Geology is the scientific study of the origin, history, and structure of the Earth based on observable data and the principle of uniformitarianism. Observable data can be qualitative descriptions or quantitative measurements. In the 17th century, Irish Bishop James Usher estimated the age of the Earth to be around 4004 BC based on biblical accounts, but in the 18th century, Scottish geologist James Hutton developed the principle of uniformitarianism from his observations of rock formations. Modern geology uses both relative dating methods based on principles like superposition and cross-cutting relationships, as well as absolute dating techniques like radiometric dating to determine ages of rocks and the Earth in the billions of years.

1. Geology and Why it Rocks

2. 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.

6. 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?

7. 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

8. 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

10. Common Relative Age Relationships 1.) Superposition: A relationship where the younger rocks are superimposed on the older rocks. A is Older than B

11. 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.

12. 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.

13. 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.

14. 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