The Cambrian Period
• Occurred 550-490 million years ago.
• Was the first period of the Paleozoic era.
• Adam Sedgwick named the period after
the Roman name for Wales, Cambria. It
was named for the site, in which shale and
sandstone make up a two mile thick layer
Origin of the period
• Generally, the beginning of the Cambrian
period is said to be marked by the
appearance of the fossil Trichophycus
Some argue that the appearance of trilobites marks the
beginning of the Cambrian period.
To the left we
see a map of
In the diagram to
the right, we see
position of the
• This period is characterized by a huge burst of life in the
form of great animal diversification, known as the
Cambrian Explosion where in that time annelids,
arthropods, mollusks, and many other phyla of animals
appeared for the first time. Direct descendants of these
animals are still present today, such as the jellyfish:
• Mostly consisted of desert and badlands,
however, some green algae was thought to
• No land plants.
Climate of the Cambrian Era
• Warm, wet, and mild weather.
• No significant ice formation, is
considered a mild “spell” between two
great ice ages of the Proterozoic age,
and the late Ordovician age.
The Ordovician Period
• Occurred 490-443 million years ago.
• Was directly after the Cambrian
• Was named by Charles Lapworth in
1879 for the Celtic tribe, the
Ordovices. They rebelled against the
Origin of the Ordovician period
• The boundary between the Cambrian and
Ordovician periods is marked by the appearance
of planktic dictyonemid graptolites.
• The ending boundary of this period is designated
as when black graptolite-bearing shale appear in
• These boundaries were determined by Lapworth
using radiometric dating.
Above is the positioning of the
continents during this period.
Another view is to the right,
showing how North America
and Europe were shaped.
• The Ordovician period is
best characterized by the
presence of diverse marine
• Animals included
trilobites and many other
species that, unfortunately,
were extinct by the end of
the Paleozoic era.
• Once again, green algae
was one of the only forms
of plant life, and was
probably an evolving
point for many other
• The first terrestrial plant,
the liverwort appeared.
• The first fungi appeared in
the late part of this period.
• For most of the period, the
climate was warm and
mild, especially around
the seas. This explains
why marine life thrived.
• The period ended abruptly
with a brief ice age that
consumed much of the
polar regions glacially