Grade 7 · English for Korean learners
A dinosaur could weigh several tonnes, frighten everything nearby, and still disappear almost completely after death. Meanwhile, a small shell might survive for hundreds of millions of years. Nature has peculiar filing rules. Fossils are the remains or traces of past life preserved through geological time. They help scientists reconstruct vanished animals, changing climates, and the history of evolution. The difficult part is that most organisms never enter the archive. What survives is precious evidence, but it is also an incomplete sample.
In the News
Fossils found in 1970s are most recent ancestor of tyrannosaurs, scientists say — The Guardian, 11 June 2025. Researchers reassessed old Mongolian specimens. Their classification changed.
The 280m-year-old fossil reptile that turned out to be a forgery — The Guardian, 28 February 2024. Imaging exposed painted material. Apparent detail required testing.
Fangs and toilet seat-shaped head: giant salamander-like fossil found in Namibia — The Guardian, 3 July 2024. A discovery widened knowledge of ancient predators. Location mattered.
What do you think?
1] Why does a footprint last longer in mud than on water?
2] What could your bedroom reveal about you after you leave?
3] Why do dry leaves break easily?
4] Which parts of a fish disappear first?
5] How could a mark show that something moved?
6] Why might two beaches preserve different objects?
7] What makes an object convincing evidence?
8] How could you tell a copy from an original?
9] Why is a missing page troublesome?
10] Can a broken object still provide useful information?
11] Why does knowing where an object came from matter?
12] What might shells on a mountain suggest?
13] How could a tooth reveal a diet?
14] Why should several people check an unusual discovery?
15] What could an old tree stump reveal?
16] Why do some materials last longer than others?
17] How might a river sort objects by size?
18] When is a good guess still uncertain?
19] Why might a collector hide a discovery?
20] How would you preserve a muddy footprint?
Did You Know?
1] Trilobites lived for roughly 270 million years before becoming extinct about 252 million years ago.
2] Coprolites are fossilised dung; they can contain evidence of ancient meals.
3] Birds are living dinosaurs, descended from theropod dinosaurs.
4] A cast of a shell can preserve its shape even after the original shell dissolves.
Vocabulary
- remains — 남은 흔적이나 유해
- trace — 흔적
- preserve — 보존하다
- bury — 묻다
- decay — 썩다
- shell — 껍데기
- pore — 작은 구멍
- dissolve — 녹아 없어지다
- impression — 눌려 남은 자국
- footprint — 발자국
- burrow — 굴
- layer — 층
- ash — 재
- clock — 시계
- estimate — 추정하다
- confidence — 확신
- tooth — 이빨
- diet — 먹이 구성
- joint — 관절
- feather — 깃털
- climate — 기후
- sample — 표본
- bias — 편향
- excavate — 발굴하다
- label — 표지를 붙이다
- fragile — 부서지기 쉬운
- forgery — 위조품
- collection — 수집 자료
- extinct — 멸종한
- heritage — 유산
Glossary
Fossil — A preserved remain or trace comes from past life. It is evidence of an organism. It need not be a bone. 화석.
Sediment — Loose particles settle on land or underwater. They include sand and mud. They can bury living remains. 퇴적물.
Permineralisation — Minerals enter pores in buried material. They form solid deposits there. Original structure may remain. 광물 충전 작용.
Mould — A buried object can leave an empty shape. The object itself may dissolve. The hollow records its outside. 주형.
Cast — Material can fill a mould. It then hardens. The result copies an earlier shape. 충전 화석.
Stratigraphy — Scientists study rock layers and their relationships. Layers help establish event order. Disturbance must be considered. 층서학.
Radiometric dating — Some atoms change at known rates. Scientists measure suitable materials. These measurements help estimate age. 방사성 동위원소 연대 측정.
Evolution — Inherited characteristics change across generations. Populations change rather than individual lifetimes. Fossils provide historical evidence. 진화.
Palaeontology — This science studies ancient life. It uses fossils and geological information. Researchers test explanations against evidence. 고생물학.
Taphonomy — Scientists study what happens after death. Burial and decay affect preservation. These processes influence the record. 화석화 과정 연구.
