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Earth 2
Lecture 15
| Question | Answer |
|---|---|
| Science knowledge | is a social construction |
| Science and social construction | Scientists are a social group. Experts in the field help determine what does and does not get published or funded. Political, social, economic forces influence the trajectory of scientific advancement |
| Scientific theories are | explanations, nests, or systems of explanations. No one test can determine the veracity of a theory. Falsification is not a tenable strategy |
| Geology is a | historical science and hermeneutic (interpretive) |
| Geologists: | look for and interpret signs from past processes, construct a story based on the signs, CANNOT run an experiment to test the story, employ three different research strategies |
| Research strategy 1 | improving-to increase the problem-solving effectiveness and solutions of the theory, removing difficulties |
| Research strategy 2 | Attacking-to raise the difficulties in answering the data of competing solutions or theories |
| Research strategy 3 | Comparing-where problem-solving effectiveness is shown to be better than the competing theory |
| The time of the asteroids: Hadean Era (4.54-4.0 BYA): what we observe | The scars (craters) on the moon and Earth. Collisions converted to heat. Modern volcanoes, examining meteorites |
| The time of the asteroids: Hadean Era (4.54-4.0 BYA): what we interpret | Violent beginnings, Molten, sterile earth. Volcanoes and outgassing of CO, CO2, NH4, HCN, H2SO4,H2O. Rampant greenhouse effect. Phosphides and carbon compounds arrive on meteorites |
| Hadean Era (4.54-2.0 BYA) | Origin of solar system (NOT THE BIG BANG), from explosion of super nova. Debris from explosion begins to coalesce into larger masses that eventually become planets. Planets begin to "clean up" debris. Impacts of debris->EK into heat energy |
| The Moon (4.53 BYA) | The moon is far bigger relative to the Earth than other moons to their planets in the solar system. Fission hypothesis, Capture hypothesis, impact hypothesis |
| Fission Hypothesis | spinning earth jettisoned part of itself into orbit-the moon |
| Capture hypothesis | Huge wayward satellite captured by the earth's gravitational field-the moon |
| Impact hypothesis | A large asteroid collided with earth and the debris coalesced and began orbiting the earth-the moon |
| Steno's principle of superposition | Layers of sedimentary rock recorded the passage of time from older (deeper) to younger (shallower) |
| Dinosaur observations | Dinosaur fossils were quite abundant in deeper layers, but they seemed to abruptly disappear at the same level (same time) |
| Georges Cuvier | anatomist. Worked on fossils of animals that would be classified as mammals, but no longer existed on Earth. The lower the fossils the less they looked like modern day organisms. The change in life forms could be very abrupt due to catastrophic event |
| Georges Cuvier postulated | the notion of mass extinctions: catastrophism. Did not believe in Darwinian evolution |
| Charles Lyell | Famous early geologist. There can be no catastrophic events, only slow change over long periods of time. Uniformitarianism. Supported Darwinian evolution |
| Charles Lyell described Cuvier's mass extinction | Cuvier's mass extinctions are merely the result of a lack of sedimentation in areas, so you don't see what was really a slow decline |
| A simply controversy in the early days | The side you agreed with did not depend on the evidence, because everyone was looking at the same data. It was sensitivity to one paradigm or the other that influenced the interpretation |
| Mostly, established science agreed that | the extinction was gradual (uniformitarianism) |
| Published science on dinosaur extinction part one | high levels or low of CO2, ocean or volcanism, cataract blindness, climate too cold, wet or dry, Super nova explosion, caterpillars, multi-layer eggshells, entropy, |
| Published science on dinosaur extinction part two | disease, increased metabolism, poison from fungi, loss of habitats, parasites, overpopulation, decrease in sexual activity, slipped vertebral disks, sunspots |
| Walter Alvarez | him and his team were investigating foraminifera extinction across the K-Pg boundary. Not concerned about dinosaur extinction. Found a clay layer at the transition point. Wanted to know the length of time to deposit the clay |
| Walter and his father | his father was a chemist. Father suggested testing for iridium in the clay which is constantly settling in dust in the air. Iridium not abundant at earth's surface but in meteorites. If Iridium is low, it was deposited quickly. If high, it took long |
| What is high Iridium in clay | Normal (0.1ppb), high is (3-160ppb) |
| How can we get high Iridium | Supernova explosion, when stars explode, they create lots of heavy elements. A nearby supernova explosion would shower the earth with that and other heavy elements, extreme volcanic events. It exists at high [] deep in the earth, asteroids |
| Abductive reasoning: eliminating possibilities | Research strategy 3: finding evidence for one cause over the other two |
| Back to the field...new discoveries for dinosaurs | High levels of Iridium, Plutonium 244, shocked quartz, large amounts of sulfur, massive climate shift, increase in atmospheric CO2, massive reduction in photosynthesis, massive lava flows, glass spherules |
| Alan Hildebrand | sympathetic to impact hypothesis. Went looking for ejecta deposits of the correct age. Thicker deposits are closer to impact, such deposits reported from DSDP, basaltic (ocean crust) composition, off east coast of N America |
| Our Own Dr. Hildebrand | Found what he described as ejecta deposits in and around the gulf of Mexico and US. Using thickness measurements found general location of impact in southern Gulf. Located map with gravity anomaly showing crater. Dated sediments |
| What it must have been like when the dinos died | Firestorms, giant tsunamis, seismic shockwaves |
| What is must have been like: Firestorms | The impact ejected material that fell back to Earth, heating the atmosphere and igniting continent-scale wildfires |
| What is must have been like: Giant tsunamis | The impact generated enormous tsunamis, which caused rapid burial of organisms under thick layers of sediment and debris |
| What is must have been like: Seismic shockwaves | The impact was so powerful it triggered massive earthquakes and seismic waves that caused seiches (standing waves) in bodies of water around the world |
| Schulte et al. 2010 | Though it was being taught as the consensus since the 1990s the impact theory for dinosaur extinction officially became the consensus view with the publishing of this paper in Science |
| Keller, 2011-(RS 2) attacking research strategy, raising difficulties, mass extinction | other impact craters found of similar magnitude are not associated with mass extinction. |
| Keller, 2011-(RS 2) attacking research strategy, raising difficulties | What are considered rapidly deposited tsunami layers have signs of burrow and benthic (floating) foraminifera, meaning longer period of deposition. age dates older than K-Pg boundary date |
| Keller, 2011-(RS 1) improving own explanation research strategy | Geochronology, paleomagnetism, stratigraphic studies pinpoint Deccan Traps eruptions (end of main phase) at the K-Pg extinction event. The amount of S and Cl based gases released by such eruptions calculated, would have caused environmental catastrophe |
| Petersen 2016 | Combined effects-two pulses of extinction. Warming associated with volcanism and again with the impact and volcanism. Impossible to separate causality between the two. Often, consensus view is made from parts of each side of the controversy |
| Peterson Sampled shells in Antarctica. | Continuous sedimentation. Shells well preserved to give temperature data |
| The day the dinos died 2019 | Montana outcrop that is a tsunami deposit supposedly from the impact. No one has found fossils at the K-Pg boundary before. Hasn't shared anything more than the images of fossils. Doesn't discount volcanism |
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