Geology and Why it Rocks

Geology: A scientific study of origin, history and structure of the earth based on observable qualitative and quantitative data and grounded the principle of uniformitarianism.

Observable: A quantity that can, in principle, be measured.

Qualitative Observation: You express the phenomenon you are trying to describe using some non-numerical value. Example: The rock is more dense than water but less dense than gold.

Quantitative observation: You actually come up with a numerical value to express the phenomenon you are trying to describe. Example: The rock has a density of 6 g/cm3.

Uniformitarianism: The concept that much of geology is dependant upon. Uniformitarianism holds that the physical phenomena that we observe in the earth today must have happened in the past and will continue to happen into the future.

Irish Bishop James Usher- In 1645 meticulously goes

through the old testament, generation by generation to try to determine the age of the earth.

-He determines that the earth was created on October 24, 4004 B.C. at precisely 9:00 am.

How Old is Our Earth?

Relative Age: A is older than B. A qualitative observation of the age of something.

Absolute Age: A is 15 million years old. A quantitative observation of the Age of Something

Jim Hutton’s Relative age Breakthrough

James Hutton: 1726-1797

-Known as the Father of Geology

-Came up with the concept of Uniformitarianism

-In 1780 has a breakthrough while looking at rocks on Siccar Point, Scotland

Common Relative Age Relationships

1.) Superposition: A relationship where the younger rocks are superimposed on the older rocks.

A is Older than B

Common Relative Age Relationships

2.) Original Horizontality: Rocks are deposited in horizontal layers, which means that tilting must happen after the rocks formed.

A is Older than B. Both A and B are older than the process that tilted them.

Common Relative Age Relationships

3.) Cross-Cutting: A type of rock is first deposited horizontally. A second type of rock then intrudes into this rock’s space. The intruder is the younger rock.

A is Older than B.

Common Relative Age Relationships

4.) Inclusions: A type of rock is initially deposited. Pieces of that rock are then broken off by erosion and incorporated into a newer, younger rock.

A is Older than B.

Modern Absolute Dating Using Radioactivity

-1950s: Scientists figure out how to determine an absolute age for ancient rocks using the radioactive decay of the Uranium atom.

-Current absolute age of the earth is approximately 4.5 billion years, from dating the Uranium in Zircon minerals