Foraminifera are predatory protista with , which is the ultimate source

Foraminifera are predatory Protista with a CaCO3 (Calcium carbonate) shell, which is the ultimate source of Limestone.

Explanation:

Forams or foraminifers are types of protists whose bodies are composed of only single cell. They have a shell or test around their body that is composed on Calcium carbonate (in one specie it is composed of silica).

After their death, the shells accumulate at the bottom of sea to give rise to large deposits of biogenic carbonates specially limestone (CaCO3). This limestone also serves to be a source of Carbon. This process is not rapid and may take millions of years to give rise to considerable rocks and deposits of limestone. This limestone is commercially used by men for a variety of purposes like manufacture of glass, steel etc.

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from my research i have to the conclusion that decomposers, such as fungi, bacteria and invertebrates, play a critical role in nutrient cycling and without them the earth's ecosystem may not support life as we know it. elements such as carbon, nitrogen and phosphorus exist in limited amounts on earth, although huge amounts of carbon are being released into the atmosphere from underground sources now by humans. it is still extremely important that other nutrients be retained by the process of re-use. decomposers are organisms that are able to chemically break down dead material and make these elements available for use by other organisms. without this breakdown of dead material, dead bodies would pile up. so decomposers also play a role in clean up also. without them, life might not continue as we know it and dead material would overwhelm the earth.