Radioactive Elements - WIll there be any effect on earth or an oceanic world if its crust and mantle lack Radioactive Elements?

Question

As the title says... What would be the effect to earth or an oceanic planet if it lacks the presence of Radioactive Elements in its crust and mantle.

Also can you explain what would happen if we don't have Radioactive Elements in core?

Answer 1

Radioactive materials contributed a significant amount of heat to the Earth's interior and may have been responsible for the melting of the Earth's core.

No Plate Tectonics - Earth will be colder

Heat from radioactive decay provides the energy driving the planet's plate tectonics. Without plate tectonics, the Earth's water and other volatiles (like carbon dioxide) are gradually lost to the interior of the planet. Without water and and carbon dioxide to drive the greenhouse effect, the Earth would be MUCH COLDER.

Right now, the warming influence is literally a matter of life and death. It keeps the average surface temperature of the planet at 288 degrees kelvin (15 degrees Celsius or 59 degrees Fahrenheit). Without this greenhouse effect, the average surface temperature would be 255 degrees kelvin (-18 degrees Celsius or 0 degrees Fahrenheit); a temperature so low that all water on Earth would freeze, the oceans would turn into ice and life, as we know it, would not exist.

Weakened Magnetic Field

If you assume the Earth had all the radioactive elements in the past and those have all decayed, then nothing much would happen immediately. However, the core of the Earth would solidify at a much more rapid pace (since the decay would not be contributing to the Earth's heat inventory.

A drier world

A weakened magnetic field would have lead to a faster loss of water dissociation and loss of the freed hydrogen. This could have lead to a much drier world.

Without plate tectonics to pump water lost into the crust back into the atmosphere, all water eventually becomes trapped deep in the crust (or lost to space).

NOTE: It is thought that our oceans are both replenished by plate tectonics and required for the planet's plate tectonics to work.

Not much from a chemical perspective

Transuranic elements do not contribute much to the mineral inventory of the surface. A lack of Transuranic elements wouldn't be noticed from a chemical perspective.

Not much from a radiation dosage perspective

There are two primary sources of background radiation at the Earth's surface. One source derives from the decay of long-lived radioactive isotopes (like transuranics) and the biggest contributor is Radon gas.

The biggest source of natural background radiation is airborne radon, a radioactive gas that emanates from the ground. Radon and its isotopes, parent radionuclides, and decay products all contribute to an average inhaled dose of 1.26 mSv/a (millisievert per year).

However, an individual dose can be up to 500x this dose depending upon local conditions.

If you completely remove this exposure mechanism, most humans are still exposed to cosmic rays. Cosmic rays are high speed particles traveling through space and though to be launched by high-energy events like supernovae, neutron star mergers, black hole formation, etc.

The Earth and all living things on it are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from protons to iron and larger nuclei derived sources outside our solar system. This radiation interacts with atoms in the atmosphere to create an air shower of secondary radiation, including X-rays, muons, protons, alpha particles, pions, electrons, and neutrons. The immediate dose from cosmic radiation is largely from muons, neutrons, and electrons, and this dose varies in different parts of the world based largely on the geomagnetic field and altitude. This radiation is much more intense in the upper troposphere, around 10 km altitude, and is thus of particular concern for airline crews and frequent passengers, who spend many hours per year in this environment. During their flights airline crews typically get an extra dose on the order of 2.2 mSv (220 mrem) per year.

No nuclear power

All of our nuclear fission powered reactors use Uranium or Transuranics. So no fission power. No nuclear bombs (either fission or fusion).

Answer 2

Two main results.

1) No magnetic field. Without radioactive decay to keep the interior hot, after a few 10s of millions of years the core of the earth will become "frozen", that is, no longer liquid. With a solid core there will be no currents to flow and produce a magnetic field. This will mean no shielding from solar radiation. Also, no northern (or southern) lights. Say goodbye to the ozone layer, too.

2) No plate tectonics. With the core solid, the mantle will become likewise solid. This means no volcanoes and no mountain-building. Once a mountain gets eroded (which will take a few 10s to 100s of millions of years), no replacement will get pushed up.

It is useful to compare the volume of the world's oceans with the volume of the land above sea level. Ocean volume is about 1335 million cubic kilometers. The total land area is about 149 million square kilometers, with an average height of about 840 meters, for a total volume of 125 million cubic kilometers. As result, erosion would ultimately sweep all of the land into the sea.

The earth would be a water world, with only coral reefs providing dry land, except for the occasional ring walls thrown up by major asteroid impacts. This reef area might be quite large, since I suspect that, once a landmass was under water the erosion processes carrying silt into the abyssal deeps would be quite slow. Nevertheless, there will be no mountains, and probably no relief greater than 10 meters.

Answer 3

As it hasn't been brought up yet:

Less diversity resp. slower or even no evolution.

Humanity did evolve as fast as we did because of all the radioactivity around us forcing more mutations over generations. Were there way less or even no radioactivity on earth there would likely be no species more evolved than some plancton, polyps and similar. Maybe plant life, and some animals. but certainly no humans or similar.