Environmental Engineering Reference
In-Depth Information
Modern humans
(Homo sapiens sapiens)
appear about
2 seconds
before midnight
Recorded human
history begins
1
/
4
second
before midnight
r
s
Age of
mammals
Origin of life
(3.6-3.8 billion
years ago)
Age of
reptiles
midnight
12
Insects and
amphibians
invade
the land
9
3
AM
6
6
PM
First fossil
record of
animals
3
9
Plants begin
invading
land
12
noon
Evolution and
expansion of life
Figure 4-3
Natural capital:
greatly simplified overview of the biological evolution of life on the earth, which
was preceded by about 1 billion years of chemical evolution. Microorganisms (mostly bacteria) that lived in
water dominated the early span of biological evolution on the earth, between about 3.7 billion and 1 billion
years ago. Plants and animals evolved first in the seas. Fossil and recent DNA evidence suggests that plants
began invading the land some 780 million years ago, and animals began living on land about 370 million years
ago. Humans arrived on the scene only a very short time ago. We have been around for less than an eye blink
of the earth's roughly 3.7-billion-year history of biological evolution. Although we are newcomers, humans have
taken over much of the planet and now have the power to cause the premature extinction of many of the other
species that travel with us as passengers on the earth as it hurtles through space.
