Relative dating techniques are methods used by scientists to determine the chronological sequence of events in Earth's history without necessarily determining their absolute age. These techniques are based on the principle that older layers or objects are buried beneath younger ones. Here are some of the main relative dating techniques:

1. Stratigraphy: This is the study of rock layers (strata) and their sequence. The principle of superposition states that in undisturbed strata, the oldest layers are at the bottom, and the layers become progressively younger toward the top.

2. Biostratigraphy: This technique uses the presence of fossilized remains of plants and animals to correlate the ages of rock layers. Different species of fossils appear and disappear in the geological record in a predictable order, allowing scientists to use them as markers.

3. Cross-cutting Relationships: This principle states that any geological feature (like a fault or an intrusion) that cuts across another feature must be younger than the feature it cuts through.

4. Inclusions: Fragments of one rock type enclosed within another are known as inclusions. The rock containing the inclusion must be younger than the inclusion itself.

5. Faunal Succession: This principle is based on the observation that fossil assemblages (groups of fossils) succeed one another vertically in a specific, reliable order that can be identified over wide horizontal distances.

6. Lateral Continuity: This principle states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. If a layer is observed in two separate locations, it can be assumed that the layer was originally continuous and has been disrupted by processes like erosion or faulting.

7. Lithostratigraphy: This involves the correlation and relative dating of rock strata based on their physical and lithological (rock type) characteristics.

8. Fluorine Dating: This technique compares the accumulation of fluorine in bones from the same site. Bones absorb fluorine from groundwater over time, so older bones have more fluorine compared to newer ones.

9. Tephrochronology: This technique uses discrete layers of volcanic ash (tephra) from a single eruption to create a chronological framework for dating events.

These relative dating techniques are crucial in fields like geology, paleontology, and archaeology, helping scientists to piece together the history of Earth and its life forms.