Location: British Columbia
Age: Middle Cambrian (505 Ma)
Geological Setting and Age
- During the Middle Cambrian 505 million years
ago, the world was very different. For example, one study suggested
that days lasted only 21 hours and an average year had 417 days.
The theory of plate tectonics, whereby continents are attached
to plates that float on a partly molten layer of the earth known
as the asthenosphere, allows scientists to determine the position
of continents in ancient times. North America did not yet exist,
and the Burgess Shale animals lived on the western edge of a
much more ancient continent known as Laurentia.
- Laurentia, which was composed of what is now North
America and parts of Europe, lay roughly along the equator and
was surrounded by calm seas. There was no significant ice accumulation
in the poles during this time, and that the climate was probably
warmer and more uniform than that of today. Laurentia itself
was likely to be warm because of its equatorial location and
the presence of geological markers, such as evaporites - deposits
that suggest evaporation of water due to high temperature.
- Figure 1. Continental map of Middle Cambrian
earth. Courtesy of the Smithsonian Institution, Washington, D.C.
The only life on the earth at this time existed in the oceans.
Life on land would not evolve for yet at least another 50 million
years. The barren surface was a vast desert, characterized low
topographic relief (i.e., no mountains) and by wind-blown sand,
silt, and clay. The levels of oxygen in the atmosphere, however,
was probably only slightly less than present levels. Warm tropical
reefs predominated on the edges of Laurentia, much of which was
flooded by the large and shallow (epeiric) Sauk Sea. The
Burgess Shale fauna lived a reef with high concentrations of
algae. This implies its local environment was warm shallow water
in the photic zone (light-penetrating zone) because all algae
are photosynthesizers, i.e. require light to make their own energy
food. Since photosynthesizers produce oxygen as a byproduct of
their metabolism, the water was likely highly oxygenated.
The movement of tectonic plates would eventually transport the
Burgess Shale far from its original location. About 175 million
years ago during the Jurassic Period, orogenesis, or mountain
building processes, uplifted the Burgess Shale from the
bottom of the ocean and carried it eastward and northward. These
processes eventually deposited the Burgess Shale in its current
location in Canada.
- Return to Main Page
- Geological Setting
- Flora and Fauna
- References and
Section author: Alexei A. Rivera
This section is part of a Fossil Lagerstätten
web site which has been built up as a result of the efforts of
the 2002-3 MSc
Palaeobiology class in the Department of Earth Sciences at
University of Bristol, as part of a course in Scientific Communication.
Department of Earth Sciences
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