Geology Reference
In-Depth Information
tinents are now clustering together, and gone is the lush vegetation on land, for
now only a thin smearing of microbial crusts and mats covers the rocks. Plunging
into the shallow sea at the edge of the continent you see a host of armoured
trilobites, sea scorpions and strange spiralarmed starfish. Sponges sift the nutri-
tious seawater, and microscopic silica-shelled radiolarians hunt for phytoplank-
ton prey by extending their bulging pseudopods into the light-filled sea.
You take your leave of this almost familiar world, and plunge deeper and deeper
into time, falling now like a slowly twirling autumn leaf for much longer than
before, until you reach 1,800 million years ago. The smaller continents are still
covered with rock-dissolving bacterial mats, and there are large red deposits on
the land, indicating that free oxygen is still present in the air. Diving into the
shallow seas on the continental shelves, at first you see no life at all. Shrinking
yourself down to the size of a full stop, and then one thousand times smaller still,
you encounter a multitude of tiny single-celled beings, each containing a spheric-
al globule, the nucleus, which holds their genetic material. You also see a host of
even tinier sausage- and corkscrewshaped beings—the bacteria.
Staying small, you plunge down even further to 3,500 million years ago. Seen from
space, Gaia is no longer a blue jewel, for now there is precious little oxygen in
the atmosphere. The sea is greenish, reflecting a pinkish methane-dominated sky.
Gone are the abundant continents; you see only a smattering of volcanic islands
dotted about in the sea, into which you fall like the tiniest mote of dust. There in
the upper sunlit reaches of the water you spy only bacteria—gone are the larger
nucleated beings of the earlier world. Some of the bacteria are green, and exude
small bubbles of gas—oxygen—which is quickly gobbled up by oxygen-hungry
iron and sulphur compounds. Large bacterial colonies, the stromatolites, secrete
their chalky domes wherever the waters are shallow enough to support them.
Now you fall into the deepest recesses of time, until you reach 4,600 million years
ago, long before Gaia existed, when the Earth was a newly formed ball of rock.
Floating in space, you see huge comets and meteorites bombarding the nascent
planet, provisioning it with water and other key ingredients for her future as the
mother of life. Astonished, you watch as a massive planet the size of nearby Mars
crashes into the Earth, melting both partners and sending shards of molten rocky
debris into orbit that eventually coalesce into the moon.
