Humans originated in Africa about 7 million years ago: if life on earth started 3.5bya ago and represented 24 hours from then to today, how many minutes of these 24 hours would be devoted to this 24-hour clock a) since the first humans showed up?
b) since Humans showed up 300,000 ya?

The double bond between a carbon atom and two oxygen atoms (a molecule of carbon dioxide) has two characteristics. what are they? a.an ionic bond is formed between the oxygen and carbon atoms. b.four valence electrons are shared. c.two valence electrons are shared. d.valence electrons are shared between oxygen atoms.