How Life Becomes Evidence
A fossil is a preserved remain or trace of an organism from the geological past. A bone, shell, leaf impression, footprint, or burrow can qualify. Most dead organisms decay or are eaten before preservation begins. Bacteria break down soft tissues, and weather damages exposed remains. Rapid burial in sediment can slow these processes. Hard parts usually survive better than skin or internal organs. This explains why museums have many teeth and rather fewer ancient stomachs. Preservation is not a reward for being impressive. It depends on the material, surrounding conditions, and events after death.
1] Why does rapid burial improve preservation?
2] Why are hard parts common in collections?
Groundwater can carry dissolved minerals into the tiny spaces, or pores, inside buried wood and bone. Minerals then form deposits in those spaces. This process, called permineralisation, can preserve detailed internal structure. Other processes replace original material with different minerals. These changes often happen gradually, while sediment above becomes rock. A mineral-filled bone therefore need not contain only the original animal material. Scientists examine its structure and chemistry to understand what survived. Calling every fossil a stone animal is misleading. The object may be partly original, partly altered, or mainly a record of shape.
1] How do minerals enter buried material?
2] Why can a preserved bone contain different materials?
A shell can dissolve after sediment around it becomes firm. Its empty impression is a mould. If new sediment or minerals fill that space and harden, the result is a cast. Imagine removing a biscuit from soft clay, then filling the hollow with another material. The copy records the outside shape, but not necessarily the biscuit’s ingredients. Fossil casts have the same limitation. Flattened leaves can instead leave thin carbon-rich films. Amber sometimes traps small organisms in tree resin. These pathways preserve different information, so scientists must identify the preservation process before interpreting the object.
1] How does a cast differ from a mould?
2] What information might a cast fail to preserve?
Trace fossils record behaviour rather than the organism’s body. Footprints can show walking direction, approximate stride, and whether several animals crossed the same surface. Burrows reveal activity below ground. Coprolites, or fossilised dung, sometimes contain bone fragments, scales, or plant material from meals. This is useful dietary evidence, although working with it offers few opportunities for elegance. A trace does not always identify its maker exactly. Several species may produce similar marks. Researchers compare shape, size, rock setting, and nearby remains. They distinguish direct observations from interpretations, especially when proposing social behaviour from a trackway.
1] What can a trackway reveal?
2] Why is identifying a trace’s maker difficult?
Finding Ages and Reconstructing Bodies
Rock layers often preserve a sequence of events. In an undisturbed stack of sedimentary layers, lower layers formed before higher ones. This principle helps establish relative age: which object is older, without assigning a calendar date. However, folding, faulting, and erosion can disturb the sequence. A river can also move an older fossil into younger sediment. Researchers therefore study the surrounding geology rather than merely reading the stack like a tidy sandwich. Stratigraphy combines layer relationships, rock types, and changes across an area. The location of a specimen can be as informative as the specimen itself.
1] What does relative age tell scientists?
2] How could an older specimen enter a younger layer?
Radiometric dating uses atoms that change into other atoms at predictable rates. Suitable volcanic minerals can record when they cooled. An ash layer above or below a fossil-bearing bed may therefore help limit the bed’s age. Scientists do not normally date a dinosaur bone by measuring its carbon-14. Carbon-14 is useful for comparatively recent organic material, generally up to around 50,000 years under favourable conditions. Dinosaurs outside the bird lineage disappeared about 66 million years ago. That is far beyond this method’s useful range. Different materials and timescales require different radioactive clocks and careful laboratory checks.
1] Why is carbon-14 unsuitable for dinosaur ages?
2] How can volcanic ash help date a nearby layer?
An isolated tooth can reveal surprisingly much. Sharp cutting surfaces may suggest slicing flesh, while broad grinding surfaces may indicate processing tough plant food. Wear marks provide additional evidence of use. Nevertheless, shape alone cannot describe every meal. Some animals eat varied diets, and damaged teeth can mislead. Scientists compare fossils with living animals and examine several kinds of evidence together. Chemical signals sometimes add information about diet or environment. A tooth is a clue, not a complete restaurant receipt. The strongest reconstruction explains all available observations while recognising which details cannot yet be recovered with confidence.
1] How can tooth shape suggest diet?
2] Why should scientists use more than tooth shape?
Reconstructing a skeleton requires matching joints, comparing related animals, and checking whether proposed positions are physically possible. Missing bones are sometimes represented by casts or models in museum displays. These additions should be identified rather than quietly treated as discoveries. Soft features are harder to reconstruct. Exceptional fossils can preserve feather impressions or skin outlines, but they do not reveal every colour or sound. Artists work from evidence and make choices where evidence ends. A mounted animal can look wonderfully certain while containing several reasonable guesses. Scientists revise reconstructions when better specimens or improved methods become available.
