Emiliana huxleyi has a golden-yellow, free-swimming form and a resting stage, which is spherical and covered with uniquely patterned calcite plates. For many years, scientists thought the two were different organisms, classifying the active form as a haptomonad and the resting stage as a coccolithophorid. Like some other protists, Emiliana huxleyi can multiply very quickly in favorable conditions, when it accounts for up to 90 percent of the phytoplankton. These blooms cover areas of up to 38,600 square miles (100,000 square km) and are visible from space because they turn the water from deep blue to milky turquoise, as seen here in a satellite image taken of the coast off Cornwall, UK. The coccolithophorids cause the change in color of the water because the calcite plates act like mirrors reflecting the incoming sunlight. Emiliana huxleyi have been found worldwide in chalk deposits dating from 65 million years ago. Chemicals called alkenones are present within the fossils and are used to gather information about sea surface temperatures in the past.