ancient remains or traces in rock and ice.
- Most form in sedimentary rock; deeper strata are older.
- Fossil kinds reveal ancient environments.
文體小知識：說明文把遠古的故事翻譯給你聽。這一篇教你讀懂化石，從石頭裏的線索推斷地球的過去。
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1In the museum, a giant set of dinosaur bones stands high on a frame, and every child looks up in wonder. These bones are fossils: the remains and traces left by ancient creatures, turned stone-like over immense ages and kept in rocks, preserving the Earth's oldest memories for us.
2Fossils are not only dinosaur bones. Shells, fish, plant leaves and footprints can all become fossils; some ancient remains were sealed in ice — like the woolly mammoths found in Siberian frozen ground, with hair and skin preserved, as if kept in a natural freezer.
3How do fossils form? When a creature dies and is quickly buried by mud and sand, shut away from air, it does not easily decay. Over tens of millions of years the layers pack into sedimentary rock, and minerals slowly fill and harden the spaces in the remains until they become fossils. That is why most fossils hide in sedimentary rock, and forming one is extremely rare.
4Sedimentary rock is like a great layered book: the deeper the layer, the older it is. A fossil's layer records the age it lived in. By comparing fossils from different strata, scientists can order when ancient creatures appeared and rebuild the timetable of the evolution of life.
5Fossils also tell of changes on the surface. Finding shells or ammonites — sea creatures — in mountain rocks means the place was once ocean, later lifted into land by crustal movement; finding tropical plant fossils in cold regions means the climate there was once very different.
6Fossils are the Earth's diary, page after page recording ancient life and environments. Studying them lets us know the dinosaurs, the mammoths and the evolution of life. Next time you meet a fossil in a museum, look closely and listen to its ancient story.
1Summary 重點摘要
Fossils are the remains or traces of ancient life kept in rocks and ice; from their kinds and positions in strata we can infer past environments and how the surface changed.
2Vocabulary cards Vocabulary
The remains or traces of ancient life kept in rock or ice.
Creatures that lived long ago, most of them now extinct.
The body parts left after death, such as bones and shells.
Rock formed from layers of packed sediment — the common home of fossils.
The layers of rock; the deeper the layer, the older it is.
Thick ice that can keep ancient remains, such as mammoths.
An ancient sea creature whose spiral shell often becomes a fossil.
A giant ancient relative of elephants, found whole in frozen ground.
Drawing a sensible conclusion from evidence, such as reading sea fossils as signs of an ancient ocean.
A scientist who studies fossils and ancient life.
3Step by step Steps
- Step 1: Know what fossils areFossils are the remains or traces left by ancient creatures, turned stone-like over tens of millions of years and kept in rock or ice. Common fossils include bones, shells, teeth, leaves and footprints. Like natural photographs, they preserve what ancient life looked like and tell us who once lived on Earth. Remember: fossils are always linked to ancient life; an ordinary stone with no trace of living things is not a fossil.
- Step 2: See how fossils formFossil formation is very rare. After death, remains must be quickly buried by mud and sand, cut off from air and scavengers, or they rot away. Over the following tens of millions of years the layers pile up and pack into sedimentary rock, and mineral-rich water slowly seeps into, fills and hardens the spaces in the remains until they turn to fossil. Soft parts usually vanish; mostly the hard parts — bones and shells — survive.
- Step 3: Learn how sedimentary rock and strata are arrangedSedimentary rock is like a stack of layered cake: sediments settle layer upon layer, the lower ones first and the upper ones later, so the deeper the layer, the older it is. Geologists call these layers strata. Whichever layer holds a fossil records the age it lived in. Comparing fossils across strata is like leafing through a great book from ancient to recent, revealing the order in which life evolved.
- Step 4: Infer ancient environments from fossil kindsDifferent creatures live in different homes, so fossils act as witnesses of environments. Shells, ammonites and fish fossils in rock mean the place was once ocean; plenty of tree and dinosaur fossils mean it was forest or land; mammoth fossils in ice mean a cold climate then. Match the kinds of fossils with where such creatures live today, and the ancient scene can be inferred.
- Step 5: Infer surface changes from fossil positionsA fossil's position holds clues to change. Finding sea-creature fossils high on a mountain allows a sensible inference: the place was once seabed, later slowly pushed up by crustal movement into today's mountains. Again, marine sediments found deep inland hint at histories of seas advancing and retreating. Piecing together evidence from everywhere, scientists rebuild how land and sea have shifted over hundreds of millions of years.
- Step 6: Appreciate the value of fossilsFossils are key evidence for studying evolution, geological history and climate change, and they are a natural heritage that cannot be replaced. Follow museum rules; if you find something like a fossil in the countryside, do not hammer or dig it — photograph it and tell the authorities. Many scientists devote their lives to fossils, piecing together the Earth's history bit by bit. Respecting evidence and inferring carefully is a scientist's way — one we can all learn.
5Worked example Example
Example: Workers cutting a road along a Hong Kong hillside dig out sedimentary rock packed with shells and ammonite fossils. What does this tell us? Infer, step by step, what this place was like long ago, and give your reasons.
- First identify the evidence: shells and ammonites are sea creatures that live only in seawater.
- The fossils sit in sedimentary rock, showing the rock formed from sediments on the seabed.
- Make the inference: this hillside was once the seabed, where remains of sea life were buried in quantity.
- Explain the change: later, crustal movement slowly pushed the seabed layers up above the water into today's hills.
- Check the reasons: sea fossils plus sedimentary rock plus a hillside location — all three support the inference, so the conclusion is sound.
- Answer: Shells and ammonites are sea creatures, and their fossils lie in hillside sedimentary rock — proof that this place was once the seabed: sea creatures died, were buried by sediments, and became fossils in rock; later crustal movement pushed the seabed up into land, so the rock now stands on a hill. From the kind and position of the fossils we infer that the sea here became hills — the evidence is strong and the conclusion sound.
6Common mistakes Mistakes
7Quick check Quick check
Q1What is a fossil?
Q2In which kind of rock are fossils most often found?
Q3In sedimentary rock, what do deeper strata mean about age?
Q4Sea-creature fossils are found in mountain rock — what can we infer?
Q5Which ancient creature has been found whole in frozen ground?
8Recap Recap
- Fossils are ancient remains or traces in rock and ice.
- Most form in sedimentary rock; deeper strata are older.
- Fossil kinds reveal ancient environments.
- Sea fossils on mountains prove the crust lifted old seabeds.
- Fossils are irreplaceable — protect them and call the experts.