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4600 Mya
Formation of the Earth

The Solar System as a whole started as a huge disc of material slowly rotating. Hydrogen and helium were derived from the original Big Bang some 14 billion years ago. The other heavier elements were derived from the debris of exploding stars – Supernovae – where they had been formed by heat and pressures. The formation of the disc and its rotation were probably instigated by a the effects of a nearby Nova.

This rotating disc of debris became centred around a core which became heavier and more dense as gravity pulled in more material. In the end, it was so dense and hot that the hydrogen atoms became fused together to form Helium. This process known as atomic fusion powers the sun and gives us all light and heat.

This used up about 50% of the debris. The rest slowly accreted into the planets as we know them today.

The Earth cooled and the dense heavier metals sank to the centre of the Earth forming its Core – mainly molten Iron & Nickel. the majority of the planet is taken up by the mantle, which is where lava and magma that we see in volcanoes comes from.

The origin of the water on Earth is an intricate part of the story too.

There are a 2 main theories on the origin of the oceans, and indeed all water on the planet. The earliest evidence for water is from around 3,800 million years ago (Mya), when in what is now northern Canada and Greenland, lava was extruded underwater and formed what are known as “pillow lavas” identical to those at present being formed in places like Hawaii.

In fact in the Barberton Mountainland in Mpumalanga pillow lavas dated at 3,500 Mya can be seen.

So we know there was water on the surface of the Earth from these times.

So where did it come from?

There are many questions still to be answered, but it appears that there are 2 main theories on the derivation of the water. These are not mutually exclusive and, as ever, a combination of the 2 is feasible in varying proportions.

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The first is that water was derived from the impacts of comets, meteorites and asteroids early in the process of Earth’s formation. Comets are often described as “dirty snowballs” as they largely consist of ice. Various types of meteorites also have water within them. However, with the present knowledge of the amounts of these comets and meteorites that would have been present then, there is too much water on the Earth’s surface, and it would have taken too long for the water to accumulate just from this process.

The second theory – called ‘outgassing’ or ‘degassing’ maintains that as the Earth accumulated from the planet forming disc around the young sun, particles of ice would have been included in the mass that came to be the planet. Then, during the subsequent heating of the planet – largely by impacts of more asteroids and debris- the water was emitted as steam which then condensed and fell as rain. Over time this accumulated in the low-lying areas as oceans. Water vapour is emitted by volcanic action to this day.

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This process is most likely the origin of the oceans. But, of course, it puts forward the notion that there was ice in the planetary debris from which the earth formed, but is this not the source of the ice in asteroids, comets and meteorites that also contributed to the oceans?

Thus our 2 possible theories may not be far apart at all.

This water would not of course, be ‘salty’ as our seas are today. The salt in our seas is derived from the erosion of rocks by rain and rivers, and brought down to the sea where it has been concentrating for a long time. In fact, this process of changing from ‘fresh’ to ‘salty’ water was used in the 18th century in an attempt to calculate the age of the Earth. By measuring the salt content of rivers and calculating how long it would take to get the amount of salt contained in all the oceans. The method failed as the total mass of the oceans was not known and seriously underestimated!

4600 Mya Formation of the Earth

Further reading

4600 Mya
Formation of the Earth