Lecture 2 - Geologic Time PDF

Lecture 2 – Geologic Time Quaternary (5 kya) Mesozoic (66 mya) Paleozoic (252 mya) Precambrian (541 mya) Albert Heim – Father of Applied Geology 1 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Announcemen...

Lecture 2 – Geologic Time Quaternary (5 kya) Mesozoic (66 mya) Paleozoic (252 mya) Precambrian (541 mya) Albert Heim – Father of Applied Geology 1 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Announcement: Mineral & Rock ID Kits Labs begin this week with a look at mineral ID. If you would like to purchase a mineral and rock ID kit for the labs, Dawson Club is selling them for $40. You can purchase one via the following link: https://forms.gle/bWUDpcqk4tepXxVbA Note that you do not need to purchase a kit as we will have these available for use and sharing in the labs. This is only if you would like your own personal kit. 2 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Announcement: Reminder of Labs Section Location Day Start Time End Time L1A EOS-M 107 Wed 17:00 19:00 L1B EOS-M 107 Fri 16:00 18:00 L1C EOS-M 107 Tue 16:00 18:00 L1D EOS-M 107 Fri 8:00 10:00 L1E EOS-M 107 Wed 13:00 15:00 L1F EOS-M 107 Thu 16:00 18:00 L1G EOS-M 107 Thu 13:00 15:00 L1H EOS-M 107 Fri 10:00 12:00 L1I EOS-M 107 Tue 14:00 16:00 L1J EOS-M 107 Wed 9:00 11:00 3 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Announcement: Office Hours My office hours begin this week: Location: EOS-Main (EOSM) 323 Time: Wednesdays 2-3 PM If the time doesn’t work feel free to schedule another time during the week 4 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  iClicker: Warm-Up Question Which of the following statements do you think is TRUE? A) You can find ancient coral reefs at the top of the Rocky Mountains. B) You can find ancient coral reefs buried 2000 m deep under Alberta. C) The rocks of the Canadian Shield are more than 4 billion years old. D) The land mass on which UBC-Okanagan sits (Kelowna) used to be separated from the continent similar to Vancouver Island today. E) All of the above are true. 5 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Today’s Lecture: Probing Question Is there a reason why we find potash in Saskatchewan, oil in Alberta, natural gas in eastern BC, and copper and gold in western BC? 6 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Canada & Geologic Time 7 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Changes on a global scale are small, but when seen over geological time…are substantial Approx 200 million years to present 8 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Lecture Goals – Geologic Time By the end of this lecture, you will be able to: 1) Recognize that the geologic processes we see today have acted over very long timescales and can provide us with clues about the processes that shaped the Earth in the past. 2) Apply relative dating principles to interpret the geologic history at an engineering project site. 3) Compare and contrast relative and absolute dating methods. Apply basic half-life calculations for absolute dating. 4) Describe what the major divisions of the geologic timescale signify. 9 of 38 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 How do We Know Things…? Geocentric heliocentric Earth is at Sun is at center center 10 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Should We Question…Everything? … 11 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Science in the 18th Century: The ‘Enlightenment” Epistomology: The philosophy of knowledge - How can we really know something? From faith From intuition From authority From observations - The Scientific Method Hypothesis: An explanation that accounts for a set of observations and can be tested by further investigation 12 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Geology in the 18th Century Catastrophism: … points to disasters (e.g. floods or earthquakes) to explain features of the earth’s surface, such as mountains and valleys. … also used to account for the many "funny looking bones" found in rock linking these with religious doctrine (e.g. the Flood story and Noah’s Ark). * Archbishop Usher's declared in 1658 that the Earth was begat on Sunday, October 23, 4004 B.C. at precisely 6:00 a.m. 13 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Uniformitarianism … the principle that “wouldn’t go away” Suggests that geological processes now operating to modify the Earth's surface must have acted in much the same manner and with essentially the same intensity throughout geologic time, and that past geologic events can be explained by forces observable today. James Hutton "The present is the key to the (1726-1797) past“ 14 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Uniformitarianism The application of uniformitarianism is that present day processes can be used to infer what paleo- environments existed in the past modern ancient Rocks existing at or below the surface tell us what happened in the past 15 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Uniformitarianism Hutton agreed with theories about how sedimentary rocks form, but disagreed with the timescales, and therefore believed the Earth was much older 16 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Uniformitarianism An 18th Century puzzle: If sediments somehow over time solidified into rocks, then 6000 years could not possibly have been enough time for them to form. Image20.gif Charles Lyell (1797 – 1875) rebelled against the prevailing theories of the Earth’s age feeling that they were biased by literal interpretations of Genesis. How long did it take for sediments to be turned into rock? 17 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Observation & Uniformitarianism Lyell went on to study Mount Etna, a volcano on the island of Sicily, where he realized that the 3000 m volcano must have grown from thousands of small eruptions over several millennia. But what really blew his mind was the fossil-rich limestone that clearly ran underneath Etna. Mount Etna must be younger than the limestone!! 18 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 iClicker: Geological Time & Relative Dating Which of these geological units/features is the oldest? A) They all occurred at the same time B) B C) C D) D E) E 19 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Principle of Original Horizontality Due to gravity, sedimentary If sedimentary rocks are rocks are deposited as folded (or faulted), this horizontal layers! occurred after deposition. The Grand Canyon, AZ (USA) 20 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Principle of Superposition In a sequence of bedded rock, the rock layer above is younger than the ones below it. 21 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Cross-Cutting Relationships Igneous intrusions and faults are younger than the rocks that they intrude or break. 