Big History: A Summary of Evolution of Life on Earth

The first organisms, simple photosynthetic bacteria, appear in sediments about 3.5 billion years old, only about a billion years after the planet was formed. These single cells were all that occupied the Earth for the next two billion years, after which we see the first simple “eukaryotes”: organisms having true cells with nuclei and chromosomes. Then, around 600 million years ago, a whole gamut of relatively simple but multicelled organisms arise, including worms, jellyfish, and sponges....

 Weening Among Human Ancestors

Archaeologists have discovered that since the Pleistocene, humans lave always suckled infants for several years. Using biochemical analysis given human population when its children moved from breast milk to other foods. In one group of skeletons from South Dakota dated between 5500-2000 b.c., children were apparently depending on food other than mother's milk by the time they were twenty months of age.^' Recorded history also tells a similar story. Middle Eastern groups in 3000 B.C. were brea...