Two methods of dating rocks


21-Jun-2018 08:42

Continental lithosphere, because it is less dense, is more bouyant and is not easily subducted, or recycled back into the Earth's interior.

As a result, continents are made-up of very old rocks, some dating back 3.8 billion years.

The study of paleogeography has two principle goals.

The first goal is to map the past positions of the continents.

The Earth's magnetic field has another important property.

Like the Sun's magnetic field, the Earth's magnetic field "flips" or reverses polarity.

Fluctuations, or "anomalies", in the intensity of the magnetic field, occur at the boundaries between normally magnetized sea floor, and sea floor magnetized in the "reverse" direction.

The past positions of the continents during the last 150 million years can be directly reconstructed by superimposing linear magnetic anomalies of the same age.Certain kinds of rocks form under specific climatic conditions.For example coals occur where it is wet, bauxite occurs where it is warm and wet, evaporites and calcretes occur where it is warm and dry, and tillites occur where it is wet and cool.Less extensive mountains can also form when continents rift apart (e.g.

East African Rift), or where hot spots form volcanic uplifts.The ancient distribution of these, and other, rock types can tell us how the global climate has changed through time and how the continents have travelled across climatic belts.In order to reconstruct the past positions of the continents it is necessary to understand the development of the plate tectonic boundaries that separate continents and bring them back together again.The past distribution of plants and animals can give important clues concerning the latitudinal position of the continents as well as their relative positions.