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Lecture

16. November 24.docx

2 Pages
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Department
Biology
Course Code
BIO211H5
Professor
Jessica Hawthorn

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Organisms living on islands either become giants or dwarfs. Homo floresiensis got dwarfed because they were isolated on islands. We have the evolution of us: modern humans, derived homo. Neandertalis and us! We both shaer a big brain. We have a giant skull to carry a big brain. We see a relative increase in brain size in the evolution of homo. We have the evolution of a big brain. We’re one of thirteen species. Modern humans are about 250,000 years old. We’ve come up evolved during an interval of global cooling, ice at the south and north pole...as a result of that cooling, there is a series of events that happened – natural cycles of the earth – that result in dramatic changes in climate. We are on earth.we’re spinning around our axis, and orbiting around the sun. The axis is not vertical. We’re tilted at an angle. As we move around the sun, what happens as we begin to move around the sun. At certain points, the southern hemisphere is closer, and at other times, the northern hemisphere is closer. Hence, we have summer and winter. Our orbits are not perfect. We do not have a perfect spherical orbit around the sun. Our axis is not perfect. The axis is not static itself. This variation results in differences in how we receive energy from the sun. When you have a hot house environments, it doesn’t matter tht the amount of energy goes in or out. If you have an ice house environment, you can go from cool to very cold. These periodic changes in the patterns if earth’s orbit around the sun braek into three components. 1. Precession: wobble in axis between northern hemisphere angled toward Sun and Southern hemisphere angled toward Sun. We’re wobbling around our orbit in our axis. We go through a complit wobble every 19 to 23 thousand years. That axis that we’re wobbling around a little bit itself changes. There’s a changing axial tilt. That has a frequency of about every 41 thousand years. 2. Obliquity – (axial-tilt) 3. Orbital eccentricity: we go from being very close to the sun to being very far away from the sun. These all result in changes ni the amount of energy we get from the sun. This is relative change ine energy we get from the Sun. You have a composite pattern of energy change by adding up all three fluctuating cycles. Less enegy means that it’ll be colder. This is teh last major build up of ice on the northern portion of Earth’s hemisphere. Canada i
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