Geology Reference
In-Depth Information
In Chapter 8, I present a line drawing of plate boundaries. It may seem very
straightforward, with lines neatly separating continental plates from one another.
But some areas of that map are almost unknown, and the lines have been drawn
based on best-guess estimates. In regions such as the northeast Pacific plate, near
Kamchatka (a peninsula in eastern Russia), researchers today map earthquake
and volcano events in an attempt to pinpoint plate boundaries.
Mysteries of the past: Snowball earth, first life,
and mass extinctions
Later in this topic (in Chapter 16), I explain exactly how long and complex earth's his-
tory is. Many of the events in earth's history can be interpreted from patterns in rocks
that scientists observe today. The downside to a history told in rocks is that many
chapters are missing. These gaps in the record of earth's past provide fascinating topics
for further scientific exploration.
Snowball earth
A hypothesis currently being debated proposes that at some point (between approxim-
ately 600 million and 1 billion years ago) the entire planet was covered with ice. This
idea is called the
snowball earth hypothesis.
Some of the evidence to support this hypothesis includes rock formations that are the
result of massive layers of ice (glaciers, which I describe in Chapter 13) covering the
continents near the equator (at that time). Some scientists argue that an earth covered
in ice could not sustain life, and there is evidence of life in rocks from both before and
after the suggested time of the snowball. Others want to know what caused the snow
and ice to eventually melt. Another hypothesis based on the same evidence suggests
that rather than a snowball, the earth was merely a “slushball” that could have, in some
areas, still supported life during an extended, very cold period.
Will the snowball earth hypothesis fade into history as a fanciful idea? Or will it be re-
vived, perhaps proven partially true by future studies and incorporated into an accep-
ted geologic theory? Only time (and more research) will tell.
Earliest life
