📚 6 Questions, Evidence, and Explanations: The Rock Cycle | 六个问题、证据与解释：岩石循环
Rocks are not permanent objects. They form, break down, and change over millions of years. In KS3 science you need to move beyond naming rocks and start using evidence to answer questions about how the rock cycle works. This article works through six key questions. For each question you will see the observable evidence and the scientific explanation that links the evidence to the rock cycle.
岩石并不是永久不变的物体。它们在数百万年间不断形成、分解和变化。在 KS3 科学课程中，你需要超越仅仅记住岩石名称，开始运用证据来回答关于岩石循环如何运作的问题。本文梳理六个关键问题。每个问题都会给出可观察的证据，以及将证据与岩石循环联系起来的科学解释。
Each question follows the same three-step pattern: describe what you can see, interpret what it means, and explain the process that produced it. If you can do all three steps, you are thinking like a geologist rather than a catalogue of rock names.
每个问题都遵循同样的三步模式：描述你看到的现象，解释它的含义，说明产生它的过程。如果你能完成这三步，你就是在像地质学家一样思考，而不是在背诵一堆岩石名称。
1. The Three Rock Families | 三大岩石家族
Before tackling the six questions, you need to recognise the three main rock families: igneous, sedimentary, and metamorphic. Igneous rocks form when molten rock cools and solidifies. Sedimentary rocks form when particles of older rocks, minerals, or shells are deposited, buried, and cemented. Metamorphic rocks form when existing rocks are changed by heat and pressure without melting.
在回答六个问题之前，你需要认识三大岩石家族：火成岩、沉积岩和变质岩。火成岩由熔融岩石冷却凝固形成。沉积岩由较老岩石的颗粒、矿物或贝壳沉积、埋藏并胶结而成。变质岩由原有岩石在未熔化的条件下受热和压力作用改变而成。
Igneous rocks are divided by where they cooled. Intrusive igneous rock, such as granite, cooled slowly underground, so its crystals are large enough to see. Extrusive igneous rock, such as basalt, cooled quickly at the surface, so its crystals are tiny or absent. Obsidian cooled so fast that it formed glass with no crystals at all.
火成岩按冷却位置分类。侵入火成岩（如花岗岩）在地下缓慢冷却，晶体大到肉眼可见。喷出火成岩（如玄武岩）在地表快速冷却，晶体极小甚至没有晶体。黑曜岩冷却极快，完全形成玻璃质，没有晶体。
Metamorphic rocks are divided by texture. Foliated metamorphic rocks, such as slate, schist, and gneiss, have minerals lined up in layers or bands. Non-foliated metamorphic rocks, such as marble and quartzite, are made of one or two minerals that do not align, so they look granular or sugary instead.
变质岩按结构分类。有叶理的变质岩（如板岩、片岩、片麻岩）矿物排列成层或条带。无叶理的变质岩（如大理岩、石英岩）由一两种不对齐排列的矿物组成，因此看起来呈颗粒状或糖粒状。
Each family has distinctive textures and minerals. These features are not random. They act as clues. When you describe a rock, you are gathering evidence. Later, you can use that evidence to explain how the rock formed and what happened to it afterwards.
每个家族都有独特的结构与矿物。这些特征并非随机产生，它们充当线索。当你描述一块岩石时，你正在收集证据。之后你可以用这些证据解释岩石如何形成，以及它后来经历了什么。
2. Question 1: How Do Crystals Record Cooling Rate? | 问题一：晶体如何记录冷却速率？
Evidence: look at the crystal size and how the crystals fit together. In granite the crystals interlock and are clearly visible, often several millimetres across. In basalt you need a hand lens to see them, and in obsidian you see a smooth glassy surface with a curved break called a conchoidal fracture.
