History of Life on Earth

Fig. 25-7

Animals

Colonizationof land

Paleozoic

Meso-

zoic

Humans

Ceno-zoic

Origin of solarsystem andEarth

ProkaryotesProterozoic Archaean

Billions of years ago

1 4

32

Multicellulareukaryotes

Single-celledeukaryotes

Atmosphericoxygen

• Oparin and Haldane hypothesized that the early atmosphere was highly electrical

• Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic(non-living) synthesis of organic molecules in the early atmosphere is possible

• They spent years researching and trying to recreate a closed system that mimic what they believed to be the conditions of early Earth.