Download Fossil stromatolites constitute our earliest record of life on Earth

Cyanobacteria
What is cyanobacteria?
Cyanobacteria are aquatic,
photosynthetic bacteria.
Because they are bacteria, they are
quite small and usually unicellular,
though they often grow in colonies
large enough to see.
Cyanobacteria have the distinction of
being the oldest known fossils, more
than 3.5 billion years old!
It may surprise you to know that
cyanobacteria are still around. They
are one of the largest and most
important groups of bacteria on
earth.
Stromatolites
What are stromatolites?
Fossil stromatolites constitute our
earliest record of life on Earth.
Although many stromatolites are
fossils, there are a number of
locations on the modern-day earth
where stromatolites are still forming.
How do they form?
The cyanobacteria form colonies and
trap sediment with their sticky
surface coatings.
The trapped sediment reacts to
calcium carbonate in the water to
form limestone.
These limestone deposits build up
very slowly.
It can take a stromatolite 100 years
to grow 5 cm.
A 1 meter-high stromatolite might be
2,000 years old!
Diatoms
Diatoms are a major group of algae,
and are one of the most common
types of phytoplankton.
Most diatoms are unicellular.
A unique feature of diatoms is that
they are encased within a cell wall
made of silica.