End Show Slide 1 of 36 Copyright Pearson Prentice Hall 17-2 Earth's Early History

End Show Slide 2 of 36 Earth is the only known planet known to support life! Conditions Necessary for Life: 1.Liquid water 2.A moderate temperature 3.Free oxygen in atmosphere 4.Sunlight 5.Absence of toxic substances in atmosphere 6.Absence of lethal radiation Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 3 of 36 Copyright Pearson Prentice Hall Formation of Earth Earth is made mostly of rock! High temps on Earth caused most rock to melt and separate. Dense materials (iron and nickel) sank and formed the core. Lighter materials settled above the core forming the mantle and crust.

End Show 17-2 Earth's Early History Slide 4 of 36 The active volcanoes on Earth released water vapor which built up in the atmosphere. The water vapor condensed and fell back to Earth as rain. Over millions of years, the liquid water collected in depressions on Earth’s rocky surface and formed oceans. Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 5 of 36 Copyright Pearson Prentice Hall In addition to water vapor, the erupting volcanoes released other gases forming Earth’s early atmosphere (gases that surround Earth). Formation of Earth

End Show 17-2 Earth's Early History Slide 6 of 36 Copyright Pearson Prentice Hall Formation of Earth These gases were methane, hydrogen, nitrogen, ammonia, carbon dioxide, and carbon monoxide.

End Show 17-2 Earth's Early History Slide 7 of 36 Today’s atmosphere contains free oxygen (oxygen gas that is not combined with other elements) and a layer of ozone that protects living things from harmful radiation. Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 8 of 36 Copyright Pearson Prentice Hall The First Organic Molecules The Beginning of Life on Earth The lack of free oxygen in Earth’s early atmosphere would have prevented the survival of most modern organisms so….. In the 1950s, Stanley Miller and Harold Urey tried to model early Earth Conditions.

End Show 17-2 Earth's Early History Slide 9 of 36 Copyright Pearson Prentice Hall The First Organic Molecules Miller and Urey's experiments suggested how mixtures of organic compounds needed for life could have formed from simpler compounds present on an early Earth. Their experiment showed that amino acids could form from matter present on early Earth.

End Show 17-2 Earth's Early History Slide 10 of 36 Copyright Pearson Prentice Hall The First Organic Molecules Miller and Urey’s Experiment Mixture of gases simulating atmosphere of early Earth Condensation chamber Spark simulating lightning storms Water vapor Liquid containing amino acids and other organic compounds Cold water cools chamber, causing droplets to form.

End Show 17-2 Earth's Early History Slide 11 of 36 Copyright Pearson Prentice Hall Free Oxygen Primitive Organisms and the Endosymbiotic Theory Fossil evidence indicates that the first organisms appeared in Earth’s oceans about 3.5 billion years ago These organisms formed without Oxygen They were prokaryotes!

End Show 17-2 Earth's Early History Slide 12 of 36 Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 13 of 36 Fossils showed that cyanobacteria (prokaryotes that make food by photosynthesis) became common in shallow areas of Earth’s oceans about 3 billion years ago. Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 14 of 36 Photosynthesis by cyanobacteria gradually increased the amount of oxygen in the atmosphere creating free oxygen. This free oxygen bred life to more complex, oxygen breathing life forms! Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 15 of 36 Copyright Pearson Prentice Hall Origin of Eukaryotic Cells What hypothesis explains the origin of eukaryotic cells?

End Show 17-2 Earth's Early History Slide 16 of 36 Copyright Pearson Prentice Hall Origin of Eukaryotic Cells The Endosymbiotic Theory The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms.

End Show 17-2 Earth's Early History Slide 17 of 36 Copyright Pearson Prentice Hall Origin of Eukaryotic Cells Endosymbiotic Theory Mitochondrion Aerobic bacteria Nuclear envelope evolving Ancient Prokaryotes Plants and plantlike protists Primitive Photosynthetic Eukaryote Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote Chloroplast Animals, fungi, and non-plantlike protists Photosynthetic bacteria

End Show 17-2 Earth's Early History Slide 18 of 36 Early Eukaryotes The first eukaryotes evolved around 2 billion years ago. Included algae. Photosynthesis by algae added more oxygen to the atmosphere. Sexual reproduction evolved around 1.2 billion years ago Life became much more varied and complex about 540 million years ago. This event is known as the Cambrian Explosion! Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 19 of 36 All the major animal groups first appeared during the Cambrian Period. Fossil evidence shows plant life started around 480 million years ago. Land plants are the major source of atmospheric oxygen today. Copyright Pearson Prentice Hall

End Show 17-2 Earth's Early History Slide 20 of 36 Copyright Pearson Prentice Hall Order of life on Earth Anaerobic Prokaryotes Photosynthetic Prokaryotes Unicellular Eukaryotes Multicellular Eukaryotes