19.2 The Age of Earth I. The importance of ozone A. Life has existed for 3.5 billion years and 90% of that time life was only in water 1. Sun’s rays would kill land organisms B. As cyanobacteria produced oxygen it floated into upper atmosphere 1. oxygen fused into ozone (O3) 2. this blocks the sun’s UV rays and made land living safe

II. Plants and fungi A. Were the first to invade land 1. 1st problem was how to survive on bare rock a. photosynthetic plants could not get minerals out of bare rock b. fungi could not be photosynthetic but could get minerals 2. Mycorrhizae – association between plants and fungi a. fungi live in the roots of plants 1. plants give fungi food and fungi give plants minerals b. symbiosis – “you help me and I help you” relationship

III. Arthropods A. Have hard outer skeleton and jointed appendages 1. examples – crabs, lobster, spiders, & insects 2. the first arthropods to move on land were scorpions B. Insects have become the most abundant and diverse group of animals ever 1. There are 200 million insects for every human 2. Insects were the first animals to evolve wings a. Allow for a partnership between insects & flowering plants

IV. Vertebrates follow onto land A. Any animal with a backbone 1. First vertebrates were fish, dominated seas for millions of yrs B. Came onto land 350 mya 1. Amphibians were the first a. Ancestors of today’s toad, frog, and salamanders C. Because of strong flexible backbones they could grow larger and soon dominated the landscape