相对年代测定是通过沉积岩层的层序、原始构造、不整合、穿插构造（cross -cutting- structures）和陨石坑来确定的。新的岩层沉积在较老的岩层之上。因此，如果它们没有被褶皱或断层扰乱的话，岩层的相对年代可以由它们在层序中的位置确定。

相对年代测定是通过沉积岩层的层序、原始构造、不整合、穿插构造（cross -cutting- structures）和陨石坑来确定的。

新的岩层沉积在较老的岩层之上。因此，如果它们没有被褶皱或断层扰乱的话，岩层的相对年代可以由它们在层序中的位置确定。

原生构造是在岩石沉积时形成的，有些可以用来确定相对年代。它们包括交错层理、粒级层、波痕、化石和枕状熔岩等。交错层理可以由风或地下水流所形成，交错层理的角度可以从水平到40°。侵蚀作用可削平这些层的顶部，使之呈截顶状。但交错层理的底层一般平行于层的底面。这样，交错层截顶面与其上交错层切线的相对位置，可用来建立某一沉积岩系的相对年代。而且交错层的凹面一般面向新层（顶部）。在粒级层中，从一个单层的底到顶，其粒级出现由粗到细的变化。粒级层是由间歇性的海底底流形成，最常见的是由浊流而成。浊流是携带沉积物的高密度水体。水流沿斜坡急速奔流而下，当水流变缓时，粗粒物质首先沉积，小的颗粒依次沉积。因此，在一个层中的粒级向顶面逐渐变小。

在很多沉积岩序列里 ， 不是所有的原始沉积物都能保存下来。上升可以形成侵蚀面，然后又被新沉积物所覆盖，这种埋藏的侵蚀面称为不整合（unconformity）。可以用它来确定地层的相对年代。主要的不整合有非整合（nonconformity）、角度不整合（angular unconformity）、 平行不整合（disconformity）和小间断（diastems）。非整合是指沉积岩覆盖在较老的变质岩或深成火成岩之上。角度不整合将年轻的、变形较轻的沉积岩同倾斜或褶皱的沉积岩分开，不整合面上、下两层之间有一角度差异。平行不整合是基本上互相平行的岩层之间有起伏不平的埋藏侵蚀面。如果化石证明两岩层在时代上有明显差别，则可判定在该两层之间曾有间断发生。沉积作用的这种短期间隔，称为小间断或沉积间断。

穿插火成侵入岩（如岩脉、岩株和岩基）总是比被它们所侵入的最新岩层还要年轻，而比不整合覆盖在它上面的最老岩层要老。如果两个侵入岩接触 ， 火成侵入岩的相对时代由穿插关系也可确定，一般是年轻的侵入岩脉穿过较老的侵入岩。若岩层沿断层发生了位移 ，其移动的相对时间也可以确定。断层的最后位移必然是出现在因断层而错位的最新岩层沉积之后，又在不整合覆盖断层的最老岩层沉积之前。

同样，岩系褶皱的时代总是要比受褶皱的最年轻岩层晚，而比未褶皱的、盖在上面的最老岩层早。一个岩系变质的时代总是比变质的最年轻岩层要晚，而比覆盖在上面未遭受变质的最老岩层要早。

生物的演变是从简单到复杂，从低级到高级，不断进化和发展的。因此，一般说来，地层年代越新其中含生物就越进步、越复杂。另一方面，不同时期的地层中含有不同类型的化石及其组合，而相同时期且在相同地理环境下所形成的地层，不论相距多远都含有相同化石或化石组合。

根据生物组合面貌可以反推地层的大概年龄，经过长年研究，古生物学家筛选出一系列化石或化石组合作为标准化石，用之确定地层时代，如笔石类常作为奥陶、志留纪的标准化石。

沉积岩中的碳酸钙浓度，在年代上表现出了明显的周期性。

Relative dating, which is less precise than absolutedating, yielding estimated age only in terms ofwhether the specimen/site of interest is older oryounger than another specimen/site of a morefirmly determined age.

Important relative dating techniques include:

Stratigraphic analysis (or, stratigraphy) – This is a basic, fundamental aspect of the archaeological,or paleoanthropological, analysis of a site. Stratigraphic analysis of a siteinvolves documenting the layering ofgeological sediments, one on top ofanother (in what archaeologistsrefer to as a “sediment column”, or“stratigraphic horizon”), andestablishing (and mapping) therelative placement of anystratigraphic level(s) containingarchaeological orpaleoanthropological materialwithin the order that geologicdeposits were laid down. Stratigraphic analysis employs abasic principle known as the Law of Superposition ‐‐sediments that lie at the lowestlevels of a sediment column areassumed to be the oldest, whileoverlying sediments higher inthe sediment column areinterpreted as being younger(as they were deposited after,and on top of, the olderunderlying sediment strata). For example, if an artifact or fossil was found under a stratum (i.e.,layer) of volcanic ash sediments, the volcanic ash deposit could bedated using the argon‐argon absolute dating technique. Thiswould serve as a reference point for the relative dating of theartifact/fossil found in a sediment layer below the volcanic ash.That is, based on the Law of Superposition, the artifact/fossillying below the volcanic ash would be interpreted as being olderthan the absolute age that was determined for the ash layer (inthis case, the volcanic ash layer could be said to act as a markerbed in the interpretation of the site).

Biostratigraphy (or, faunal correlation) –This relative dating technique makes use of faunal (i.e., animal) fossilremains to infer an approximate age for a site (e.g., a hominin site). As many fossil animal species as possible are identified (and someparticular fossil lineages, such as pigs and elephants, are especiallyuseful because fossil species in these lineages are both very distinctive intheir morphology and occur only in certain stages of the fossil record ‐‐that is, they have relatively “short” evolutionary occurrences).Then, knowledge of the temporal occurrence of those fossil species isused to arrive at an estimated span of time where all those fossil specieswould be found together at a given site. This gives the possible age range for the site. The form and/or style of artifacts (such as stone tools orpottery) can also be used as a relative indicator of age.This is done using a technique known as seriation.