Geologists, paleontologists and archaeologists have pieced together a fairly detailed account of how Earth and its inhabitants evolved.
But just how do researchers determine the ages of the materials they unearth?
By comparing how much carbon-14 there is in the dead organism with the amount in a living one, the age of the dead organism can be estimated.
The half-life of uranium-238 is 4500 million years.
Which would make the age of the earth in this case 4 billion years instead of 4.55 billion.
Or is it the same as with C is formed in the higher atmosphere through interaction of cosmic rays with nitrogen atoms.
These planetoids collided together and eventually enough came together to become Earth-sized.
And last week scientists announced that new dates for an extinction event that claimed most of Australia's large animals show that humans, not the climate, wiped them out.