This is CBS I in the World. I'm John Batchewick, Tim Johnson, who is the executive editor of

The Theological magazine. Importantly, the deputy head of the School of Earth and Planetary

Sciences in Western Australia, publishing with his colleagues in Nature magazine, the

premier peer-reviewed magazine, giant impacts in the origin and evolution of continents.

We're now in the Akeian period between 3.8 and about 2.9 billion years as the period

we're looking ago. A long time ago, before what we generally understand is cellular life,

although that's a detail that'll come up. Now, the question is, is it mantle up from

the bottom or is it giant impact creating the conditions for mantle to come up? Tim has

just given us an example of the giant impact and a technical word that Tim uses in his

article, Up Welling, the mantle itself, Up Welles. When it gets to the surface, Tim,

there's an illustration in your Nature magazine of something forming on the surface. What

is that formation? Is that a craton? Is that what we're seeing now that moment?

That is the proto craton. You absolutely need that stage. That's the initial formation of this

primitive, basaltic, dark coloured proto continent. Constructed from melting the mantle, as you

said, up Welling, and up Big Up Welling of heat, much as you might see in a lava lamp,

a situation where you're having hot wax rise up. But you then need some time for that big basaltic

primitive blob to form the evolved pale coloured granites. That's so important because granites have

such a lower density compared to these basaltic primitive rocks. It's that density that basically makes

the continent float. But you have to form those granites in the first place. What we're arguing is

that it's only in the really biggest impacts that you form a big enough primitive blob that sits

there and gets hot enough at its base, that it itself starts to melt. That we know, and we've

known for a very long time from experiments and other mechanisms, that is how we produce the first

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