Henry Gee

The earliest sponges are about 900 million years old.

But sponges do something great.

They slurp up a lot of detritus from the ocean.

And once the sponges did that, there was less for decay bacteria to decay.

Decay bacteria suck up all the oxygen from the seawater.

So without them...

the seawater became more oxygenated all the way down which was more space for large oxygen breathing creatures to live in to occupy another one which is related is perhaps there was more oxygen in the atmosphere which tends to happen during ice agey type times but another one which i think

is the clincher was that suddenly a lot of minerals appeared in the seawater, particularly calcium.

Now, calcium is the element from which you create bones.

Calcium carbonate invertebrates calcium phosphate.

But certainly, all mollusk shells are made of calcium carbonate.

The sugary skeletons, chitin,

of jointed-limbed creatures are reinforced with calcium carbonate.

I mean, just think of big lobsters, that sort of thing.

Now, where do all these minerals come from?

Well, it looks like there was some huge episode of continents banging into each other.

The formation of Gondwana, the great southern continent,

It seems that two large continents slammed into each other, creating the most enormous mountain range, 4,000 kilometers long at least, 1,000 kilometers wide, and who knows how high.

I mean, perhaps the greatest mountain range that ever existed on the planet.

I mean, the Himalayas today are still being created by the collision of India with Southern Asia.