Transcript Document
Lecture 17 Tectonic-scale Climate Change Text book: Ch. 4, p64-67, 71-80, 82-86. • Four Main Processes: – Land-ocean spatial configuration: control where ice sheets form – Spread of sea floor: volcanoes and oxidation of organic carbon in sedimentary rocks, control release of CO2 in the atmosphere – Chemical weathering: control CO2 removal process, a thermostat of the earth’s climate – Uplift-mountain effect: expose fragmented and fresh rock for chemical weathering How does tectonics influence climate? Hundreds of millions of years Plate tectonics and drift concentrated continents at higher latitudes allowed for more ice cover, which reflected more sunlight and created a positive feedback to cause greater cooling. Earth’s climate history: • Early Earth’s history (4.5BY-570MY): – 3.7 BY: May have been 10C warmer – 2.7-1.8BY: widespread glaciers, “snowball earth” – 1.8-1 BY: warm and ice-free, maybe due to catastrophic events, e.g., volcanoes, cometary impact, overturn stagnant ocean – 850-590MY: at least two ice ages 580-0MY: 580-225MY: climate changes was generally colder than the period of 22565MY. 225-65MY: climate was generally warmer with perhaps the warmest during mid-Cretaceous (100MY). 65-0MY: Earth’s climate became colder with time. Why? Snowball earth Mass extinctions of species In-Class Question: Can you link the tectonic movement to the following climate change? 580-225MY: climate changes was generally colder than the period of 225-65MY. 225-65MY: climate was generally warmer with perhaps the warmest during mid-Cretaceous (100MY). 65-0MY: Earth’s climate became colder with time. warmest coldest Tectonic-scale Carbon Dioxide Fluctuations (p. 71-75) Seafloor spreading leads to increased periods of volcanic degassing of CO2, which causes warming. Higher temperatures leads to increased weathering, which will remove CO2 from the atmosphere and reverse warming in a negative feedback loop. Earth’s Climate History in the Last 550 Myr 1. 2. 3. Over the past 550 Myr, three Icehouse periods (430, 325-240, 35-0 Myr ago). For most of the last 550 Myr or the earth’s entire history, the climate was much warmer than today. Tectonic-scale climate change is caused by plate tectonics Land/ocean positions and sizes Ocean floor spreading/CO2 increase Mountain building (uplift) & weathering / CO2 decrease 4. Part II p. 82-83; Ch. 4, 5, 6, 7 Other causes. Chemical weathering (chemical breakdown of minerals or rocks)-a thermostat of earth’s climate (Ch. 4, p75-80) Carbonic acid Examples: (Calcite) (calcium ions) Limestone + carbon dioxide + water dissolved ions + bicarbonate CaCO3 + CO2 + H2O Ca2+ + 2HCO3- Cretaceous Greenhouse Earth Warm period of dinosaurs Evidence No record of glaciers or polar ice caps Faunal/floral zone latitudinal shift Isotopes warmer oceans Environments shift with near tropics to the poles Oceans/Atmosphere/Land Features Sea level 100-200 m higher because of no polar ice caps Intense storms (hurricanes) because of warmer waters Stronger hydrologic cycle Less wind because lower T and P gradients globally More plants, more flowers; extent of dry land reduced by flooding Causes Sun-Earth relationship Land-sea configuration More oceans in low latitudeslower albedo More land in high latitudesmore plants More CO2 in atmosphere (4-8 x) The World 100 Myr Ago (p. 82-85) Flooding of The Continents 1. The last time atmospheric CO2 concentrations and temperatures were much higher than today was in the age of dinosaurs. 2. Agriculture revolution began 10,000 years ago. 3. Human population explosion in the past 100 years. Today: 6 billion 6 5 million years 10 million PRESENT 55 million years years 3.5 Million years 18,000 years 1 Million years 10,000 years 230,000 years 1,000 years 100,000 years What about Texas? Sea levels were much higher than today, and Texas was mostly under water Climate change was one important reason that the dinosaurs disappeared. Global Cooling Trend in the Last 55 Myr Ch. 7 Causes: decrease in ocean floor spreading rate; uplift weathering; ocean heat transport through gateways; ice-albedo feedbacks Cooling from leaf outline Cooling from ocean isotopes Decrease in spreading rate Summary: • Four Main Processes control the link between tectonic movement and climate: – Land-ocean spatial configuration: control where ice sheets form – Spread of sea floor: volcanoes and oxidation of organic carbon in sedimentary rocks, control release of CO2 in the atmosphere – Chemical weathering: control CO2 removal process, a thermostat of the earth’s climate – Uplift-mountain effect: expose fragmented and fresh rock for chemical weathering