Transcript: Hello, everyone. My name is Anthony, and I am here today to talk about the causes of the Ice Ages. So before we begin, what is an ice age? For beginners, an ice age is a prolonged interval of time that can range from millions to tens of millions of years where global temperatures are relatively cold and large areas of our planet is being covered by continental ice sheets and alpine glaciers. Throughout history, it’s suspected that extended periods of glaciation are in fact moving in a cycle, and there have been several instances in the Earth’s long history where the majority of the planet is covered with ice. Records show that cold times tend to develop slowly, but end abruptly. At least 5 ice ages have occurred in our Earth’s history, and another name you may hear that is synonymous to our Ice Age period is the Pleistocene epoch, which began about 2 to 3 million years ago. A main characteristic of the Pleistocene epoch is the significant number of advances and retreats of glacial ice. The times during the glacial ice retreat is known as the interglacial periods. Today, we are going to learn about what scientists believe is the cause of these Ice Ages. Before we can begin, we must consider the two basic questions geologists face in an attempt to explain the causes of these glacial ages. What caused the onset of glacial conditions? What caused the alternation of glacial and interglacial stages that have been documented for the Pleistocene epoch? The first hypotheses scientists have for a cause of an ice age has to do with plate tectonics. The positioning of continental plates is a huge factor in the development of an ice age. Land masses being at high latitudes is a requirement for a huge ice mass to form. Keep in mind that ice sheets cannot form over oceans. When the Pleistocene epoch began around three million years ago, the Antarctica and much of North America and Eurasia continents resided in the high latitudes, and this configuration led to massive glaciation on these continents. Considering how slow continental plates move annually, the huge changes made in the millions of years can explain the climate change on our planet. However, this hypothesis fails to explain why the short term changes during the interglacial periods occurred. Another hypotheses scientists have for a cause of the ice ages is changes in the Earth’s orbit. It’s important to understand that there are many factors that contribute to the amount of solar radiation the Earth receives. These factors include the eccentricity of the orbit around the sun, the tilt of the Earth's axis (obliquity) , and the direction the north pole points (precession). The variation and distribution of solar radiation caused by these factors could very well change the global climate and cause glaciation. This hypothesis successfully answers the question that discusses about the interglacial times. There are also smaller hypotheses developed by scientists. One of the more significant one has to do with the chemical composition of the Earth. The amount of CO2 in the atmosphere determines the global climate, and this may have also led to glaciation. However, other scientists are skeptical that the magnitude of past CO2 changes were big enough to cause an Ice Age. Much of the information known today about the Ice Ages is recovered from studying ice cores, deep sea sediments, fossils, and landforms. All in all, although scientists are not 100% sure about how glaciation happened, it’s generally accepted that the movement of plate tectonics and changes in Earth’s orbit are the two main factors. Comments: -The five most recent ice ages are the ones that we know most about today, since there are landforms, ice cores, etc. to study off of. -However, over the course of Earth’s long history, there has been a lot more number of ice ages. -The difference between temperatures of an Ice Age and not an Ice Age is not significantly huge. It’s generally between five to seven degrees cooler during an ice age. -During the Ice Ages, only the continents of high latitudes were glaciated. The rest of the planet was not frozen. -Actually, ice sheets can form on oceans, but they are not called continental ice sheets, but instead is known as polar ice. -The movement of plate tectonics also affected how the heat waves circulated the Earth as the ocean currents changed paths. This can very well be enough to start an ice age. References for Information: http://geology.utah.gov/map-pub/survey-notes/glad-you-asked/ice-ages-what-are-they-and-what-causes-them/ Earth, An Introduction to Physical Geology. (Lutgens, Tarbuck, Tasa Tenth Edition) Chapter 18, p. 512-515 References for Pictures and Figures: https://docs.google.com/document/d/1z_UAZJx--vvmnx-YGYXclW1KKQseeH3OxGC-RbnPKd8/edit?usp=sharing

• published: 10 Apr 2015
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