1] Why might a display contain model bones?
2] Which features are difficult to reconstruct?
Reading Evolution and Ancient Environments
Fossils show that organisms have changed over deep time. Different combinations of features appear in different geological periods. Some fossils preserve characteristics expected between earlier and later groups, providing evidence of evolutionary relationships. They are not necessarily the direct ancestors of every later species. Evolution produces branching family histories, and most branches eventually become extinct. A living species is not a creature waiting to become a supposedly higher species. Researchers compare many inherited features to test relationships. Fossils contribute historical information that living organisms alone cannot provide, especially about groups whose members vanished long before anyone could study them.
1] Why is evolution represented by branching relationships?
2] Why need an intermediate fossil not be a direct ancestor?
Fossils also reveal former environments. Reef-building organisms in a rock can suggest an ancient sea, while certain plant remains provide clues about land conditions. Shells high in mountains do not mean that shellfish learned mountaineering. Rocks formed underwater can later be lifted as tectonic plates move. Scientists combine biological evidence with sediment structures and regional geology. A single shell might have been transported, so a whole assemblage is more reliable than one striking object. Reconstructing climate requires further care because organisms tolerate ranges of conditions. Evidence usually supports a bounded interpretation rather than a perfectly detailed ancient weather forecast.
1] How can marine remains reach a mountain?
2] Why is an assemblage more useful than one shell?
The fossil record is an uneven sample of past life. Animals with hard shells are often easier to preserve than soft-bodied animals. Lakes and seas commonly accumulate sediment, while exposed uplands may lose it through erosion. Researchers also find more specimens in places that are accessible and well studied. These differences create preservation and sampling bias. A missing fossil therefore does not prove that an organism never existed. However, incompleteness does not make all explanations equally good. Patterns repeated across many sites remain powerful evidence. Scientists ask how missing information could affect a conclusion, then seek independent ways to test it.
1] What creates preservation bias?
2] Why does a missing fossil not prove absence?
Mass extinctions appear as major losses of species across relatively short geological intervals. The event about 66 million years ago removed non-bird dinosaurs and many other groups. Evidence includes the large Chicxulub impact crater, unusual chemical signals, and changes in fossil assemblages. Not every animal died, and surviving groups later diversified. Scientists investigate how darkness, disrupted food webs, and other environmental changes affected organisms differently. This is useful for understanding ecosystem vulnerability, although ancient events are not exact copies of present problems. The record shows that recovery can involve enormous timescales. Losing biodiversity is easier than replacing it.
1] What evidence supports the end-Cretaceous impact?
2] Why should ancient and present crises not be treated as identical?
Protecting Discoveries and Improving Research
Finding a promising fossil is only the beginning of an excavation. Researchers record its position, surrounding layers, orientation, and associated material before removal. They may protect fragile bones with a supporting jacket for transport. In a laboratory, preparation removes surrounding rock carefully, often with small tools. Poor handling can destroy information that no photograph can restore. Each specimen needs a label linking it to field notes. Without that connection, an interesting bone becomes much less useful scientifically. Collecting rules differ between places, and permission matters. A dramatic discovery does not automatically give its finder ownership of the site or specimen.
1] Why must position be recorded before removal?
2] Why does a label matter scientifically?
Computed tomography, or CT scanning, combines X-ray measurements to reveal internal structure. It can show hidden bones or cavities without cutting a specimen apart. Digital models allow researchers in different countries to compare shapes and test reconstructions. However, scanning does not automatically reveal every detail. Image quality depends on resolution and differences between materials. Dense minerals may hide delicate structures, and computer processing can introduce errors. Researchers check digital interpretations against the physical specimen. The computer is an instrument, not an oracle with a convenient power cable. New methods are strongest when they answer clear questions and their limitations are understood.
1] How can CT scanning protect a specimen?
2] Why must digital interpretations be checked?
Forgery can imitate evidence, while accidental alteration can also mislead. Paint may resemble soft tissue, and assembled bones from different animals may produce a convincing-looking skeleton. Researchers investigate suspicious material using microscopy, imaging, chemistry, and its collection history. A claim should survive examination beyond its attractive appearance. Museum collections are valuable because specimens remain available for repeated study. Commercial collecting can rescue material, but it can also separate objects from their context or restrict access. These are practical trade-offs rather than reasons to distrust every collector. Scientific value depends heavily on trustworthy records, lawful handling, and opportunities for independent examination.
