The original meaning of the Critical Zone (CZ) was spatial and pointed to one physical referent: the terrestrial surface of the entire Earth. As usage increased among researchers in the geosciences, social sciences, and humanities, new meanings led to the concept pointing to different places and ideas. Emerging trends have expanded the CZ further: CZs are mapped in computational spacetime and on distant planets and asteroids. The polysemous character of the CZ can be confounding for a field-based science, but Earth scientists and technologists have collaborated to collect and harmonize Big Data sets into a sizable library of CZ research in a short time (around 20 years). In this review, we map the semantic range of the CZ and explore how CZ science has remained coherent even as researchers diversified the concept by developing distinguishable but loosely overlapping meanings. We organize extant meanings into three tiers: (1) Earth’s spatial interface of the geochemical and biological; (2) scientific knowledge of geophysical functionality of the CZ, as represented in an ever-growing library of data or by a single feature as proxy (e.g. soil); (3) a planetary home vulnerable to human disruption. In a time of immense human influence on the CZ, we underscore the latent meaning of planetary home, which marshals motivations of care and protection. These three tiers—the ontological, epistemic, and anthropocenic—build on each other to make the CZ a uniquely valuable concept for navigating the socio-ecological challenges of the Anthropocene.

临界区 (CZ) 的原始含义是空间性的，指向一个物理参照物：整个地球的陆地表面。随着地球科学、社会科学和人文学科研究人员的使用增加，新的含义导致这个概念指向不同的地方和想法。新兴趋势进一步扩展了 CZ：CZ 被映射到计算时空以及遥远的行星和小行星上。CZ 的多义性特征可能会混淆基于领域的科学，但地球科学家和技术专家已合作在短时间内（大约 20 年）收集大数据集并将其整合到一个相当大的 CZ 研究库中。在这篇评论中，我们绘制了 CZ 的语义范围，并探索 CZ 科学如何保持连贯性，即使研究人员通过开发可区分但松散重叠的含义来使概念多样化。我们将现存的意义分为三个层次：（1）地球的地球化学和生物空间界面；(2) CZ 地球物理功能的科学知识，以不断增长的数据库或单个特征作为代表（例如土壤）表示；(3) 一个容易受到人类破坏的行星家园。在人类对 CZ 产生巨大影响的时代，我们强调行星家园的潜在意义，它调动了关怀和保护的动机。这三个层次——本体论的、认知的、