During a cardiac cycle, how many of the four chambers contract at any one time?

During a cardiac cycle, TWO of the four chambers contract at any one time. Cardiac cycle refers to the events that occur with every heart beat. The heart is divided into four chamber which are the right and the left ventricles an the left and the right atrium.

Three immediate time scale of earth system are as follow-

Pliocene- this age belongs to the modern Cenozoic er which was of about 3.5 million years old.Miocene- this age appears after Oligocene and before Pliocene, and was bout 16-18 million years old.Oligocene- this age also appeared in the Cenozoic and was about 10-10-12 million years old.

Two long term-time scale of earth system are as follows-

Archaen- Archaen refers to the early proterozoic time, which was of about 1500 million years old. Rocks of Archaen are the oldest.Proterozoic- This refers to the time after Archaen, which was of about 1800-2000 million years old.

The three cycles on earth are as follows-

The rock cycle- Here the rocks transforms from one form to another due to the changing pressure, temperature condition as well as crystallization and sedimentation. The water cycle- Here water is transferred from one place to another, interacting with the atmosphere, lithosphere and the hydrosphere.The carbon cycle- Here transfer of carbon takes place from one place to another.

Volcanoes are formed due to the presence of big mantle plumes as well plate tectonic movement. This activities depicts the on-going various earth processes, how it forms and affects within a system.