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Carbon dating is a method of estimating the age of materials. This method, developed by Willard F. Libby can date samples that are as old as $50,000$ years. It has proven to be useful in archaeology, geology, geophysics, and other branches of Science. Carbon dating is based on the fact that plants and animals contain carbon in a ratio that matches the percentages found in the atmosphere for as long as they are alive. This is true because most life on Earth is carbon-based; plants absorb it through photosynthesis and animals absorb it by eating plants or animals that eat plants. Once an organism dies, the carbon intake stops, and the percentage of carbon-$14$ decreases. To calculate the date of an object, researchers compare the percentage of carbon-$14$ it contains to the normal percentage found in the atmosphere. The lower the ratio, the older the object. Do you ever wonder how the age of ancient tools, bones and other materials is determined? 

Historians have classified historical periods into               parts. 

The term BCE stands for Before Christian Era

CE refers to _____.

Use the picture to answer the questions.

What is shown in the picture?

What do the paintings of early human beings depict?

Use the picture to answer the questions.

Where are these types of paintings usually found? 

Humans began producing crops through long _____ and with human _____.