Geology of British Columbia Part 2

FROM THE HADES TO THE ARCHEAN

In the first part in June, we discussed the very earliest geological history of British Columbia. Now we will advance beyond the

Hadean, because we have still got four billion years to cover. Believe it or not, evidence of life as old as four

billion years has been found, about the time the first continents had formed and stabilized.

So now we move from "Hades" to the "third" day of creation, the Archean. This covers an enormous period

of time from four billion years ago to two and a half billion years ago. The oldest rock in existence that we

have is the Acasta Gneiss from four billion years ago collected in the Northwest Territories. My Masters

Thesis in Geophysics in 1966 discussed the evolution of North America long ago and formation of a

protocontinent 4070 million years ago with the greenstone belts as a remnant. It was not well received. But

eventually it had to be accepted because it was the most logical explanation of the evidence.

Archean rocks are distinguished by the presence of heavily metamorphosed deep-water sediments, such as

mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations,

consisting of alternating high- and low-grade metamorphic rocks. (rocks altered by heat and pressure). The

high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent

deep-sea sediments eroded from the neighboring island rocks and deposited in an adjacent basin. In short,

greenstone belts are all that's left of former land masses.

The picture is a photo I took of a remnant of earliest life I took in 1966. It shows a fossilized stromatolite

growing on a lava flow of basalt. Stromatolites are layered, rock-like structures built by ancient, microscopic

organisms (cyanobacteria). As the most ancient fossilized evidence of life on Earth, they date back over 3.5

billion years. By photosynthesizing, these cyanobacteria helped create Earth's early oxygen atmosphere.

As you would expect these ancient creatures still exist in Australia. Here is a photo of one as it exists today.