📚 Human Fossils: Chemical Clues from the Past | 人类化石：来自过去的化学线索
Fossils are often seen as remains of ancient life, but from a chemical point of view they are also a record of how minerals replace organic matter over thousands or millions of years. This article explores the chemistry behind human fossils, including bone composition, mineral replacement, radioactive dating and trace-element analysis.
化石通常被视为古代生命的遗骸，但从化学角度看，它们也是矿物在数千年或数百万年间取代有机物质的记录。本文探讨人类化石背后的化学，包括骨骼成分、矿物置换、放射性定年和微量元素分析。
1. What Are Human Fossils? | 什么是人类化石？
A fossil is any preserved evidence of past life. Human fossils may include bones, teeth, footprints or even fossilised faeces. In chemistry, we focus on the materials that make up these fossils and how their original biological molecules change over time.
化石是过去生命保存下来的任何证据。人类化石可能包括骨骼、牙齿、脚印甚至粪便化石。在化学中，我们关注构成这些化石的材料，以及它们原有的生物分子如何随时间发生变化。
Most human fossils are not original bone; they are mineral copies. The original calcium phosphate may remain partly, but much organic collagen protein decays and is replaced by minerals from groundwater.
大多数人类化石并不是原始骨骼，而是矿物复制品。原有的磷酸钙可能部分保留，但许多有机胶原蛋白会分解，并被地下水中的矿物取代。
2. The Chemical Composition of Bones and Teeth | 骨骼和牙齿的化学成分
Living human bone is a composite material. It contains about 70% inorganic mineral and 30% organic matter by dry mass. The main inorganic mineral is a calcium phosphate called hydroxyapatite.
活体人类骨骼是一种复合材料。按干重计算，它含有约 70% 的无机矿物和 30% 的有机物质。主要的无机矿物是一种叫做羟基磷灰石的磷酸钙。
Ca₁₀(PO₄)₆(OH)₂
Hydroxyapatite gives bone its hardness and strength. The organic part is mostly collagen, a protein that provides flexibility. This combination makes bone tougher than mineral alone.
羟基磷灰石赋予骨骼硬度和强度。有机部分主要是胶原蛋白，一种提供柔韧性的蛋白质。这种组合使骨骼比单独的矿物更坚韧。
3. How Fossils Form: Mineral Replacement | 化石如何形成：矿物置换
Fossilisation often begins when an organism is buried quickly in sediment. Oxygen is limited, so decay is slowed. Groundwater then moves through the buried remains, carrying dissolved ions such as carbonate, silicate and phosphate.
化石形成通常始于生物体被沉积物迅速掩埋。氧气有限，因此腐烂减慢。随后地下水穿过埋藏的遗骸，携带溶解的离子，如碳酸根、硅酸根和磷酸根。
These ions can precipitate inside tiny pores in the bone. Step by step, the original organic material is replaced by minerals such as calcite or silica. This process is called permineralisation or replacement.
这些离子可以在骨骼的微小孔隙中沉淀。原始有机物质逐步被方解石或二氧化硅等矿物取代。这一过程称为过矿化或置换作用。
Sometimes whole molecules are replaced while the shape remains unchanged. This is why a fossil can look exactly like the original bone even though its chemistry is now completely different.
有时整个分子被取代，而形状保持不变。这就是为什么化石看起来与原始骨骼完全一样，尽管其化学成分现在已经完全不同。
4. Common Fossil Minerals: Silica, Calcite and Phosphate | 常见化石矿物：二氧化硅、方解石和磷酸盐
Different environments produce different fossil minerals. Silica (SiO₂) is common in volcanic ash beds, where it forms very detailed fossils. Calcite (CaCO₃) is common in limestone caves and marine sediments.
不同的环境产生不同的化石矿物。二氧化硅（SiO₂）常见于火山灰层中，能形成非常精细的化石。方解石（CaCO₃）常见于石灰岩洞穴和海洋沉积物中。
Phosphate fossils retain more of the original bone mineral. Apatite group minerals, including hydroxyapatite and fluorapatite, are often found in human fossils. Fluorapatite forms when fluoride ions replace hydroxide ions in hydroxyapatite.
磷酸盐化石保留了更多原始骨骼矿物。磷灰石族矿物，包括羟基磷灰石和氟磷灰石，常见于人类化石中。当氟离子取代羟基磷灰石中的氢氧根离子时，就会形成氟磷灰石。
Ca₁₀(PO₄)₆(OH)₂ + 2F⁻ → Ca₁₀(PO₄)₆F₂ + 2OH⁻
This reaction shows how chemical substitution can change the mineral while preserving the bone shape. The overall structure remains similar, so the fossil still looks like bone.
该反应表明化学取代如何在保留骨骼形状的同时改变矿物。整体结构保持相似，因此化石看起来仍然像骨骼。
5. Carbon-14 Dating: A Radioactive Clock | 碳-14 定年：放射性时钟
One of the most important chemical tools for dating human fossils is carbon-14 dating. Carbon has three main isotopes: carbon-12, carbon-13 and carbon-14. Only carbon-14 is radioactive.
测定人类化石年代最重要的化学工具之一是碳-14 定年。碳有三种主要同位素：碳-12、碳-13 和碳-14。只有碳-14 具有放射性。
Living organisms constantly take in carbon from food and the atmosphere. While alive, the ratio of carbon-14 to carbon-12 stays roughly constant. When the organism dies, it stops taking in carbon-14.
活体生物不断从食物和大气中摄取碳。活着时，碳-14 与碳-12 的比例大致保持恒定。生物死亡后，便不再摄入碳-14。
The existing carbon-14 then decays to nitrogen-14 by beta emission. By measuring the remaining carbon-14, scientists can estimate the time since death.
现有的碳-14 随后通过 β 衰变为氮-14。通过测量剩余的碳-14，科学家可以估算自死亡以来经过的时间。
¹⁴C → ¹⁴N + β⁻
6. The Half-Life of Carbon-14 | 碳-14 的半衰期
The half-life of carbon-14 is about 5730 years. This means that after 5730 years, half of the original carbon-14 atoms have decayed. After another 5730 years, half of the remaining half has decayed, leaving one quarter.
碳-14 的半衰期约为 5730 年。这意味着经过 5730 年后，原有碳-14 原子的一半已经衰变。再经过 5730 年，剩余一半中的一半又衰变，剩下四分之一。
N = N₀ × (1/2)t/t½
In this equation, N is the remaining amount of carbon-14, N₀ is the original amount, t is time and t½ is the half-life. Because the half-life is short, carbon-14 dating works best for fossils up to about 50,000 years old.
在该方程中，N 是碳-14 的剩余量，N₀ 是原始量，t 是时间，t½ 是半衰期。由于半衰期较短，碳-14 定年最适用于大约 5 万年以内的化石。
7. Why Only Some Remains Fossilise | 为什么只有部分遗骸形成化石
Fossilisation is rare because several chemical conditions must be met. The remains must be buried quickly to reduce oxygen and bacterial decay. The surrounding water must carry suitable dissolved minerals, and the pH must allow precipitation.
化石形成十分罕见
Published by TutorHao | KS3 Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图