History of Life on Earth Theories and Ideas on How Life Began and What Has Happened Since

From Nothing to Everything? When the earth formed some 4.6 billion years ago, it was a lifeless, inhospitable place. A billion years later it was teeming with organisms resembling blue-green algae. How did they get there? How, in short, did life begin?

The Big Bang: Earth’s Prehistory

The Big Bang: Earth’s Prehistory The Big Bang Theory is the dominant scientific theory about the origin of the universe. Created the universe between 10 billion and 20 billion years ago Cosmic explosion hurled matter in all directions Period of rapid heating and rapid cooling occured

The Prebiotic Earth: First Billion Years

The Prebiotic Earth: First Billion Years In order for life to exist on Earth, four requirements must have existed: Presence of chemical building blocks Source of energy Little or no free oxygen Time Major elements found in living things: C, H, O, N, P, S

Oparin’s Hypothesis

Oparin’s Hypothesis 1930s - Alexander Oparin hypothesized that life began between 3.9 to 3.5 billion years ago. Simple organic molecules containing carbon formed Energy from the sun, lightning, and earth's heat triggered chemical reactions Organized by chance into complex organic molecules 1952 - Miller-Urey Experiment Simulated conditions on Earth ~4 billion years ago Experiment made some of the fundamental building blocks of life This suggests that these can form naturally Still flaws with the experiment though Examples: Amino acids, fatty acids, urea; The “Primordial Soup”: early oceans probably filled with rich mixture of organic compounds

Iron-World Hypothesis

Iron-World Hypothesis Suggests that life began in deep-cracks in the Earth’s deep ocean floor Lab experiments show production of simple organic compounds Hot water, carbon monoxide and minerals are found in hydrothermal vents

Evolution of Oxygen Content of Earth’s Atmosphere

The Origin of Life on Earth

The Origin of Life on Earth Life began in the sea as single-celled organisms Life develops into more complex forms through gradual evolution Early organisms had no hard parts to leave fossil Gradual evolution spans thousands of generations; earliest, microscopic fossils are about 4 billion years old

Geological Time Scale

Catastrophes? That’s Normal!

Catastrophes? That’s Normal! Life on Earth has been punctuated by catastrophes Catastrophes cause ecosystems to collapse and species become extinct Adaptive radiation occurs following mass extinction Adaptive Radiation: the evolution of new species over millions of years

Endosymbiosis Theory

Endosymbiosis Theory Theory suggests that prokaryotes (simple cells) gave rise to the first eukaryotes (more complex cells) Bigger prokaryotic cell engulfed smaller heterotrophic prokaryotic cell Prokaryotic cell became dependent on host cell, which received more ATP production Mitochondria have their own DNA, RNA, and ribosomes; Amoebas lack mitochondria and require a symbiotic relationship with an aerobic bacterium.