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Isotopes

Isotopes

Elements have a set number of protons that determines their atomic number (Z). For example, all atoms with eight protons are oxygen; however, the number of neutrons can vary for atoms of the same element. The sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are called isotopes. Elements can have multiple isotopes, for example, carbon-12, carbon-13, and carbon-14.An element's atomic mass, or weight, is a...

Conditions on Early Earth

Conditions on Early Earth

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen into the primordial atmosphere. However, organisms with the characteristics of life were not initially present on earth. Scientists have used experimentation to determine how organisms evolved that could grow, reproduce, and maintain an internal environment.

Radioactivity and Nuclear Equations

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for hydrogen, neutrons. The number of protons in the nucleus is called the atomic number (Z) of the element, and the sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are isotopes of the same element.
A nuclide of an element has a specific number of protons and...

Radioactive Decay and Radiometric Dating

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. The number of disintegrations per unit time is called the activity (A), which is directly proportional to the number of nuclei in the sample. The decay constant (λ) is an average probability of decay per nucleus in unit time.

Conditions on Early Earth

Conditions on Early Earth

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen into the primordial atmosphere. However, organisms with the characteristics of life were not initially present on earth. Scientists have used experimentation to determine how organisms evolved that could grow, reproduce, and maintain an internal environment.

Isotopes and Radioisotopes

Isotopes and Radioisotopes

In the early 1900s, English chemist Frederick Soddy realized that an element could have atoms with different masses that were chemically indistinguishable. These different types are called isotopes — atoms of the same element that differ in mass. Isotopes differ in mass because they have different numbers of neutrons but are chemically identical because they have the same number of protons. Soddy was awarded the Nobel Prize in Chemistry in 1921 for this discovery.
An isotope containing more...

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Related Experiment Video

Updated: Jul 20, 2026

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

Published on: June 13, 2015

Modelling the isotopic evolution of the Earth.

Debajyoti Paul¹, William M White, Donald L Turcotte

¹Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, USA.

Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences

|December 4, 2002

Summary

This study introduces a new Earth model that simulates geochemical processes and isotope evolution. The model successfully replicates lead isotope data in the upper mantle, challenging previous assumptions about its depletion over time.

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Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

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Atom Probe Tomography Analysis of Exsolved Mineral Phases

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Published on: October 25, 2019

Area of Science:

Geochemistry
Isotope Geochemistry
Earth System Science

Background:

Understanding Earth's geochemical evolution requires accurate modeling of isotope systems.
Previous models have struggled to replicate the observed lead isotope systematics of the depleted upper mantle.

Purpose of the Study:

To develop a flexible multi-reservoir forward-transport model of Earth.
To incorporate Sm-Nd, Rb-Sr, U-Th-Pb-He, and K-Ar isotope-decay systematics.
To reproduce the Pb-isotope systematics of the depleted upper mantle, a key challenge for prior models.

Main Methods:

Developed a multi-reservoir forward-transport model of Earth.
Utilized differential equations to simulate nuclide abundance changes over geological time.
Incorporated fluxes keyed to heat production and constrained by present-day estimates and reservoir sizes.
Used 'enrichment factors' to link elemental transport to fluxes, allowing for fractionation.

Main Results:

Successfully reproduced the Pb-isotope systematics of the depleted upper mantle, attributing it to U and radiogenic Pb subduction from the continental crust.
Replicated observed Sr, Nd, Ar, and He isotope ratios in the atmosphere, continental crust, and mantle.
Demonstrated that both steady-state and time-variant incompatible-element concentrations in the continental crust and upper mantle are possible.
Showed that incompatible-element concentrations can increase over time in the depleted mantle, invalidating assumptions of progressive depletion or steady-state.

Conclusions:

Assumptions of a progressively depleting or steady-state upper mantle are not supported by the model.
Early rapid depletion of the upper mantle in incompatible elements is a ubiquitous feature, making a near-chondritic Th/U ratio in the Archean upper mantle unlikely.
The optimal K/U ratio for the bulk silicate Earth is suggested to be around 10,000.