They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[1] The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.

In addition to the stable species, calcium and barium each have one extremely long-lived and primordial radionuclide: calcium-48 and barium-130, with half-lives of 5.6×1019 and 1.6×1021 years, respectively.

Apart from the 21 stable or nearly-stable isotopes, the six alkaline earth elements each possess a large number of known radioisotopes.

None of the isotopes other than the aforementioned 21 are primordial: all have half lives too short for even a single atom to have survived since the solar system's formation, after the seeding of heavy nuclei by nearby supernovae and collisions between neutron stars, and any present are derived from ongoing natural processes.

Beryllium-7, beryllium-10, and calcium-41 are trace, as well as cosmogenic, nuclides, formed by the impact of cosmic rays with atmospheric or crustal atoms.

Strontium-90 is produced in appreciable quantities in operating nuclear reactors running on uranium-235 or plutonium-239 fuel, and a minuscule secular equilibrium concentration is also present due to rare spontaneous fission decays in naturally occurring uranium.

[33] The longest lived isotope of radium is radium-226 with a half-life of 1600 years; it along with radium-223, -224, and -228 occur naturally in the decay chains of primordial thorium and uranium.

This thermonuclear rate-limiting bottleneck is the reason most main sequence stars spend billions of years fusing hydrogen within their cores, and only rarely manage to fuse carbon before collapsing into a stellar remnant, and even then merely for a timescale of ~1000 years.

The incorporated radionuclides inflict significant damage to the bone marrow over time through the emission of ionizing radiation, primarily alpha particles.

"Earth" was a term applied by early chemists to nonmetallic substances that are insoluble in water and resistant to heating—properties shared by these oxides.

[45] Magnesium was first produced by Humphry Davy in England in 1808 using electrolysis of a mixture of magnesia and mercuric oxide.

Later in the 18th century, William Withering noticed a heavy mineral in the Cumberland lead mines, which are now known to contain barium.

[52][53] While studying uraninite, on 21 December 1898, Marie and Pierre Curie discovered that, even after uranium had decayed, the material created was still radioactive.

The material behaved somewhat similarly to barium compounds, although some properties, such as the color of the flame test and spectral lines, were much different.

[59] Magnesium and calcium are very common in the Earth's crust, being respectively the fifth and eighth most abundant elements.

[68] Beryllium alloys are used for mechanical parts when stiffness, light weight, and dimensional stability are required over a wide temperature range.

Its low atomic weight and low neutron absorption cross-section would make beryllium suitable as a neutron moderator, but its high price and the readily available alternatives such as water, heavy water and nuclear graphite have limited this to niche applications.

In the FLiBe eutectic used in molten salt reactors, beryllium's role as a moderator is more incidental than the desired property leading to its use.

[4][61][81] Radium has many former applications based on its radioactivity, but its use is no longer common because of the adverse health effects and long half-life.

[83] The nuclear quackery that alleged health benefits of radium formerly led to its addition to drinking water, toothpaste, and many other products.

[71] Radium is no longer used even when its radioactive properties are desired because its long half-life makes safe disposal challenging.

In laboratory, they are obtained from hydroxides: or nitrates: The oxides exhibit basic character: they turn phenolphthalein red and litmus, blue.

Salts Ca and Mg are found in nature in many compounds such as dolomite, aragonite, magnesite (carbonate rocks).

Excessive amounts of strontium-90 are toxic due to its radioactivity and strontium-90 mimics calcium (i.e. Behaves as a "bone seeker") where it bio-accumulates with a significant biological half life.

Beryllium's low aqueous solubility means it is rarely available to biological systems; it has no known role in living organisms and, when encountered by them, is usually highly toxic.

The next alkaline earth metal after radium is thought to be element 120, although this may not be true due to relativistic effects.

[88] The synthesis of element 120 was first attempted in March 2007, when a team at the Flerov Laboratory of Nuclear Reactions in Dubna bombarded plutonium-244 with iron-58 ions; however, no atoms were produced, leading to a limit of 400 fb for the cross-section at the energy studied.

[89] In April 2007, a team at the GSI attempted to create element 120 by bombarding uranium-238 with nickel-64, although no atoms were detected, leading to a limit of 1.6 pb for the reaction.

This noticeably contrasts with periodic trends, which would predict element 120 to be more reactive than barium and radium.