证据：观察晶体大小以及晶体之间如何嵌合。花岗岩中晶体相互嵌生，肉眼清晰可见，常达数毫米。玄武岩需要用放大镜才能看到晶体，而黑曜岩表面光滑呈玻璃质，断裂面呈弯曲的贝壳状断口。
Explanation: crystals need time to grow. Molten rock contains ions moving randomly. When the melt cools slowly, ions have time to reach a growing crystal surface, so a few large crystals form. When the melt cools quickly, many small crystals start at once and none has time to grow large. Very rapid cooling freezes the disordered liquid structure into glass.
解释：晶体生长需要时间。熔融岩石中的离子随机运动。熔体缓慢冷却时，离子有时间到达晶体生长表面，于是形成少量大晶体。熔体快速冷却时，同时形成大量小晶核，但都没有时间长大。极快冷却则把无序的液态结构冻结成玻璃。
Further evidence comes from cooling cracks. When a thick lava flow cools and contracts, it splits into hexagonal columns, as seen at the Giant's Causeway. These columns show that cooling happened slowly and evenly over a large body of lava, which is consistent with the large-scale heat loss involved.
进一步的证据来自冷却裂隙。厚层熔岩流冷却收缩时，会裂成六边形柱状节理，如北爱尔兰巨人堤所见。这些石柱说明大体积熔岩缓慢而均匀地冷却，与大规模热量散失的过程一致。
Exam link: a question may show two photographs of igneous rock and ask which cooled more slowly. Answer in a chain: the visible interlocking crystals mean the magma cooled slowly underground, so the rock is intrusive and the ions had time to form large crystals.
考试链接：题目可能给出两张火成岩照片，问哪一块冷却更慢。要用因果链作答：可见的嵌生晶体说明岩浆在地下缓慢冷却，因此这块岩石是侵入岩，离子有时间形成大晶体。
3. Question 2: How Do Sedimentary Layers Record Past Environments? | 问题二：沉积岩层如何记录过去环境？
Evidence: sedimentary rocks show layers, called bedding planes, plus grain size, grain shape, sorting, colour, and sedimentary structures such as ripples, cross-bedding, and mud cracks. Fossils may also be present inside the layers.
证据：沉积岩显示层理面，以及颗粒大小、颗粒形状、分选性、颜色，还有波痕、交错层理、泥裂等沉积构造。层内还可能含有化石。
Explanation: each feature records the energy of the transport medium. Large angular fragments suggest fast-flowing water or ice close to the source, because heavy pieces cannot travel far and have little time to be smoothed. Well-rounded, well-sorted sand suggests long transport by water or wind, because collisions grind the grains and water or air sorts them by size.
解释：每个特征都记录搬运介质的能量。大块棱角状碎屑说明搬运距离短、水流或冰川流速快，因为重颗粒无法远运，也来不及被磨圆。圆度高、分选好的砂说明经水或风长距离搬运，因为颗粒互相碰撞被磨圆，水或空气又按大小把它们分选。
Individual structures give extra clues. Cross-bedding forms when sand is moved by currents and deposited on a sloping surface, so it indicates flowing water or wind. Symmetrical ripple marks form in shallow water moved by waves. Mud cracks form when wet mud dries out and shrinks, so they prove the sediment was exposed to air.
单个构造提供额外线索。交错层理形成于水流把砂搬运并沉积在倾斜面上，因此指示流动的水或风。对称波痕形成于波浪扰动的浅水。泥裂形成于湿泥干涸收缩，因此证明沉积物曾暴露在空气中。
Chemical and biological sedimentary rocks record chemistry and life. Limestone made of coral and shell fragments indicates warm, shallow, clear sea water. Rock salt and gypsum form when salty water evaporates, so they indicate a hot, dry environment. Iron-rich red beds indicate oxidising conditions, where iron minerals rusted.
化学与生物沉积岩记录化学条件与生命活动。由珊瑚与贝壳碎屑组成的石灰岩指示温暖、浅而清澈的海水。岩盐与石膏由咸水蒸发形成，因此指示炎热干燥的环境。富铁红色岩层指示氧化条件，铁矿物被氧化成铁锈色。
4. Question 3: How Does the Fossil Record Reveal Order and Change? | 问题三：化石记录如何揭示顺序与变化？
Evidence: fossils are found inside sedimentary layers, and different layers contain different fossils. The same fossil species may appear in layers thousands of kilometres apart. Fossils are rarely found in igneous rocks and are usually destroyed by metamorphism.
