the mythic stories of Oz
Jack Hills and the birth of the continents
The oldest known fragments of our planet are the ~4.4 billion year old zircons from the Jack Hills some 900 km's northeast Perth. These extraordinary time capsules - crystal remnants of the very first continents - formed within a few hundred million years of the birth of the Earth and tell of an already evolved crust on the hot young Earth.
The "faint young sun paradox" relates to the fact that suns luminosity has steadily increased over the history of the Earth, from about 70% of its present value at the beginning of Earthly time 4.5 billion years ago. For our present atmosphere, temperatures would plummet to an average of -35°C if the suns radiant energy was dropped to 70% and lead to a Snowball Earth!
The Jack Hill zircons provide tantalizing evidence for the existence of water on the Earth from almost the beginning of time, and almost everywhere we look in the geological record, no matter how far back, we find evidence for a watery carapace. The early atmosphere must have been far more efficient at holding in the heat it received from the Sun, with a much greater abundance of the "greenhouse" gases (H2O, CO2 etc).
The notion that a set of feedbacks links the composition of the atmosphere to the existence of a hydrosphere provides the gist of a kind of planetary metabolism at the heart of the Gaia hypothesis. It points to a profound long-term robustness in the global system.
Geological time in millions of years (myrs)