Wednesday, February 15, 2012

Evolution of Rivers

Bull Creek- click to enlarge
I hadn't given much thought to how our rivers were formed until I came across an article in  It turns out that a major factor in their shape and size over millions of years was the evolution of plants. 

Rivers were pretty lackluster affairs 500 million years ago in the Cambrian period, straight, wide and extremely shallow, leaving no discernible banks in the geological record.  How wide were they?  Some estimates are that they were 1000 times as wide as they were deep.  There was no mud yet to support banks.

The first primitive plants developed around 470 million years ago around the time of the development of mud which is more cohesive than sand and gravel.  This wasn't a coincidence as plants are instrumental in the formation of mud.  Acids they produce break down rock and later the development of roots causes physical cracks.  Plant death added to the mud, producing soil.

Soil not only binds the particles together to create firmer banks, but it facilitates the growth of plant roots which holds acts as reinforcement.  When this evolved, we see evidence of meandering streams appeared around 416 million years ago, providing habitat for evolving fish and insects.

By planting trees along streams we enhance the riparian corridor, just our humble way of restoring what nature accomplished millions of years ago before the attack of our plows.


  1. That border of green life on either side of creeks and rivers , I prefer to call the "repair-ian" corridor that protects those channels and the water from many harmful things. I know in green belts , a designated number of feet is enforced. I think it is a good idea to make it a legal standard for every water course.

    1. What a great idea! I will definitely steal it when talking about streams in the future.