证据：化石发现于沉积岩层内部，不同层位含有不同化石。同一化石种可能出现在相隔数千千米的层位中。火成岩中极少发现化石，而变质作用通常会破坏化石。
Explanation: the principle of superposition states that in an undisturbed sequence of sedimentary layers, the lowest layer is the oldest and the highest is the youngest. Fossils therefore give a relative age: a species found in a low layer lived before a species found above it.
解释：叠覆原理指出，在未受扰动的沉积层序中，最下层最老，最上层最新。因此化石提供相对年龄：出现在下层的物种，生活在出现在上层物种之前。
Fossils also record past environments. Coral fossils indicate warm shallow seas; fern and coal-forming plant fossils indicate warm, wet land; ammonites indicate open marine water. If a rock contains marine fossils but is now found high in mountains, the evidence shows that the area was once under the sea and was later uplifted.
化石也记录过去的环境。珊瑚化石指示温暖浅海；蕨类与成煤植物化石指示温暖湿润的陆地；菊石化石指示开阔海域。如果一块岩石含有海生化石，如今却位于高山上，证据就说明该地区曾经位于海面之下，后来被抬升。
Cross-cutting relationships add order. If a magma intrusion or a fault cuts through layers, the feature doing the cutting must be younger than the layers it cuts. An unconformity, where a wavy erosion surface separates two sets of layers, records a gap in time when deposition stopped and erosion removed rock.
切割关系补充了顺序信息。如果岩浆侵入体或断层切穿岩层，那么起切割作用的地质体必定比被切割的岩层更年轻。不整合面（即波状侵蚀面分隔两套岩层）记录了一段沉积中断、侵蚀移走岩石的时间空白。
5. Question 4: How Do Metamorphic Rocks Record Heat and Pressure? | 问题四：变质岩如何记录热与压力？
Evidence: metamorphic rocks show recrystallised minerals that grew in the solid state, larger crystals than the original rock, aligned minerals forming foliation, and sometimes index minerals such as garnet, staurolite, kyanite, or sillimanite.
证据：变质岩显示在固态下重结晶生长的矿物、比原岩更大的晶体、排列成叶理的定向矿物，有时还出现石榴子石、十字石、蓝晶石、矽线石等指示矿物。
Explanation: heat and pressure make atoms rearrange within existing minerals or grow new minerals that are stable under the new conditions, but the rock does not melt. If it melted, it would become magma and later form igneous rock instead. Pressure that is greater in one direction lines up platy minerals such as mica at right angles to the stress.
解释：热和压力使原子在原有矿物内部重新排列，或生长出在新条件下稳定的新矿物，但岩石并不熔化。如果熔化，它就会变成岩浆，之后形成火成岩。方向性压力使云母等片状矿物垂直于应力方向排列。
A single rock type can record increasing metamorphic grade. Shale changes to slate at low grade, then to schist as mica grows and alignment strengthens, then to gneiss at high grade where light and dark minerals separate into bands. Limestone becomes marble, and sandstone becomes quartzite; both are non-foliated because they contain few platy minerals.
同一种原岩可以记录递增的变质程度。页岩在低级变质下变成板岩；云母长大、定向增强后变成片岩；高级变质下变成片麻岩，浅色与深色矿物分离成条带。石灰岩变成大理岩，砂岩变成石英岩；两者都无叶理，因为其中片状矿物很少。
Temperature and pressure ranges help explain the pattern. Metamorphism generally occurs between about 150 °C and 800 °C, at pressures from shallow crustal levels down to tens of kilometres depth. Contact metamorphism around an intrusion produces a narrow heated zone, while regional metamorphism affects huge areas during mountain building.
