📚 10 Fossils: Key Chemistry Ideas | 10 个化石知识：化学要点
Fossils are not just dusty museum displays. In chemistry, fossils and the fuels made from them explain how carbon moves between living things, rocks, oceans and the atmosphere. This KS3 chemistry article explores ten important ideas, from how fossils form to why burning fossil fuels affects our planet.
化石不只是博物馆里布满灰尘的展品。在化学中，化石以及由化石形成的燃料帮助我们理解碳如何在生物、岩石、海洋和大气之间循环。这篇 KS3 化学文章探讨十个重要知识点，从化石如何形成到为什么燃烧化石燃料会影响地球。
1. What Are Fossils? | 什么是化石？
Fossils are the preserved remains, impressions, or traces of organisms that lived in the geological past. They are usually found in sedimentary rocks such as limestone, shale, and sandstone.
化石是保存在地质历史时期生物遗骸、印痕或活动痕迹。它们通常出现在沉积岩中，如石灰岩、页岩和砂岩。
From a chemistry point of view, a fossil often forms when the original organic material is replaced by minerals such as calcium carbonate, silica, or pyrite. Over time, the chemical composition changes from living tissue to rock-like minerals.
从化学角度看，化石通常是原始有机物质被碳酸钙、二氧化硅或黄铁矿等矿物替代后形成的。随着时间推移，化学成分由生物组织变为类似岩石的矿物。
2. How Fossils Form | 化石如何形成
Fossilisation usually starts with rapid burial. When an organism is covered by mud, sand, or volcanic ash, it is protected from scavengers and decay.
化石形成通常始于快速掩埋。当生物被泥土、沙子或火山灰覆盖时，它就能避免被食腐动物吃掉或快速腐烂。
As more sediment piles up, pressure increases and groundwater moves through the pores. Dissolved minerals slowly replace the original hard parts, or fill the empty spaces left when soft parts decay. Common minerals involved are silica (SiO₂) and calcium carbonate (CaCO₃).
随着沉积物越堆越厚，压力增大，地下水在孔隙中流动。溶解的矿物慢慢替换原始坚硬部分，或填充软组织腐烂后留下的空隙。常见的参与矿物是二氧化硅（SiO₂）和碳酸钙（CaCO₃）。
3. Types of Fossils | 化石的类型
Scientists divide fossils into two main groups: body fossils and trace fossils. Body fossils preserve parts of an organism, while trace fossils record its activity.
科学家将化石分为两大类：实体化石和遗迹化石。实体化石保存生物体的一部分，而遗迹化石记录生物的活动。
- Body fossils: bones, shells, teeth, leaves. | 实体化石：骨骼、贝壳、牙齿、树叶。
- Trace fossils: footprints, burrows, coprolites. | 遗迹化石：足迹、洞穴、粪便化石。
- Molds and casts: impressions left in rock or filled by minerals. | 印模和铸型：岩石中留下的印痕或被矿物充填的模型。
In chemistry, the type of mineral replacement affects what the fossil is made from. Calcified fossils are rich in CaCO₃, silicified fossils in SiO₂, and pyritised fossils in FeS₂.
在化学上，矿物替换的类型决定了化石的成分。钙化化石富含 CaCO₃，硅化化石富含 SiO₂，黄铁矿化化石富含 FeS₂。
4. From Fossils to Fossil Fuels | 从化石到化石燃料
Fossil fuels are not fossils in the usual sense, but they are the remains of ancient living things. Over millions of years, heat and pressure convert buried plants and marine plankton into coal, oil, and natural gas.
化石燃料并不是通常意义上的化石，但它们是远古生物的遗骸。经过数百万年，热量和压力将埋藏在地下的植物和海洋浮游生物转化为煤、石油和天然气。
The key chemical idea is energy storage. Ancient organisms captured solar energy through photosynthesis. When they died and were buried, some of that chemical energy remained trapped in carbon-rich compounds.
关键的化学概念是能量储存。古代生物通过光合作用捕获太阳能。当它们死亡并被掩埋后，一部分化学能仍储存在富含碳的化合物中。
5. Coal Formation Chemistry | 煤形成的化学
Coal forms mainly from plant material in ancient swampy forests. First, dead plants form peat. As peat is buried deeper, temperature and pressure rise, driving off water and gases and increasing the proportion of carbon.
