A group of living things
Kelp, diatoms and kin
SAR supergroup
Giant kelp forests, and tiny glass shells that make much of our oxygen
Its members' last common ancestor lived about 1.4 billion years ago.
You and kelp, diatoms and kin last shared an ancestor about 1.8 billion years ago (on 28 July, if life's history were one year).
This huge, little-known branch of life holds both giant seaweeds and glass-shelled plankton. Its tiny diatoms make about a fifth of the oxygen we breathe. Giant kelp, about as long as three buses, and diatoms, many smaller than a grain of sand, are relatives in one group, sitting apart from plants on one side and animals and fungi on the other.
Giant kelp grips bare rock and grows rope-like stalks to about 30 metres long towards the light. Each stalk carries long, leaf-like blades held up by round air bladders, joining into a floating canopy that feeds and shelters thousands of species of fish and other sea life. It looks like a plant, but it is algae, with no true roots, stems or leaves.
Diatoms are single cells that live in sunlit oceans, lakes and waterways. Each lives inside a clear glass box in two halves, one fitting over the other like a pill box. Together they soak up about a fifth of the planet's carbon dioxide and sit at the base of the ocean's food chains.
Super-fast grower
In perfect seas, giant kelp can grow about 45 centimetres in a single day, longer than a school ruler.
In your ice cream
Giant kelp has been picked from California waters since the early 1900s. It has long been used to make everyday things like ice cream and toothpaste.
Relatives in the pyramids
The Giza pyramids are partly built from stone packed with fossils of single-celled relatives of kelp that grew to several centimetres wide.