温度与压力范围有助于解释这一规律。变质作用通常发生在约 150 °C 至 800 °C 之间，压力从浅部地壳到数十千米深度不等。侵入体周围的接触变质形成狭窄的受热带，而区域变质在造山过程中影响广阔区域。
6. Question 5: How Do Weathering, Erosion and Deposition Move Material? | 问题五：风化、侵蚀与沉积如何搬运物质？
Evidence: broken rock fragments at the base of a cliff, rounded boulders in a river bed, fine mud in a lake, and thick layers of sand on a beach all show that rock material has been broken up and moved. Cracks widened by ice, plant roots prising apart rock, and iron-stained surfaces show breakdown in place.
证据：崖脚破碎的岩块、河床中磨圆的砾石、湖底的细泥、海滩上厚厚的砂层，都表明岩石物质被破碎并搬运。被冰撑宽的裂缝、植物根系撑裂的岩石、带铁锈色的表面则表明岩石在原地被分解。
Explanation: physical weathering breaks rock without changing its chemistry. Freeze-thaw action, salt crystallisation, root wedging, and heating and cooling all widen cracks. Chemical weathering changes the minerals. Carbonation dissolves limestone, oxidation rusts iron-rich minerals, and hydrolysis turns feldspar into clay minerals.
解释：物理风化在不改变化学组成的条件下破碎岩石。冻融作用、盐结晶、根劈作用、热胀冷缩都会撑宽裂缝。化学风化则改变矿物。碳酸盐化作用溶蚀石灰岩，氧化作用使富铁矿物生锈，水解作用把长石变成黏土矿物。
CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂
This equation shows why limestone caves form. Insoluble calcium carbonate reacts with dissolved carbon dioxide in rainwater to produce soluble calcium hydrogencarbonate, which is carried away in solution.
这个方程说明石灰岩洞穴为何形成。不溶的碳酸钙与雨水中的溶解二氧化碳反应，生成可溶的碳酸氢钙，被水溶液带走。
Erosion is the transport of the broken material, and deposition happens when the transporting medium loses energy. A fast river carries gravel and sand; when it slows on a floodplain it drops the gravel first, then sand, then silt, and finally clay. Wind deposits well-sorted, rounded sand in dunes, while ice drops unsorted, angular boulders and clay together as till.
侵蚀是破碎物质的搬运，沉积发生在搬运介质失去能量时。湍急河流搬运砾石和砂；当它在泛滥平原上减速，先沉积砾石，然后砂、粉砂，最后是黏土。风在沙丘中沉积分选好、磨圆的砂；冰川则把未分选、棱角状的砾石与黏土一起堆积成冰碛。
7. Question 6: Where Does the Energy Come From, and Is the Cycle Really a Cycle? | 问题六：能量来自哪里？循环真的是循环吗？
Evidence: volcanoes erupt, mountains rise, rivers carry sediment to the sea, and deep rocks are hot. Fossils of sea creatures are found in mountain ranges. These observations only make sense if material is moving between the surface and the interior of the Earth.
证据：火山喷发、山脉隆起、河流把沉积物带入海洋、深部岩石炽热。海洋生物的化石出现在山脉中。这些观察只有在物质在地球表层与内部之间移动时才能得到解释。
Explanation: two main energy sources drive the rock cycle. Heat inside the Earth, from radioactive decay and leftover heat from formation, drives melting, metamorphism, plate movement, and mountain building. Energy from the Sun drives the water cycle, weathering, erosion, and transport. Gravity drives material downhill and pulls dense plates downwards.
解释：驱动岩石循环的主要有两个能量来源。地球内部的热量来自放射性衰变和形成时的残余热，驱动熔融、变质、板块运动与造山。太阳的能量驱动水循环、风化、侵蚀与搬运。重力使物质向低处移动，并把致密的板块向下拉。
The rock cycle is not a single fixed loop. Any rock can be weathered, buried, metamorphosed, melted, or uplifted, and the order of steps can vary. A sedimentary rock can be buried and metamorphosed without ever melting. An igneous rock can be eroded directly into sediment.
