Mississippi Science ESS.2B.3

ScienceGrades 9–12Earth and Space Science

The Standard

ESS.2B: Students will develop an understanding of the history and evolution of the earth.

Use mathematical concepts to calculate the absolute age of Earth materials using actual or simulated isotope ratios.

2026 Mississippi College- and Career-Readiness Standards for Science · Earth Structure and History

Teacher's field guide

What Students Need to Do: Students use parent and daughter isotope counts to find how many half-lives have passed. They multiply that number by the isotope’s half-life to calculate a mineral’s age.
What Mastery Looks Like: Given a closed sample with no daughter atoms at formation, they trace 80 parent atoms to 40, then 20. With a 100-million-year half-life, they calculate an age of 200 million years.
Common Misconceptions: Students may read a 1:3 parent-to-daughter ratio as three half-lives instead of two. They may also count daughter atoms that were present when the mineral formed.
How to Assess It: Exit ticket: A closed mineral started with no daughter atoms. It now has 20 parent atoms and 60 daughter atoms. If the half-life is 100 million years, how old is it? Show the halving steps.

Lesson moves

Start with 16 parent-isotope counters; flip half to daughter counters each round, then label each round as 100 million years.
Ask students to sketch why a 1:3 parent-to-daughter ratio means two half-lives, not three.
Give pairs ratio cards labeled 8:0, 4:4, and 2:6; partners match each to zero, one, or two half-lives.
Show a meteorite photo and give a simulated 1:1 uranium-238 to lead-206 ratio; students estimate its age using a 4.5-billion-year half-life.

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A ready-to-print activity worksheet aligned to ESS.2B.3, with an answer key for the teacher on its own page. No account needed.

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