<P> Archaeans, bacteria, and eukaryotes continued to diversify and to become more complex and better adapted to their environments . Each domain repeatedly split into multiple lineages, although little is known about the history of the archaea and bacteria . Around 1.1 Ga, the supercontinent Rodinia was assembling . The plant, animal, and fungi lines had split, though they still existed as solitary cells . Some of these lived in colonies, and gradually a division of labor began to take place; for instance, cells on the periphery might have started to assume different roles from those in the interior . Although the division between a colony with specialized cells and a multicellular organism is not always clear, around 1 billion years ago, the first multicellular plants emerged, probably green algae . Possibly by around 900 Ma true multicellularity had also evolved in animals . </P> <P> At first, it probably resembled today's sponges, which have totipotent cells that allow a disrupted organism to reassemble itself . As the division of labor was completed in all lines of multicellular organisms, cells became more specialized and more dependent on each other; isolated cells would die . </P> <P> Reconstructions of tectonic plate movement in the past 250 million years (the Cenozoic and Mesozoic eras) can be made reliably using fitting of continental margins, ocean floor magnetic anomalies and paleomagnetic poles . No ocean crust dates back further than that, so earlier reconstructions are more difficult . Paleomagnetic poles are supplemented by geologic evidence such as orogenic belts, which mark the edges of ancient plates, and past distributions of flora and fauna . The further back in time, the scarcer and harder to interpret the data get and the more uncertain the reconstructions . </P> <P> Throughout the history of the Earth, there have been times when continents collided and formed a supercontinent, which later broke up into new continents . About 1000 to 830 Ma, most continental mass was united in the supercontinent Rodinia . Rodinia may have been preceded by Early - Middle Proterozoic continents called Nuna and Columbia . </P>

Which event occurred first in the earth's history