Origin of Life on Earth!

1. Origin of Life on Earth!

2. If life evolves, where did the first life come from? • The big bang • 15 billion years ago the universe was a superdense mass that exploded • Matter hurled into space, formed galaxies and stars • Gravity pulled in some matter to orbit stars and became planets • Earth is likely 4.6 billion years old

3. Geologic Timescale

4. Early Earth • Early conditions on earth unique • As Earth cooled, escaping gas formed primitive atmopshere: N2, CO2, H2O vapor, H2, CO • Atmosphere contained little oxygen gas (O2) • Surface of the planet was shallow seas, with lots of violent storms and volcanic eruptions • With no oxygen, lots of energy, and shallow seas early molecules may have formed spontaneously.

5. Origin of life hypotheses • Three hypotheses, but we will focus on one that is actually testable • Life evolved from nonliving substances through interaction with the environment

6. Chemical Evolution • Energy sources (radioactivity, lightning, cosmic radiation, and heat) caused gases in atmosphere to react forming organic compounds • Heterotroph hypothesis in three steps • Had to be a supply of organic molecules (monomers) produced abiotically • Monomer assembled into polymers due to the high free energy of early Earth • Other processes organize polymers into a system that could replicate itself using monomers that were produced initially • Why heterotoph? Lots of organic molecules to eat, so little competition and no advantage for an autotroph

7. Evidence of early organic monomer development • Miller and Urey produced amino acids in this experimental set up circa 1950 • Recent experiments have created 13 of the 20 amino acids, DNA and RNA bases small amounts of ribose sugar • But some of these molecules have been found in meteorites

8. Formation of Polymers • Need concentrated monomers to make a polymer • Clay particles attract charges regions of the monomers and may have held them in place for polymerization reactions

9. Polymer Self Replication (RNA World Hypothesis) • RNA is a single stand nucleic acid that folds dues to base paring • 3-D structure can work like an enzyme to catalyze reactions • RNA also stores information • RNA could store information on how to build proteins and catalyze production • Resulting proteins may have promote more RNA polymerization and copying

10. WAS THIS LIFE? • Life is a self sustaining chemical system capable of undergoing Darwinian evolution which contains • Self reproduction • Mutation that can be inherited • Natural selection • Life on earth also contains cells • Unsure how first cell evolved, but many hypothesis on development of first cell membrane • Protobionts will form under some conditions and have some characteristics of life

11. Fossil Prokaryote • Fossil of ancient bacteria • 3.5 BILLION Years old • Found in Australia

12. Formation of Eukaryotes • Endosymbiotic theory: Eukaryotes developed from a symbiotic relationship between two prokaryotes • Mitochondria and Chloroplasts were likely once free living prokaryotes • Both have their own DNA and ribosome similar to prokaryote structure • Both replicate independently of cell division • Both have double membranes