TIMES

------------+------------------------+---------------------------
| MILLIONS OF YEARS AGO | STAGES OF ANIMAL
ERAS | (VERY UNCERTAIN) | DEVELOPMENT
------------+------------------------+---------------------------
| | Age of Man
Recent Life | | (Quaternary)
(Cenozoic) | 0 to 5 | Age of Mammals
| | (Tertiary)
------------+------------------------+---------------------------
Middle Life | |
(Mesozoic) | 5 to 10 | Age of Reptiles
------------+------------------------+---------------------------
| | Age of Amphibians
| | (Carboniferous)
Ancient Life| | Age of Fishes
(Palaeozoic)| 10 to 25 | (Devonian)
| | Age of Invertebrates
| | (Silurian and Cambrian)
------------+------------------------+---------------------------
Dawn Life | | Earliest Animals and
(Eozoic) | 25 to 50 | Plants
------------+------------------------+---------------------------

Having seen what the scientist supposes to be the method of formation
of the earth itself, it will be interesting next to consider what the
biologist surmises as to the origin of the life upon the earth. Here
again two explanations hold. The one, and distinctly the older of the
two, says that at some time in the far distant past, under conditions
which are rarely if ever duplicated, out of the lifeless material of
the globe were produced simple and low forms of life. These could not
properly be called either animal or plant, but partook somewhat of the
nature of both. Of this there is at present no evidence whatever. The
only reason we have for suggesting it is that, if we understand the
past conditions on the earth, there was a time when life was
impossible. Now we find life. Hence it must have arisen. This of
itself, of course, furnishes no proof, but leads us to try to imagine
how the transition might have come about. Every scientist who believes
in this form of origin holds that if the exact conditions are repeated
the result will occur once more. He may believe that