Arthur’s Seat, Edinburgh, Scotland Debbie Amato

4. Arthur’s Seat, Edinburgh, Scotland Debbie Amato

5. Geology and the Methods of Science Basic Assumption: The Earth works in an orderly fashion in which natural phenomenon will recur given the same set of conditions. 1. Question: We want to know how some part of the Earth works. 2. Data Collection: Observe, measure, describe, compile. 3. Hypothesis! A logical but tentative explanation that fits all the data collected and is expected to account for future observations as well.

6. 4. Testing. Testing, testing, and more testing. 5. Modification. Hypotheses are modified to include the results of testing (see #4). 6. Theory! The hypothesis now withstands rigor of all the testing (see #4) and consistently explains accumulating data to become a THEORY. A theory is a generally accepted explanation for a given set of data or observations. 7. Testing. The theory is tested, tested and tested again. 8. Scientific Law! If a theory meets rigorous testing over a long period of time it may become a SCIENTIFIC LAW. 9. Principle. Generally a scientific law so fundamental to geology that it provides the foundation of the science.

7. GEOLOGICAL CONCEPTS 1. Catastrophism - Observations led to the belief that the Earth developed through a series of upheavals that were relatively short-lived. A hypothesis that was proven inadequate and discarded.

8. Through Geology, we have learned that the Earth is very old (4.6 billion years). So…. Time, time, time is on my side, yes it is.

9. Siccar Point, Scotland

10. 2. Principle ofUniformitarianism - James Hutton discovered that Earth processes acted over a long period of time (1830s). Hutton proposed that the physical, chemical and biological processes observed on a daily basis, have also acted on the Earth over very long periods of time. Observations of current geological processes could be used to interpret the rock record of very old geologic events. BIRTH OF MODERN GEOLOGY

11. Other Important Geologic Principles Superposition - The scientific law stating that in any unaltered sequence of rock strata, each stratum is younger than the one beneath it and older than the one above it, so that the youngest stratum will be at the top of the sequence and the oldest at the bottom.

12. Principle of Original Horizontality - The scientific law stating that sediments settling out of a fluid (air and water) are deposited horizontally or nearly horizontally in layers that lie parallel or nearly parallel to the Earth’s surface. Photo by Kevin Hefferan Badlands National Park

13. Principle of Cross-Cutting Relationships - The scientific law that states an igneous intrusion or geologic structure is always younger than the rock that surrounds it.

14. Siccar Point, Scotland

15. Siccar Point, Scotland

16. Principle of Inclusions - The scientific law stating that rock fragments contained within a larger body of rock are always older than the surrounding body of rock.

17. So… Where do we begin our study of The Earth ?

18. The Creation of the Solar System Begin with the “Big Bang” approximately 12 billion years ago. Space expanded rapidly and then began to contract. As temperatures cooled, Hydrogen and Helium gases formed. Denser pockets of gas condensed further due to gravity. Accumulations became galaxies. Began to rotate to form disc-shaped clouds. Center collapsed to form the Sun. As heat increased in the Sun, particles were blown away as “solar wind”. Particles collided and accreted becoming planetesimals.

19. So how did we get to here? As larger and larger particles collided, larger planetesimals were formed. Some of these continued to collide and the largest became the planets, while the smaller ones may have become moons. Intense solar radiation heated the closest planets causing the lighter elements to be vaporized and blown out into space. This concentrated the heavier elements like iron and nickel on the inner planets and the lighter elements on the outer planets.

20. The Earth’s Earliest History Beginning of the Earth was extremely violent. Grew by planetesimal impact. Became very hot, heated to the melting point of iron. Innermost rocks began to become compressed, so more heat. Radiogenic heat was added due to radioactive fission. Earth underwent differentiation into layers.

22. Early Differentiation of the Earth What was the Earth’s early composition? Need to consider meteorites that have struck the earth to get an idea of composition. Most are iron and nickel. Some contain chondrules. Small rocky bodies within the meteorites that may represent matter condensing from the original solar nebula. Earth’s composition should be similar to these meteorites. However - Meteorites are 35 % iron, while Earth’s surface rocks only 6 %.

23. Early Differentiation of the Earth Where did the iron go? As Earth was still accreting, temperature rose above melting point of iron. Iron liquified. Because of higher density, iron sank into the proto-Earth’s center due to gravity. Lighter elements rose to the surface. Originally, Earth was homogeneous. Due to heat and melting, Earth materials separated forming concentric zones of differing density. Thus, Differentiation.

24. Differentiation and the Earth’s Interior

25. Earth’s Interior Three Principal Layers Each has different Composition and density (mass/volume). CRUST - Outermost layer Density = low Composition is silicon and oxygen-based minerals and rocks. Crust is extremely thin. Consistency is rocky. Composed of two general types. Continental crust Oceanic crust

26. Earth’s Interior Three Principal Layers Each has different Composition and density (mass/volume). CRUST - Outermost layer Density = low Composition is silicon and oxygen-based minerals and rocks. Crust is extremely thin. Consistency is rocky. Composed of two general types. Continental crust Oceanic crust

27. Earth’s Interior MANTLE - Middle thin layer Density = medium Composition is silicon and oxygen-based but also includes iron and magnesium. Consistency is plastic. Contains two parts, Upper and Lower Mantle. CORE - Inner layer Density = high Composition is primarily iron and nickel. Contains two parts Inner core is solid. Outer core is liquid.

28. Subdivisions of the Earth’s Interior Within these three principal layers are subdivisions. Crust consists of OCEANIC CRUST (brown) CONTINENTAL CRUST (green). Oceanic crust is thin (8-10 km), dense, and found below ocean basins (blue). Continental crust is thicker (20-70 km), has low density and forms the bulk of continents. The crust rides on the very upper most portion of the mantle.

29. The outermost sublayer is the most active geologically. Large scale geological processes occur, including earthquakes, volcanoes, mountain building and the creation of ocean basins. Contains parts of the upper mantle and all of the crust. Called the LITHOSPHERE (rock layer).

30. Lithosphere is a strong layer, but brittle. Represents the outer approximately 100 km of the Earth. Thicker where continents exist, thinner under oceans. Below the lithosphere resides the ASTHENOSPHERE (weak layer).

31. Asthenosphere is part of the upper mantle. Asthenosphere is heat softened and acts like a plastic. It is weak, slow flowing, yet solid rock. (Things that make you go, hmmm.) Generally 100 to 350 km beneath Earth’s surface.

32. Overlying the lithosphere is the ATMOSPHERE. Composed of gases released during volcanic eruptions and from plant respiration.

33. Outgassing from volcanoes also helped produce the water in the Earth’s ocean basins. Led to the initial development of the HYDROSPHERE. Together, the Lithosphere, Atmosphere and Hydrosphere support the BIOSPHERE.

34. Earliest atmosphere was comprised of H, He, ammonia (NH4) and methane (CH4). Combination was deadly to life as we know it. Modern atmosphere is composed of: Nitrogen (N) 79% Oxygen (O) 20% Argon (Ar) 1% All other gases <1% Atmosphere protects us from a variety of dangerous particles.