GeologyRocks

What is A Mass-Extinction?

What Is A Mass-Extinction?

An extinction event is defined as a sharp decrease in the number of species over a short period of time. A mass extinction is further defined based on four points, pattern, duration, breadth and magnitude, and the event must:

• be confined to a short period of geological time
• Affect a wide variety of clades, that occupy a wide range of Habitats
• And eradicate a high proportion of species.

Geological history of UK - Part 1

This slideshow covers the history of the UK from the Cambrian (550 Million years ago) to the Devonian (360 Million years ago).  read more »

Geological Time

How do we know the age of the Earth? How do we know the age of rocks we find? There are two main ways to date rocks - absolute dating and relative dating. After the rocks have a date assigned to it, they can be put in some sort of order, and the relative dates worked out. This is the geological timescale.

The Ageing Earth

Introduction to the Geological Features of the Moon

The Moon is the only natural satellite of the Earth and formed at about the same time, over four and a half billion years ago, but has not evolved in the same way. Lacking an atmosphere, water and life, and having cooled more rapidly due to its smaller size, much of the surface has not been changed significantly for billions of years.

Introduction to Carbonates

Carbonates are rocks composed mainly of calcium carbonate, CaCO₃. Some examples of common carbonate rocks are limestones and chalk. Carbonates form by precipitation from water; either straight from the water, or induced by organisms, to make their shells or skeletons, and they form in many environments (Figure 1).

Introduction to Sedimentology

Sedimentary rocks are made by the accumulation of particles of older rocks, either as clasts (chunks of rocks) or as mineral grains, chemically or biogenically precipitated. Clastic sedimentary rocks are principally classified on the basis of grain size and then further divided in terms of mineralogy. One of the most important things sedimentary rocks can tell us about is palaeoenvironments - ancient environments. This is done by looking at the sedimentary structures and the fossils contained within the rocks.

Introduction to Metamorphic Petrology

Metamorphic petrology is the study of rocks which have been changed (metamorphosed) by heat and pressure. They are broadly categorized into regional and contact. Metamorphism is an extension of the process which forms sedimentary rocks from sediment: lithification. However, all types of rocks; igneous, sedimentary and metamorphic, can all be metamorphosed. During metamorphism no melting takes place. All the chemical reactions which take place occur in the solid-state.

Introduction to Igneous Petrology

Igneous rocks are formed form the cooling of molten rock, magma. They are crystalline, which means they are made up of crystals joined together. There are many different types of igneous rocks but they fall into two (very) broad categories; intrusive and extrusive. Intrusive rocks are igneous rocks which form at depth. They cool slowly, taking tens of thousand of years to cool. They have large crystals, tens of millimetres in size. Extrusive rocks are those which have erupted from volcanoes.

Plate Tectonics: An Introduction

Plate tectonics is the theory that underpins most of modern geology. The basic idea is that the surface of the Earth is made up of several segments - plates. These plates move around the globe while being created and destroyed at their margis. This theory helps to explain many things, such as the rock types that indicate desert climates in north England. Rather than have to move the climatic belts, it is the continent itself that has moved.

An Introduction to Structural Geology

Structural geology is the study of the features formed by geological processes. Features include faults, folds and dipping strata. Geologists can work out the order of events and see which events are related by taking fairly simple measurements and using simple methods.