What’s on the van? – Stromatolite

This week’s What’s on the van? comes from Dr Tracy Aze, Museum of Natural History Research Fellow.

This rock called a stromatolite (from the Greek strōma, meaning mattress or bed and lithos meaning rock) is from a very old suite of rocks called the Porsanger Dolomite Formation in Norway, and is at least 542 million years old.

Stromatolites are produced by the activity of ancient blue-green algae, otherwise known as cyanobacteria. The algae are photosynthetic and need good light conditions to allow them to photosynthesise, consequently they live in shallow waters where sunlight can penetrate. They grow in thin mats on the sea floor, which helps them maximise the amount of light they receive. Over time these mats are covered by sediment grains, which block the sunlight and the algae move up through the sediment layer as they migrate back towards the light. This process happens time and time again over many years and the layering that can be seen in this rock is built up as a result.

The algae that produce stromatolites represent some of the earliest life forms on Earth and some deposits have been dated at 3.5 billion years old! Although they are some of our most primitive life forms, communities of these types of algae can still be found living today in shallow warm waters in places such as Western Australia and The Bahamas and visiting these places is thought to be bit like looking through a window to our distant geological past.