When a rock crystallizes from melt (magma and/or lava), it is an igneous rock.

principles of relative dating in geology-32principles of relative dating in geology-45

Principal of Superposition: - In an undisturbed sequence of rocks, each layer is younger than the one beneath it and older than the one above it. Faunal Succession: - Fossils as timepieces - Use of index fossils to correlate rocks (formations) from different locations. Unconformities: - Markers of missing time - (deposition of rocks isn’t continuous forever) a) Disconformity: an unconformity in which the rocks above and below the unconformity are parallel.

b) Angular Unconformity: not parallel due to folding and uplifting, erosion then takes part of the rock away, and new layers form on top of the unconformity.

For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.

By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.

Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.

Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.

We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!

Imagine that you're a geologist, studying the amazing rock formations of the Grand Canyon.

The basic principles of Relative Time are Uniformitarianism (the present is the key to the past and everything assumes a uniform or constant rate of change) and Actualism (the present is the key to the past and everything assumes a variable rate of change).

There are five principles of Relative Dating: Unconformities are a gap or break in the rock sequence that represents time.

101 – 1st Edition Lecture 16 Outline of Last Lecture I. Geological Time [Intro] Outline of Current Lecture I. Absolute Dating Current Lecture Stratigraphy: the description, correlation, and classification of strata in sedimentary rocks.