Geological Timescale 

The Earth is about 4,600 million years old. To get an idea of how long a period this is, imagine that the Earth was created at midnight and that it is now noon -12 hours later. On this scale:

• The first rocks formed from the molten Earth at 2.52 a.m.
• Bacteria and algae appeared at about 4.20 a.m.
• Many invertebrate life-forms appeared at about 10.30 a.m.
• The "age of dinosaurs" was from about  11.25 a.m. to 11.50 a.m.
• The first hominids appeared at about 30 seconds to noon.
• "Civilization" commenced at one tenth of a second to midnight.