1] How can researchers investigate a suspected forgery?
2] How might private ownership affect research?
Future discoveries will include both newly excavated specimens and old objects examined in new ways. A museum drawer may contain material collected decades ago that answers a question nobody then thought to ask. Better imaging and chemical analysis can extract evidence while limiting damage. Meanwhile, erosion, building work, and unlawful collecting can destroy sites before study. Protecting geological heritage preserves opportunities for later researchers. Citizens can help by reporting finds responsibly and recording locations rather than removing everything immediately. The aim is not simply to acquire impressive objects. It is to preserve reliable evidence about life, environments, and change through time.
1] Why can old collections produce new discoveries?
2] How can a citizen protect a find’s scientific value?
Homework
Writing tasks
1] Write approximately one page. Explain why a footprint sometimes survives while a whole body disappears.
2] Write approximately one page. Argue which parts of a modern beach would be most likely to leave lasting evidence.
3] Write approximately one page. Explain what a broken tooth could and could not reveal about an animal.
4] Write approximately one page. Describe how you would distinguish an original object from a cast.
5] Write approximately one page. Explain why knowing a discovery’s location changes its value.
6] Write approximately one page. Argue whether a museum should label every reconstructed bone.
7] Write approximately one page. Explain how missing evidence can affect an interpretation without making it useless.
8] Write approximately one page. Discuss whether private collectors should make important specimens available for research.
9] Write approximately one page. Explain why a shell on a mountain requires geological reasoning.
10] Write approximately one page. Propose a responsible response to finding an unusual object during a walk.
Debate topics
1] Should important specimens remain in public collections?
Side A — Yes, because: 1) access supports checking; 2) records can be maintained; 3) future methods may help.
Side B — No, because: 1) private collectors sometimes rescue material; 2) public storage is limited; 3) loans can provide access.
2] Should museums display reconstructions with many missing parts?
Side A — Yes, because: 1) displays explain scale; 2) models connect fragments; 3) clear labels can show uncertainty.
Side B — No, because: 1) visitors may overlook labels; 2) guesses may become memorable errors; 3) fragments can teach evidence directly.
3] Should a fragile specimen be scanned before physical preparation?
Side A — Yes, because: 1) scanning may reveal hidden structure; 2) it records initial condition; 3) it can guide preparation.
Side B — No, because: 1) scanning costs money; 2) some materials scan poorly; 3) urgent conservation may take priority.
Test questions
Answer the following questions in full sentences. If you don’t know the right answer, add a (?) mark, and later we can look at it together.
1] What is a fossil?
2] Why does rapid burial help?
3] What happens during permineralisation?
4] How does a mould form?
5] How does a cast form?
6] What is a trace fossil?
7] What can a coprolite reveal?
8] What does relative dating establish?
9] How can geological disturbance confuse layer order?
10] Why is carbon-14 unsuitable for non-bird dinosaur remains?
11] How can an ash layer help establish age?
12] What evidence can indicate diet?
13] Why should reconstructed bones be labelled?
14] How do fossils support evolution?
15] How can marine fossils occur in mountains?
16] What is preservation bias?
17] Name evidence linked to the extinction event about 66 million years ago.
18] Why are field notes essential?
19] What can CT scanning reveal?
20] Why can museum collections support future discoveries?
Teaching illustrations and similes
1] Rapid burial — Covering a fragile document protects it from disturbance; burial does not guarantee preservation.
2] Permineralisation — Mineral deposits fill a sponge’s holes; bone has a more complex structure.
3] Mould — An empty jelly mould records shape; it does not preserve ingredients.
4] Cast — Hardened material copies a hollow; it may lack internal anatomy.
5] Layer order — Stacked letters suggest a sequence; geological disturbance can rearrange the stack.
6] Dating clocks — Different clocks cover different ranges; radioactive decay is a physical process, not a mechanical clock.
7] Reconstruction — A broken puzzle needs matching pieces; invented pieces must be identified.
8] Evolution — A branching family tree shows relationships; fossil species need not be direct ancestors.
9] Sampling bias — A lost-property box overrepresents durable objects; the fossil record involves additional geological filters.
10] Collection records — An address connects a parcel to its origin; fossil context includes layers and associated evidence.
