The Origin and Early Evolution of Life Lecture

The Origin and Early Evolution of Life Lecture 19

The Big Bang § 12 -15 (13. 8) billion years ago all matter was compressed into a space the size of? § Our Galaxy § Our Solar System § Our Plant § Our Atom § Sudden instantaneous distribution of matter and energy throughout the known universe

Timeline § § § § § 4. 6 to 3. 8 billion years ago - Leads to solid crust 3. 8 Water forms 2. 8 to 3. 2 - Life starts as prokaryotic cells 1. 5 Eukaryotic cells develop 545 Cambrian explosion 500 Fish 350 Amphibians 300 Reptiles 1. 6 humans

Timeline: Archaean Eon and Earlier § 4, 600 mya: Origin of Earth § 4, 600 - 3, 800 mya (about 800 million years) § Formation of Earth’s crust, atmosphere… § Formation of the Moon § Chemical and molecular evolution only § Then came the First cells (anaerobic bacteria)

Earth Forms § About 4. 6 billion years ago § Gas, Minerals and ice orbiting the sun started clumping together § Heavy metals moved to Earth’s interior, lighter ones floated to surface § Iron core § Produced outer crust and inner mantle

First Atmosphere § Hydrogen gas § Nitrogen § Carbon monoxide § Carbon dioxide § No gaseous oxygen

Earth Is “Just Right” for Life § IF…Earth was; § Smaller in diameter, gravity would not be great enough to hold onto atmosphere § Closer to sun, water would have evaporated § Farther from sun, water would have been locked up as ice

Stanley Miller’s Experiment § Mixed methane, hydrogen, ammonia, and water § Simulated lightning § Amino acids and other small molecules formed Animation

How Did Cells Originate? § In the first 600 million years or so of Earth history, enzymes, ATP, and other crucial organic compounds probably assembled spontaneously - nothing came of it! § Then, by a still disputed mechanism, the concoction came together randomly to make some primitive organic molecule…

Possible Sequence

RNA World § DNA is genetic material now § DNA-to-RNA-to-protein system is complex! § RNA may have been first genetic material § RNA can assemble spontaneously § How switch from RNA to DNA might have occurred is not known

The First Cells § Originated in Archaean Eon § There were prokaryotic cells § These were heterotrophs § Secured energy through anaerobic pathways § No oxygen present, therefore they must have § Relied on glycolysis and fermentation only!

Proterozoic Eon § FIRST § Origin of photosynthetic eubacteria, as a result… § SECOND § Then, Oxygen accumulates in atmosphere, and § THIRD § Origin of aerobic respiration

Advantages of Organelles § Nuclear envelope may have helped to protect genes from competition with foreign DNA § ER channels may have similarly protected vital proteins §…

Possible Origin of ER

Theory of Endosymbiosis § Lynn Margulis § Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms § Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts § http: //www. sumanasinc. com/webcontent/anis amples/nonmajorsbiology/organelles. html

Evolutionary Tree

Evolutionary Tree