UNIT 6 HISTORICAL GEOLOGY CHAPTER 12

Think about it. What is the history of YOU? Most stories you tell or memories you have exist in relation to other events in your life. “Remember that one time…..” “Back when we used to……” “What plans do you have for….” “When was that....” “I can’t wait until…”

Well Earth is the same way! Earth has it’s own history which can be pieced together by interpreting past occurrences.

The Rock Record Geological Time Scale Dividing the Earth’s history into sections based on the fossils and rock evidence.

The book of the world: If you were to write a history of the Earth’s past, allowing just one page per year, your book would be 4,600,000,000 pages long. That’s a very thick book — 145 miles to be exact. An average reader, reading about 1 page every 2 minutes would need more than 17,503 years to finish it. And that’s with no time out for anything else — no time to eat, sleep, ride a bike, or go to school. Even if you were an amazing speed reader and could read 2 pages every second, it would still take you nearly 73 years to read the entire book.

Earth is estimated to be 4.6 billion years old (byo) To study Earth’s history, geologist use 3 main ideas The rock record provides evidence of geological events and life forms of past Processes observed on Earth today are as same as in past Earth is very old and has changed over time

2. What is uniformitarianism 2. What is uniformitarianism? States that the physical, chemical and biological laws that exist today were the same in the geologic past Ex: weathering, erosion, oxidation, lithification, volcanos, earthquakes, mountain building

Shaded area represents how much of Earth’s history has no physical record!!

3. What is relative dating? Geologist put events in chronological order w/o assigning an exact age Superposition – in an undisturbed sedimentary rock layer, each layer is older than the one above it Original horizontality– layers of sediment put down in horizontal layers Cross-cutting– a fault, or magma intrusion is younger than the layers it cuts across

LAW OF SUPERPOSITION

PRINCIPLE OF ORIGINAL HORIZONTALITY

PRINCIPLE OF CROSSCUTTING

Crosscutting relationships

Put in order from oldest to youngest H R M F B I Put in order from oldest to youngest

4. Geologist interpret rock layers using Unconformities – a surface that shows a break in the rock record, usually due to erosion Inclusions –rock layer is younger than inclusion that contains it Correlations – matching rock layers of similar age in different locations.

Inclusions

A Record of Uplift, Erosion, and Deposition Makes no sense without caption in book

CORROLATION AT 3 LOCATIONS

Where can you find the oldest rocks on Earth?

WHAT IS THE FOSSIL RECORD? A RECORD OF PAST LIFE ON EARTH

5. Two things must happen for fossils to be preserved– rapid burial and possession of hard parts. All fossils are preserved in sedimentary rocks. Why? Remains would be destroyed by heat and/or pressure in igneous and metamorphic rocks. //www.youtube.com/watch?v=p8xCmciGALA

Think about it….how do we know that 99% of all living things that have ever lived on Earth have gone extinct? THE FOSSIL RECORD! 5. Two things must happen for fossils to be preserved rapid burial and possession of hard parts. All fossils are preserved in sedimentary rock. Why?

https://www.youtube.com/watch?v=5qTheYdwd9Q

How can we use fossils to determine the age of rocks around them How can we use fossils to determine the age of rocks around them? We can use fossils to correlate rock layers and determine their sequence (what came before and after)

6. There are several types of fossils Petrified fossils – remains have turned to stone, replaced by minerals Molds and casts – create imprints and shapes of organisms Carbon films – all liquids and gas squeezed out of organism leaving only carbon film Trace fossils – indirect evidence of past life; footprints, burrows, coprolites

Types of fossils

Petrified Fossils

Molds and casts Carbon film

Trace fossils Unaltered remains

Evolution of horses From the Fossil record

7. Define the following terms Extinct – organism that no longer exists on Earth Fossil – preserved remains from geologic past Principle of fossil succession – fossils succeed one another in definite order Theory of evolution – life forms have changed over time from simpler to more complex

e. Natural selection – organisms better adapted to environment most likely to survive and reproduce f. Index fossil – used to correlate fossil record; must be geographically widespread and abundant, but only existed for short period of time

Using index fossils Index fossils act as a reference point when dating rock layers. Like a “you are here” symbol on a map Or index words in the dictionary

Which 2 layers were formed at the same time? HOW CAN YOU TELL?

Dating with radioactivity 8. During radioactive decay, unstable nuclei spontaneously decay (break apart) releasing energy.

Common Types of Radioactive Decay Makes no sense without caption in book

In radiometric dating, scientist measure the ratio b/t radioactive parent and more stable daughter isotope. ↑daughter = older sample Radioactivity – process by which atoms decay Half life – time it takes for ½ of parent isotope to decay

Dating organic materials When an organism dies, the amount of C14 decreases as it decays. By comparing ratio of C14 to N14 radiocarbon dates can be found Radiometric dating – calculates absolute age of rocks and minerals Radiocarbon dating – method to date organic materials using C14

How C14 dating works

The geologic time scale includes both geologic events and major developments in evolution of life on Earth 11. What is geologic time? Is a timeline that divides Earth’s history in units representing specific intervals of times. (like a calendar divides time into months, weeks, and days)

12. Intervals of time Eons – longest, lasting billions of years; there have only been 4 eons on Earth Eras – lasting hundreds of millions of years; there are 3 eras Periods – lasting 10’s to 100’s of million of years; there are 13 periods Epochs – most recent times; smallest unit lasting 10’s of millions to 100’s thousands

13. What usually marks the end of one era or period and the beginning of another? Catastrophic event such as asteroid impact Environmental changes Life forms rising and/or going extinct