The Periodic Table of the Elements
Top left: water (Υ)
Top right, disconnected from the rest: air (Α)
Bottom left: Fire (Π)
Bottom right (but farther left than air): Earth (Γ)
[This arrangement of the elements is similar to the first four elements of the periodic table, and the same as the original comic.]
Caption: You can spot an outdated science textbook by checking the bottom of the periodic table for missing elements. For example, mine was published in ancient Greece.
Title text: If you have a periodic table new enough to have carbon, you can look at its atomic weight. On older tables, some of the carbon-14 will have decayed, making carbon's atomic weight lower.