Palaeozoic: 'Factmonster.com' Earth's Geological Timeline
It is now generally assumed that planets are formed by the gathering and binding of gas and dust in a cosmic cloud, but there is no way of estimating how long this process takes. Our Earth acquired its present size, more or less, between 4,000 million and 5,000 million years ago. Life on Earth originated about 2,000 million years ago, but there are no good fossil remains from periods earlier than the Cambrian, which began about 550 million years ago. The largely unknown past before the Cambrian Period is referred to as the Pre-Cambrian and is subdivided into the Lower (or older) and Upper (or younger) Pre-Cambrian—also called the Archaeozoic and Proterozoic Eras. The known geological history of Earth since the beginning of the Cambrian Period is subdivided into three giant chunks of time, or eras, each of which includes a number of shorter periods. They, in turn, are subdivided into
even shorter subperiods. In a subperiod, a certain section may be especially well known because of abundant fossil finds. Such a section is called a formation, and it is usually identified by a place name.
[http://www.factmonster.com/]
Palaeozoic: In Context
Scientists have divided the time that has passed since the beginning of earth's history into four time periods. These time periods are called eras. The first era is called the Azoic Era, the second era is the Palaeozoic Era, the third era is the Mesozoic Era, and the fourth era is the Caenozoic Era. It is important to understand the following eras in order to understand the progression of evolution.
[http://www.eng.iastate.edu/]
Palaeozoic: History of the Earth
Exploring this series of exhibits will take you on a journey through the history of the Earth, with stops at particular points in time to examine the fossil record and stratigraphy.
[http://www.ucmp.berkeley.edu/]
