Uranium Lead Calculator

Calculator Inputs

Sample Name

206Pb*/238U Ratio

207Pb*/235U Ratio

206Pb*/238U Uncertainty (%)

207Pb*/235U Uncertainty (%)

Common Lead Correction (%)

Discordance Threshold (%)

This educational calculator applies a simplified common lead correction by reducing measured daughter-to-parent ratios by the entered percentage.

Plotly Graph

Example Data Table

Sample	206Pb*/238U Ratio	207Pb*/235U Ratio	Common Lead %	206Pb*/238U Age (Ma)	207Pb*/235U Age (Ma)	Interpretation
Zircon A	0.2500	3.2200	2.00	1430.7	1450.8	Near-concordant
Zircon B	0.1800	2.2400	1.50	1061.7	1180.1	Potential Pb loss
Monazite C	0.3200	4.4800	0.80	1787.9	1730.6	Review discordance

Formula Used

1) 206Pb*/238U age
t_206/238 = ln(1 + R_206/238) / λ₂₃₈

2) 207Pb*/235U age
t_207/235 = ln(1 + R_207/235) / λ₂₃₅

3) Simplified ratio correction
R_corrected = R_measured × (1 − Common Lead % / 100)

4) Approximate age uncertainty propagation
σ_t ≈ σ_R / [(1 + R) × λ]

5) Weighted mean age
t_w = Σ(w_i × t_i) / Σw_i, where w_i = 1 / σ_i²

6) Discordance
Discordance % = |t_207/235 − t_206/238| / max(t_207/235, t_206/238) × 100

The curve shown in the graph is a simplified Wetherill concordia, where x = 207Pb*/235U and y = 206Pb*/238U.

How to Use This Calculator

Enter a sample name for reporting clarity.
Input the measured 206Pb*/238U and 207Pb*/235U ratios.
Enter percentage uncertainties for each measured ratio.
Provide an estimated common lead correction percentage.
Set the discordance threshold used for your screening decision.
Press the calculate button to generate ages and concordance checks.
Review the result table, weighted age, discordance value, and graph.
Use the CSV or PDF buttons to export the current result section.

FAQs

1) What does this calculator estimate?

It estimates uranium lead ages from two isotope systems, reports uncertainty, shows discordance, and gives a simple weighted mean age for quick interpretation.

2) Which isotope systems are used here?

This version uses the 206Pb*/238U and 207Pb*/235U systems because they are the classic paired systems for uranium lead age comparison.

3) Why can the two ages differ?

Differences may reflect lead loss, inherited components, analytical uncertainty, common lead contamination, or disturbance after mineral formation.

4) What is discordance?

Discordance measures how far the two independent ages disagree. Smaller values usually indicate better internal agreement between the two uranium lead systems.

5) Is the common lead correction complete?

No. This page uses a simplified screening correction. Research-grade interpretation often needs measured common lead isotopes, decay disequilibrium handling, and full uncertainty propagation.

6) What does the weighted mean age do?

It combines the two ages using inverse-variance weighting when uncertainties are available, so the more precise age contributes more strongly.

7) How should I read the graph?

The curve is the concordia reference. The sample point should lie near it when both isotope systems agree well after correction.

8) Can I use this for publication work?

Use it for screening, education, and rapid checks. Formal publication decisions should rely on full laboratory reductions and expert geochronology review.