The Earth is incomplete work in progress

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

19 December 2021

Clear definitions are very important in science. School children, for example are taught that the speed of sound is 330 metres per second. This is grossly inaccurate because the value greatly depends on the medium of travel. Even in air, the speed of sound varies depending on the temperature and pressure – hence on altitude. It is about 340m/s at sea level and 300m/s at around the cruising altitude of a jumbo jet – 10,000m above seal level.

I thought about this recently when some one asked me this seemingly simple question: how old is the earth? I replied with a question: what do you mean? To which he responded with: how long ago was it formed? My answer to that was: “it is still forming! So, we can’t really say ‘when it was formed’”

That might sound perplexing, especially because many sources will say that the earth formed about 4.5 billion years ago. Unfortunately, when we hear that, we immediately assume that the formation happened at an instant – like a big bang.

Well, it turns out that the formation of a planet is a very slow process that takes billions of years and it is still going on even today. The origin of our planet was a big cloud of gases, dust and rocks moving around the sun.

Then, the bigger rocks attracted the smaller ones via gravity. The bigger they got, the stronger their gravitation strength and eventually, one dominant mass remained and it continued attracting the other smaller ones as it moved round the sun.

Over the last 4.5 billion years, the earth has swept most of the dust and rocks on its path and also captured stray objects that happen to come too close to it on their journey from wherever to wherever. These are the asteroid impacts.

If you look up at night you will notice a few shooting stars streaking across the sky. These are small rocks [pebbles] being sucked up by the earth from its path. Every day about 50 tonnes of these particles are swept in by our planet. This comes to almost 20,000 tonnes of additional mass every year.

So, can we really say that the formation of the earth is complete when each year, its mass increases by about 20,000 tonnes? Furthermore, its shape is also constantly changing – continents drifting, mountains, valleys and lakes forming. Clearly, our home planet is work in progress!