Slide 1

History of Life on Earth

Theories and Ideas on How Life Began and What Has Happened Since

Slide 2

From Nothing to Everything?

Slide 3

The Big Bang: Earth’s Prehistory

Slide 4

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

Slide 5

The Prebiotic Earth: First Billion Years

Slide 6

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

Slide 7

Oparin’s Hypothesis

Slide 8

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

Slide 9

Iron-World Hypothesis

Slide 10

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

Slide 11

Evolution of Oxygen Content of Earth’s Atmosphere

Slide 12

The Origin of Life on Earth

Slide 13

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

Slide 14

Geological Time Scale

Slide 15

Catastrophes? That’s Normal!

Slide 16

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

Slide 17

Endosymbiosis Theory

Slide 18

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