煤主要由古代沼泽森林中的植物物质形成。首先，死去的植物形成泥炭。随着泥炭被埋得更深，温度和压力升高，水分和气体被排出，碳的比例增加。
| Stage | 阶段 | Carbon content | 碳含量 |
|---|---|
| Peat | 泥炭 | about 50–60% | 约 50–60% |
| Lignite | 褐煤 | about 60–70% | 约 60–70% |
| Bituminous coal | 烟煤 | about 70–85% | 约 70–85% |
| Anthracite | 无烟煤 | above 85% | 85% 以上 |
This process is called carbonisation. It is a chemical change because large plant molecules break down into smaller, carbon-rich structures and volatile compounds escape.
这个过程称为碳化作用。它是一种化学变化，因为大型植物分子分解为更小、富含碳的结构，挥发性化合物逸出。
6. Oil and Natural Gas Formation | 石油和天然气的形成
Oil and natural gas come mainly from tiny marine organisms such as plankton and algae. When these organisms died, they sank to the sea floor and were buried under sediment.
石油和天然气主要来自微小的海洋生物，如浮游生物和藻类。这些生物死亡后沉入海底，被沉积物掩埋。
Under high temperature and pressure, the organic material changes into liquid oil and gaseous hydrocarbons. Natural gas is mostly methane (CH₄), the smallest hydrocarbon molecule.
在高温高压下，有机物质转变为液态石油和气态碳氢化合物。天然气的主要成分是甲烷（CH₄），即最小的碳氢化合物分子。
Hydrocarbons are compounds containing only hydrogen and carbon. Crude oil is a mixture of many different hydrocarbons that can be separated by fractional distillation.
碳氢化合物是只含氢和碳的化合物。原油是多种不同碳氢化合物的混合物，可以通过分馏进行分离。
7. Chemical Composition of Fossil Fuels | 化石燃料的化学成分
All fossil fuels are carbon-based, but their states and compositions differ. Coal is mainly solid carbon with some hydrogen, sulfur, nitrogen, and mineral ash. Oil is a liquid mixture of medium-sized hydrocarbons. Natural gas is mostly gaseous methane, CH₄.
所有化石燃料都以碳为基础，但状态和成分各不相同。煤主要是固体碳，并含少量氢、硫、氮和矿物质灰分。石油是中等大小碳氢化合物的液体混合物。天然气主要是气态甲烷 CH₄。
Because fossil fuels contain sulfur and nitrogen impurities, burning them can release sulfur oxides (SO₂, SO₃) and nitrogen oxides (NO, NO₂). These gases affect air quality and cause acid rain.
由于化石燃料含有硫和氮杂质，燃烧时会释放硫氧化物（SO₂、SO₃）和氮氧化物（NO、NO₂）。这些气体会影响空气质量并造成酸雨。
8. Combustion of Fossil Fuels | 化石燃料的燃烧
Combustion is a chemical reaction with oxygen. When fossil fuels burn completely, the products are carbon dioxide and water. This is called complete combustion.
燃烧是与氧气发生的化学反应。当化石燃料完全燃烧时，产物是二氧化碳和水。这称为完全燃烧。
methane + oxygen → carbon dioxide + water
CH₄ + 2O₂ → CO₂ + 2H₂O
In limited oxygen, incomplete combustion occurs. It produces carbon monoxide (CO), a toxic gas, and soot, which is mostly unburned carbon particles.
在氧气不足时，会发生不完全燃烧。它产生有毒气体一氧化碳（CO）以及烟灰，烟灰主要是未燃烧的碳颗粒。
Carbon monoxide is dangerous because it binds to haemoglobin in red blood cells more strongly than oxygen does, reducing the blood's ability to carry oxygen.
一氧化碳很危险，因为它与红细胞中的血红蛋白结合比氧气更强，从而降低血液输送氧气的能力。
9. Environmental Impact: Carbon Cycle and Climate | 环境影响：碳循环与气候
Fossil fuels are part of the long-term carbon cycle. For millions of years, carbon was locked up underground. Burning fossil fuels releases that carbon quickly as carbon dioxide, CO
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