Old Earth Ministries Online Earth History Curriculum

Presented by Old Earth Ministries (We Believe in an Old Earth...and God!)

This curriculum is presented free of charge for use by homeschooling families and schools.

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Chapter 3 - The Cambrian Period

Lesson 14: Cambrian Overview


    The Cambrian is the first geological period of the Paleozoic era, lasting from 542 ± 0.3 million years ago to 488.3 ± 1.7 million years ago; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the classical name for Wales, where Britain's Cambrian rocks are best exposed.




     The Cambrian was a relatively warm period, with temperature averages about 7 degrees C warmer than they are today.  Although it was warm, there is evidence of glaciers being present in the Cambrian.  The earth's atmosphere during this time contained about 13 percent oxygen (compared to 21 percent today).  The greenhouse gas CO2 content of the atmosphere was 4500 ppm, which is more than 11 times the level of today.  The temperature average during the Cambrian was 7° C higher than today.




 Chapter 3: The Cambrian Period


  Lesson 14: Cambrian Overview

  Lesson 15: Supercontinent Gondwana

  Lesson 16: Lagerstätte / Burgess Shale 

  Lesson 17: The Cambrian Explosion Part 1

  Lesson 18: The Cambrian Explosion Part 2

  Lesson 19: The Cambrian Explosion Part 3

  Lesson 20: Species In-Depth: Trilobites



Cambrian Fast Facts


Started:  542 Ma

Ended:  488.3 Ma

Duration:  53.7 Million Years

Preceded By: Ediacaran Period

Followed By: Ordovician Period


Mean atmospheric O2 content over period duration ca. 12.5 Vol %
(63 % of modern level)
Mean atmospheric CO2 content over period duration ca. 4500 ppm
(16 times pre-industrial level)
Mean surface temperature over period duration ca. 21 °C
(7 °C above modern level)
Sea level (above present day) Rising steadily from 30m to 90m



     Reconstructions of Cambrian geography Cambrian Geographysuggest that a global supercontinent, Pannotia, was in the process of breaking up, with Laurentia (North America) and Siberia having separated from the main mass of the Gondwana supercontinent to form isolated landmasses. Most continental land mass was clustered in the southern hemisphere.
     With a lack of sea ice – the great glaciers of the Marinoan
Snowball Earth were long melted – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for thriving life. The sea levels fluctuated somewhat, suggesting that there were 'ice ages', associated with pulses of expansion and contraction of a south polar ice cap.




     Two schemes exists for the stratigraphy of the Cambrian period. The supposedly international (i.e. Western) ICS scheme is in a state of flux, and does not yet have any firmly established internal boundaries, although it has set a stratotype section for the base of the Cambrian, dated quite accurately to 542 ± 0.3 million years ago. In contrast, the Russians and many Chinese scientists prefer a different scheme; since the most significant exposure of Cambrian strata lies in these countries, they are arguably better placed to determine subdivisions.
     Stratigraphy relates to the order of rock units, without referring to their absolute ages (which is chronology). However, because fossils - which are traditionally the cornerstone of stratigrapahy - are relatively rare in the Cambrian, chronology has a significant part to play; if an absolute age can be obtained with a high degree of accuracy for different strata, their relative age can also be established.
     The base of the Cambrian is officially defined as the first appearance of a certain trace fossil, Treptichnus pedum. However, this fossil has recently been found in older rocks than the locality which officially marks the start of the period.  However, there is a period of biological change which makes this time period a good one to demarkate the Cambrian and Precambrian: consensus holds that fossils of the Ediacara biota disappear here, as do some shelly fossils and acritarchs; and a new small shelly fossil biota emerges.



     The Cambrian is unique in its unusually high proportion of lagerstätte. These are sites of exceptional preservation, where 'soft' parts of organisms are preserved as well as their more resistant shells. This means that, paradoxically, our understanding of the Cambrian life surpasses that of later periods.
     The Cambrian period marked a profound change in life on Earth. Before the Cambrian, life was on the whole small and simple. Complex organisms became gradually more common in the millions of years immediately preceding the Cambrian, but it wasn't until this period that mineralised (hence readily fossilised) organisms became common. This diversification of lifeforms was relatively rapid, and is termed the Cambrian explosion. This explosion produced the first representatives of most modern phyla, but on the whole, most Cambrian animals look alien to today's eyes, falling in the evolutionary stems of modern groups. While life prospered in the oceans, the land was barren - with nothing more than a microbial 'crud' gracing the soils. Apart from tentative evidence suggesting that some animals floundered around on land, most of the continents resembled deserts spanning from horizon to horizon. Shallow seas flanked the margins of several continents, which had resulted from the relatively recent breakup of the preceding supercontinent Pannotia. The seas were relatively warm, and polar ice was absent.

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Source Pages: Cambrian Period, Stratigraphy of the Cambrian