New Hampshire Geology New Hampshire Bedrock Map

Ordovician Period (490-433 million years ago)

Same Old, Same Old....

During the Ordovician Period [oar-doh-VISH-ee-in], which lasted about 47 million years, the Taconic Orogeny and the accretion - or 'pasting-on' - of the Bronson Hill Complex on the eastern shore of the Connecticut River Valley, continued.  These events were caused by the fact that the early North American craton, Laurentia, was colliding with Baltica - the European craton.  (Both of these events are described in the "Cambrian Period" pages found on the Geologic Timeline at left.)  Together with the preceeding Cambrian Period, the Ordovician Period was known as the 'Age of Invertebrates'.  Invertebrates are animals without backbones, such as snails and clams.

Most of what would become New Hampshire at this time was part of a small plate known as 'Avalonia'.  Avalonia was made up of what would one day be New England, Nova Scotia and the British Isles.  New Hampshire, and the rest of Avalonia, had drifted north and west from its position near the South Pole during the Cambrian Period.  It now rested in the Mid-Southern latitudes, nearly halfway to the Equator in the Southern Hemisphere.

Something Fishy's Goin' On

The fact that the Ordovician period was part of the 'Age of Invertebrates',  meant that invertebrates were the dominant animal type, not the only one.  In fact, it was during this period that  the first vertebrates (animals with backbones) started to show up in the fossil record.  [FYI - the individual bones in your spine are known as vertebra.]  Among the first vertebrates to show up were fish.

It Isn't Easy Being Green

At this point, we are just past the 90 percent mark in Earth's Geologic History.  To date, there had been no plants or animals living on the dry land surface of the planet.  This was about to change.  As mentioned in the Cambrian Period, for most of Earth's history the dominant life form on Earth was single-celled anearobic bacteria.  Over time, cyanobacteria (formerly known as blue-green algae) and ocean living plants developed .  Blue-green algae and plants produced oxygen as a by product of photosynthesis - which turned out to be poisonous to the original anaerobic bacteria.  Over millions and millions of years, the blue-green algae and plants multiplied while bacteria slowly died out from the increase in oxygen.  The oxygen increased not only in the oceans, but also in the atmosphere.

As plants increased their presence in the oceans, it was only a matter of time before they started straying onto land, most likely in the intertidal zone.  The intertidal zone is that area of the shoreline that lies between the high and low tide water levels.  Sometimes this zone is under water and sometimes it is exposed to the air.

Welcome to Avalonia!

NH ordovician map

New Hampshire was once part of a small tectonic plate  that was separate from North America.  This small plate was known as Avalonia and included what today is Nova Scotia and the British Isles!

(Click on the image for a closer look.)
Image Credit: Christopher Scotese; www.scotese.c

In The Zone

intertidal_zoneThe intertidal zone is where biologists believe the first land plants made their appearance during the Ordovician Period.

(Click on the image for a closer look.)
Image Credit: Daniel E. Reidy

 Squishy or Fishy ?

Invertebrates, (animals without backbones) such as jellyfish, sea slugs and shellfish, were the dominant animal type during the Ordovician Period.  However, fishes and other vertebrates (animals with backbones) started to make their appearance in the fossil record at this time.

 Did You Know?

The Ordovician Period is named after a Celtic tribe called the Ordovices.