Zero.

from the book "After Man: Revival"

There was nothing here once. Nothing here but a lonely old Soul.
The Soul was a sad creature. For billions of years it had lived. It had seen the creation of the galaxies and universes as we know them, and even as we don't yet know them. It had seen beings brought to life and exterminated, had seen barren planets become fruitful, had seen so many species of creatures it could no longer remember even half of the names.
But it was still so sad. Because it always had to return to Home, the place of Darkness and Shadow, the place where nothing ever happened. Anything it ever tried to bring there died long before it could explain what was going on. On this place, in this infinite space, the Soul wept.
One day, from the Soul's tears sprang a faerie. It was a darling, spindly creature, with big eyes and a heart that beat rapidly, in a soft pattern of thump thump thump that repeated every few seconds. Most importantly, the faerie was alive. And it was in Home. In shock, the Soul asked the faerie where it had come from.
'I have seen the sorrow in your heart,' said the faerie. 'I have also seen the loneliness in your soul. You ache for companionship, yet everything that comes to your Home dies. Except me.' Here, the faerie smiled at it. 'But you will be lonely no longer. You see, the Beyondlands are too full of creatures time has forgotten. They have nowhere to go, and will soon fade. But Home will make an excellent place for them, if we can work to make it fit.'
The Soul didn't need to hear more. It knew this was its chance to get what it had always wanted, so together with the faerie, it set to work. There was no day or night in Home, so it was impossible to know exactly how long it took. However, when their work ended, they had made something grand: an infinite Earth, essentially, a copy of Earth's previous and current forms, all layered into one. It would suit its purpose perfectly.
'Rest now, Soul, your work is done,' the faerie instructed the Soul as it lay its head down to sleep. 'I will bring the others from their stasis to Home. You're going to be so happy with them.'
Soul drifted off to sleep.