Geology Reference
In-Depth Information
Right Here, Right Now: The Reign of
Homo Sapiens
The Cenozoic era has not ended. Many geologists consider right now to be part of the
Quaternary period that began about 2.8 million years ago. Other scientists have pro-
posed that a new period has begun: the
Anthropocene
, the geologic period of humans.
Biological classification groups humans, or
Homo sapiens,
with primates, including mon-
keys, lemurs, and apes. Within the primates, humans are more closely related to gorillas
and chimpanzees, but they stand alone as hominids.
The evolutionary story of hominids began nearly 7 million years ago at the end of the
Miocene epoch when hominids and chimpanzees diverged from a common ancestor.
Fossils indicate that by 4 million years ago, australopithecines appeared, mostly in
Africa. Australopithecines included five different species of hominids that were similar
to modern humans in that they were
bipedal
(walking upright on two legs), but they still
had many ape-like and primitive primate features. A few species of australopithecines
were living side by side with the early ancestors of modern humans,
Homo habilis
and
Homo erectus,
around 2.8 million years ago.
The direct path from
Homo erectus
and
Homo habilis
to modern humans
(Homo sapiens)
is not precisely documented. Scientists have proposed and continue to test two promin-
ent hypotheses:
Out of Africa:
The “out of Africa” hypothesis suggests that early humans evolved
from a single mother who lived in Africa and whose offspring migrated out of
Africa around 100,000 years ago into Europe and Asia.
Multiregional:
The multiregional hypothesis proposes that multiple populations of
early humans were scattered across Europe and Asia. Occasional contact and in-
terbreeding led to the characteristics of modern humans among populations far
enough separated to result in the wide diversity of features we see today.
Seeking answers to mysteries of the past
Just thinking about pollen makes some people sneeze. But pollen grains are a very useful tool to scient-
ists asking questions about the past. Pollen grains are made of a special organic protein called
sporo-
pollenin
that can last for millions of years if preserved under the right conditions. And pollen grains are
tiny (microscopic) and abundant (millions of them fit on the tip of your pinky finger). Pollen grains come
from flowering plants, and those plants need certain conditions of temperature, sunlight, water, and
