Carbon "Locked Away"

One of the things that stromatolites and other photosynthetic organisms have done over time has been to "lock away" carbon.  They remove carbon dioxide during photosynthesis:

These carbohydrates have been used to:

1. Make more biomass (plant mass or growth)
2. Enrich the soil with organic matter
3. Removed carbon long term and be stored as coal underground.

In addition, carbon dioxide is removed when it dissolves on sea water.  It is combined with calcium by many mollusks and corals to make calcium carbonate or limestone.  

When the reef is buried or compressed the process of limestone formation is complete.  This kind of removal is another long term storage way of storing carbon and keeping locked out of the atmosphere.

It is fortunate that we have this means of removing carbon (especially carbon dioxide) out of the atmosphere and storing long term (i.e. 10's or 100's of millions of years). It is this reason that the planet has had a stable climate for so long.  If this hadn't happened Earth may have shared the same fate as Venus with a runaway greenhouse effect and surface temperatures over  400 Celcius.