岩石循环不是一条固定的单向环路。任何岩石都可以被风化、埋藏、变质、熔融或抬升，步骤顺序可以不同。沉积岩可以被埋藏并变质而从不熔化。火成岩也可以直接被侵蚀变成沉积物。
Timescales matter too. A volcano can build a new rock in days, but deep burial and metamorphism may take millions of years. The rock cycle is also linked to the carbon cycle: shell and coral material forms limestone, and later heating or metamorphism can release carbon dioxide back to the atmosphere.
时间尺度也很重要。火山可以在数天内形成新岩石，而深埋与变质可能耗时数百万年。岩石循环还与碳循环相连：贝壳与珊瑚物质形成石灰岩，之后的加热或变质可把二氧化碳释放回大气。
8. Key Processes and Equations to Recognise | 需要认识的关键过程与方程
Cooling and crystallisation: molten rock loses heat and crystals grow. The slower the cooling, the larger the crystals, which is why granite has visible grains and basalt does not.
冷却与结晶：熔融岩石失去热量并长出晶体。冷却越慢，晶体越大，所以花岗岩颗粒肉眼可见，玄武岩则不然。
Compaction and cementation: loose sediment is squeezed by the weight of overlying layers, and minerals such as quartz, calcite, or iron oxide precipitate between grains to bind them into solid rock.
压实与胶结：松散沉积物被上覆岩层压紧，石英、方解石或氧化铁等矿物在颗粒间沉淀，把它们胶结成坚硬的岩石。
CaCO₃ → CaO + CO₂
This reaction occurs when limestone is heated very strongly, for example in a kiln or during high-temperature metamorphism with silica present, producing calcium oxide and carbon dioxide.
这一反应发生在石灰岩被强烈加热时，例如在石灰窑中，或存在二氧化硅时的高温变质过程中，生成氧化钙和二氧化碳。
Metamorphic recrystallisation: in the solid state, minerals such as calcite in limestone grow larger and interlock to form marble, while quartz grains in sandstone fuse into the tight mosaic of quartzite.
变质重结晶：在固态下，石灰岩中的方解石等矿物长大并相互嵌生形成大理岩，砂岩中的石英颗粒则紧密镶嵌成石英岩。
Weathering reactions: carbonation dissolves limestone as shown earlier, oxidation turns iron silicates into iron oxides, and hydrolysis converts feldspar into clay minerals plus dissolved ions.
风化反应：如前所示，碳酸盐化作用溶蚀石灰岩；氧化作用把铁硅酸盐变成氧化铁；水解作用把长石转化为黏土矿物和溶解离子。
9. Evidence Table: Matching Features to Processes | 证据表：把特征与过程配对
| Feature | 特征 | Evidence | 证据 | Process | 推断过程 |
| Large interlocking crystals | 大块嵌生晶体 | Visible grains in granite | 花岗岩中肉眼可见颗粒 | Slow cooling underground (intrusive) | 地下缓慢冷却（侵入） |
| Glassy texture | 玻璃质结构 | Obsidian with conchoidal fracture | 黑曜岩呈贝壳状断口 | Extremely rapid cooling at the surface | 地表极快冷却 |
| Rounded, well-sorted sand | 磨圆、分选好的砂 | Sandstone grains under a lens | 放大镜下砂岩颗粒 | Long transport by water or wind | 经水或风长距离搬运 |
| Ripple marks | 波痕 | Wavy patterns on a bedding plane | 层理面上的波状纹 | Shallow water moved by waves | 波浪扰动的浅水环境 |
| Fossils of coral | 珊瑚化石 | Shell fragments in limestone | 石灰岩中的贝壳碎屑 | Warm, shallow, clear sea | 温暖、浅而清澈的海 |
| Foliation | 叶理 | Aligned mica in schist | 片岩中定向排列的云母 | Directed pressure during metamorphism | 变质过程中的方向性压力 |
| Mud cracks | 泥裂 | Polygon patterns in mudstone | 泥岩中的多边形裂纹 | Wet mud dried and sh
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