22 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  i>Clicker: Geological Time & Relative Dating Which is the correct order these geological units deposited (oldest to youngest)? A) D, C, E, B B) D, B, E, C C) D, B, C, E D) D, C, B, E E) None of the above 23 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Principle of Lateral Continuity Rock units with similar characteristics can be correlated across different exposures over large distances. 24 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Principle of Lateral Continuity This correlation can be aided using fossil assemblages, especially when considering rock exposures separated by 10’s to 100’s of kilometers. 25 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Principle of Lateral Continuity “Western Canada Basin” oil & gas reserves 26 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Unconformities Represent breaks in the geologic record (i.e. erosional surfaces and missing rock in the expected sequence). NOTE: this is another cross- cutting relationship 27 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Hutton’s Unconformity (Scotland) Tilted sedimentary rocks originally deposited in a DESERT 345 million years ago. HOW MUCH TIME DOES THIS UNCONFORMITY REPRESENT? Vertical sedimentary rocks containing marine fossils deposited in a DEEP OCEAN about 425 million years ago. 28 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Unconformities 29 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  iClicker: Relative Dating Which of the following statements is FALSE? A) Unit 8 was deposited after a period of erosion. B) Units 1-5 were originally deposited horizontal. C) Unit 7 was intruded after a period of erosion. D) Units 8-11 have experienced erosion. E) Unit 6 is missing because it was eroded completely away at this location. 30 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Principle of Biotic Succession Organisms have evolved and gone extinct through time. As such, specific groups of fossils succeed one another in the rock record in a definite order (i.e. evolution). Fossil content can therefore be used to help determine the age of the rock units they’re found in. 31 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Geological Time Scale The official geologic timescale… Before Complex Life Complex Life 32 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Geological Time Scale Developed in the 19th century using relative dating techniques (based on fossil assemblages). Eon>Era>Period>Epoch Numeric ages added early 20th century using absolute dating techniques (e.g. radiometric dating). 33 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Geological Time Relative time: age of units relative to one another 1. observed contact relationships between rock units 2. fossil record (by comparing fossils in the unit in question to species of fossils in the evolutionary sequence of fossil forms, i.e., paleontology) Absolute time: specific age of a unit in years Ga: Giga annum (billion years ago) Ma: Mega annum (million years ago) ka: kilo annum (thousand years ago) 34 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 “Millions” and “Billions” How big is a Million or a Billion? One of the hardest things to grasp about geologic time is how LONG a billion years of Earth history actually is. Here are a few comparisons to help understand the concept of a million and a billion: A million sheets of paper would form a tower as high as a 30-storey building. A billion-page stack (1000 million) would be ten times higher than Mount Everest. A million seconds is 21 days. A billion seconds is more than 31 years. 35 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Radiometric/Absolute Dating Parent – an unstable radioactive isotope. Daughter – stable isotope resulting from the decay of a parent. Half-life – time for half of a radioactive nuclei to decay. Radioisotopes (parents) are trapped in minerals when they crystallize and then decay through time. The ratio of parent to daughter isotopes reveals the number of half-lives that have elapsed. Isotopic system Half life Uranium - Lead 4.5 billion yrs Rubidium – Strontium 47 billion yrs Potassium - Argon 1.3 billion yrs Carbon - Nitrogen 5730 yrs 36 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 iClicker: Isotopic Systems Which of the following isotope system would be most appropriate for archaeologists to use when age-dating artifacts? A) Uranium - Lead B) Rubidium - Strontium Isotopic system Half life Uranium - Lead 4.5 billion yrs C) Potassium - Argon Rubidium – Strontium 47 billion yrs Potassium - Argon 1.3 billion yrs D) Carbon - Nitrogen Carbon - Nitrogen 5730 yrs E) All of the above could work well 37 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Radiometric/Absolute Dating Key concept: Ratio of parent to daughter can be used to calculate the age of the mineral/rock 38 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 iClicker: Half-Life The half-life of an isotope system you are using to date an unknown mineral is 2,000 years. If you record that this mineral is 6,000 years old, how much of the daughter isotope exists? A) 12.5% B) 25% C) 50% D) 75% E) 87.5% 39 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Evidence for the Age of the Earth Dates from Meteorites? Dates from the moon? ~4.55 b.y. ~4.5 b.y. 40 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 iClicker: Age of the Earth Can we constrain the age of the Earth by age- dating rocks on Earth? A) Yes, we just need to dig deep enough B) No, since the surface of the Earth is so dynamic, most ancient rocks have been destroyed C) Yes, take a rock in my back yard for instance, it’s probably a few billion years old D) No, rocks on Earth are different to those of other celestial bodies and their age cannot be measured E) Yes just look at the oldest fossils in the rocks and that should give us a good idea about the age of the Earth 41 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Geological Time Scale Radiometric dating indicates that the Earth is 4.6 billion years old. The Precambrian (before macroscopic life) accounts for 87% of geologic time! 42 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Discussion: Geological Time Scale Here’s a puzzle for you: The Hadean is defined as the Eon before the oldest known rocks had formed. If there were no rocks to date, how have geologists determined the age of the Earth? Take a minute to think about this and discuss with your neighbour. 43 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024 Geological Time Scale – Major Divisions Hadean Eon (4.0-4.5 Ga) - Earth’s cooling period - widespread volcanism Archean Eon (2.5-4.0 Ga) - first unicellular life forms, “age of bacteria” - oldest rocks found on the planet - final stages of Earth cooling and formation of the crust 44 of 50 UBC Geological Engineering/EOAS EOSC 210 – Fall2024  Geological Time Scale – Major Divisions Proterozoic Eon (2.5 Ga-545 Ma) - most diamonds formed - oldest sedimentary rocks - formation of ozone layer - first multicellular organisms (jellyfish) Phanerozoic Eon (