Understanding Earth History and Geological Principles

Understanding the Earth and Its Past

Geology is the science that studies the Earth, its structure, and its component materials, as well as its origin, history, and the changes occurring within it. Geology seeks to understand how the planet works. From a more pragmatic perspective, geology is concerned with practical issues such as locating oil reserves, finding the best sites for water wells, determining suitable land for dam construction, and identifying mineral deposits like iron.

Reading the Rocks

• The Earth is immensely old.
• The Earth is constantly changing.
• Rocks are the archives of the Earth.

Geological Scales

• The Time Scale
• The Spatial Scale

Reconstructing the Earth's History

Rebuilding a story, whether it is the history of the Earth, a country, or a person, basically involves two kinds of activities:

• Investigating the events.
• Ordering these events chronologically.

Discovering Past Events

• Ecological events generate changes.
• Changes leave marks or evidence.
• New materials originate.
• Geological structures result from these processes.
• Features like ripple marks are formed.

The Principle of Uniformitarianism

Interpreting these tracks is only possible if a specific geological process, occurring at different times and places, causes similar signs. The principle of uniformitarianism argues that the processes occurring at present are the key to interpreting what happened in the past.

Geological Dating Methods

Once you understand how geological events have occurred in a particular area, it is necessary to establish a temporal order to reconstruct the story using:

• Relative dating
• Absolute dating

Fundamentals of Stratigraphic Dating

• Principle of original horizontality of strata
• Principle of lateral continuity of strata
• Principle of superposition of strata

Ceiling and Wall

The modern top layer of a stratum is called the ceiling. The base of a stratum is the wall. The average vertical distance between the ceiling and the wall of a layer is called its thickness (or power).

Criteria of Polarity

The superposition principle is sufficient to order a set of layers that maintains its original horizontality. In these cases, we use the criteria of polarity to determine the chronological sequence.

Conformity and Unconformity

It is said that two materials are conformable (consistent) if the surface that separates them is parallel to the bedding planes of both. Otherwise, the relationship is considered unconformable (discordant).