Cambrian Period page 1
(540-490 million years ago)

Spineless Critters First

The Cambrian Period is the time in Earth's history when more new varieties of life forms developed than at any other time.  Together with the Ordovician (oar-doh-VISH-ee-in) Period, this was known as the 'Age of Invertebrates'. Invertebrates are animals without backbones, such as snails and clams.

The first creatures with hard parts (shells and skeletons), and most of our familiar animal types develop at this time.  For all this new development, there are still no plants or animals on land yet.

 This time of rapid innvertebrate development is sometimes referred to as the 'Cambrian Explosion'.  It is also known as the 'Age of Trilobites'.  Trilobite fossils start to show up all over the world in rocks that date to this time period.  But remember, NH has no 'good' fossils, because we have no sedimentary rocks.  We had sedimentary rocks here…what happened to them?  There are trilobites in Maine and Massachussetts rocks.
(see: http://www.gsmmaine.org/)

During this time, most of the tectonic plates were gathered together into a continent known as Gondwana.  The 'land' that would one day be New Hampshire was ocean floor, near the South Pole, and off the coast of what would become South America! (See map at right.)

Poisonous Air?

For most of the 2 billion or so years before the Cambrian Period (known as the Precambrian Period), life on Earth was limited to single celled anaerobic bacteria living in the oceans.  Anearobic means that no oxygen was used or made by the bacteria.  In fact, these bacteria survived best without oxygen.  The atmosphere at that time had  very little oxygen in it.  In fact, you wouldn't have been able to breathe the Earth's air at that time and survive.

Towards the end of the Precambrian Period, a new kind of bacteria - cyanobacteria [sigh-ANN-oh bak-teer-ee-uh] (formerly known as blue green algae) was developing in the oceans.  Cyanobacteria tried something new:  it used the Sun's energy, combined with nutrients in the water, to make a kind of sugar.  This sugar was used as an energy source (food) for the cyanobacteria to grow and reproduce.

This was the introduction of photosynthesis ('photo' meaning 'light' and 'synthesis' meaning 'to make from'.)  Photosynthesis produces carbon dioxide for plants to use and gives off oxygen as a waste product. Pure oxygen happens to be poisonous to anaerobic bacteria.

This was unfortunate for the anaerobic bacteria, but fortunate for us! 

Over time, more and more cyanobacteria populated the Earth, causing the share of oxygen in the atmosphere to  increase.  The development of cyanobacteria made it possible for photosynthetic plant life to prosper.

Today, oxygen makes up about 21% of the Earth's atmosphere and the anaerobic bacteria is reduced to living in places where oxygen is scarce and conditions make it hard for other organisms to survive.  They continue to live in mud, boiling hot springs and in sediments at the bottom of the ocean.

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