The period spans the time from the end of the pliocene epoch 1.8 million years ago to the present.

1.tertiary
2.quaternary
3.cretaceous
4.triassic

The current period is the Quaternary period.

The Quaternary period began a little over two and a half million years ago and is divided into two epochs, the Pleistocene and Holocene epochs. The Pleistocene epoch ended about 11,500 years ago and currently we are living in the Holocene epoch. These are all divisions that are used to divide the earth's history with reference to certain events and time frames.

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You should never redesign your experiment. try and see what in your experiment you made a mistake on or try and test your experimemt with somebody else. see if they get the right results.