What is meant by geological time scale? Why is it necessary to determine the age of fossils ?

Explanation

### Step-by-Step Solution

**Step 1: Definition of Geological Time Scale**
The geological time scale (GTS) is a system used by geologists and paleontologists to describe the timing and relationships of events in Earth's history. It is a chronological framework that divides Earth's history into various segments, including eons, eras, periods, epochs, and ages. This scale helps scientists understand the sequence of geological and biological events over time.

**Step 2: Structure of Geological Time Scale**
The geological time scale is organized into three major eras:
- **Cenozoic Era**: The most recent era, which includes the rise of mammals and birds.
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