Geologically Important Radioactive Elements Used for Radiometric Dating

Two editions. The 2024 edition of the Reference Tables was used for the June 2025 through August 2026 Regents examinations, and the past questions on this site were written for it. The 2026 Revised edition applies from the January 2027 exam onward, so a student preparing for January 2027 or later should practise with the 2026 Revised edition.

This site does not copy the reference tables. Open them on the NYSED website with the links below.

The two editions side by side

What changed in the 2026 Revised edition

• Moved: 'Geologically Important Radioactive Elements Used for Radiometric Dating' is on page 15 in 2024 (rotated page) and page 12 in 2026 (upright, with isotope symbols added).
• Radiometric dating table: Rubidium-87 half-life 48.8 billion to 49.7 billion years; Uranium-235 half-life 713 million to 703 million years; Samarium-147 datable materials now add lunar fragments and meteorites; column headings reworded ('Materials That Can be Dated', 'Approximate Half-life').

The editions were compared by eye on page images, so a small change in a number may be missed. The full list of differences is on the reference tables page.

Past questions that use this table

• January 2026, question 11 Which statement identifies the evidence used to determine when the Huronian ice age occurred?
• January 2026, question 26 Which three claims provide correct interpretations from data collected at Hommelstø?

Topics that use this table

• Formation and early history of Earth
• Radiometric dating and half-life