Lesson 1 – The changing Earth

1. P1 – the earth and the universe Lesson 1 – The changing Earth

2. There are some really dull things in the solar system, for example, asteroids don't do much except rotate around the sun and they can also be very dangerous etc if one was to come crashing to earth that would be the end of life full stop. However earth is different it possesses something that all the other planets and things in our solar system do not and that would be oxygen and life.

3. The Earth is an active planet • Its kind of tempting to think that the earth is a steady, unchanging place that will always look as pretty much as it does now. • But no... In a few tens of millions of years, Earth is going to look alot different • Mountings that are enormous today wont be nearly so grand, and the map of the world will be very different – whole continents would have moved • This is nothing new – earths been changing for thousands of millions of years

4. Rocks show changes in the earth Rocks change over the years – so the surface of the earth hasn’t always looked the way it does now. • Look at the grand canyon, for example. Over time, the Colorado river has eroded the rock, leaving and impressive slash through the middle of Arizona . • Erosion goes on everywhere. We see it happening, for example, when the cliffs are worn away from the sea. But other processes must be happening as well. If not, all the high ground would have been worn down by now... Earth would be perfectly smooth. • So some process must be making new mountains. And evidence is pretty easy to find – E.g when lava from volcanoes set it forms brand new rock. • There are also some spectacular forces at work in the earth, which can push up old rock to make new mountains – some rock formations show rock that has been squeezed so hard its just folded.

5. More evidence that rock is forming comes from fossils. The animals and plants couldn't have dug themselves into the middle of rocks – the rocks must of formed around them. This type of rock is made by sedimentation – particles eroded from existing rock get washed to the sea and settle as sediment. Over time, these sediments get crushed together to make new rock. All the rock processes that we can see happening now – E.g erosion, sedimentation, volcanic activity, etc. Will have been going on for millions of years. Geologists can use that fact to explain how various modern landscapes were formed

6. Scientists can use radioactivity to tell how old rocks are • By looking at the proportions of radioactive potassium-40, and the element it decays into, in certain rocks, scientists can get a good idea of when the rocks were formed. (its tricky but it can be done) • Scientists can use this to help estimate the age of the planet – the earth must have been around at least as long as the oldest rocks.

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