Giant dragonflies, swamps filled with towering trees, lush plant growth in
every direction: these are the quintessential images of the paleo world and the
reality for the denizens of the Carboniferous. A warmer climate and higher
oxygen levels created this tropical world filled with large insects of frightening size: millipedes up to three feet in length,
spiders with 18-inch legs and scorpions weighing in at fifty pounds.
During this period, the advancement of Life is moving at an astonishing pace.
Amphibians lose their fish-like appearance and become more familiar to our
modern eyes. Reptiles arrived on the scene, preferring dry land to the wet
environments of their amphibious relatives. By the end of the Carboniferous,
three great lines of reptiles have emerged: the diapsids, ancestors to
dinosaurs, lizards and birds; the synapsids, ancestors to mammals; and the
anapsids, ancient ancestors of turtles.1
The new repoductive innovation of the amniote egg enabled the reptiles
to lay their eggs on land. They no longer had to rely on a
body of water in which to lay their eggs, they could be independent
of the water and lay their eggs anywhere on land, safe within a
shell, for within this
perfect little incubator, the reptile embryo need not fear starvation or
dehydration. (Even today the amphibians depend upon water to lay
their eggs, but not so for reptiles.)
As plants thrived in the tropical climate they began to produce lignin, a
bark-like substance that gave them the structural support needed to grow to
gigantic proportions. Yet lignin posed a perplexing problem for the environment.
Because it was a new substance and a very tough one at that, there were no
microbes that could consume it. The normal mechanisms of decay were thrown out
of sorts. As trees died or were toppled in storms, their trunks and branches
collected on the forest floor, the pile becoming deeper and deeper as millions
of years rolled by with no method for for breaking down the lignin. Buried by time and compressed by tectonic forces, these
layers would become the vast coal deposits that would later bring about the
industrial revolution and our modern age; thus the period acquired its name,
carboniferous, meaning ”coal bearing”.
- Oxygen reached its highest level of any age: 35% compared to modern day
measurements of 21%.
- Carbon Dioxide was the lowest in history (until modern times). The vast amounts
of vegetation pulled CO2 from the air and
it remain locked in their stalks and stems even upon death. The
microbes crucial in the process of decay were overwhelmed,
the plants did not decompose and huge amounts of CO2
remained trapped within
the plant matter. As the plants were turned into coal, the CO2 would remain
buried for eons until released in our modern age by the burning of coal.
- The supercontinent Gondwana continued to cover the South Pole; but in the first
half of the period, it collided with North America as the great supercontinent
of Pangea began to form.
- The collision of North America with Gondwana is the last
of three phases that built the Appalachian Mountains. This
mountain-building episode is called the Allegheny Orogeny.
- The oceans of Panthalassa and Paleo-Thethys were confined
within Pangea’s early circular form, but as the circle tightened
and the continents drew together these seas would slowly
- By the late Carboniferous, as the continents began to merge to form Pangea, the
marine environments disappeared, replaced by swamps and arid climates.
- The continent of Euramerica (North America and Europe) was covered in vast
swamps setting the stage for future coal deposits.
- There continued to be extensive glaciers at the South Pole.
- Warm and tropical in many regions.
- In these regions the fossilized trees lacked growth rings signifying that the climate was stable and unchanging.
- On a longer time scale the rock formations of this
period often alternate between coal and shale indicating
there was cyclic melting of glaciers that inundated dry
land producing the shale deposits. As the glaciers once
again grew and water was trapped in the ice, the land once
again dried allowing the vegetation (and the coal deposits)
- Growing areas of aridity occurred in the central areas of
- Lignin first appeared, allowing plants (especially trees) to grow strong and
tall while it inhibited decomposition.
- Most of the world’s coal deposits (especially in North
America and Europe) come from this period.
- Earliest relatives of the conifers (pine trees, etc) appeared.
- Seed-bearing plants became more sophisticated.
- The appearance of the amniotic egg freed Life from dependence on water.
- The high levels of oxygen possibly played a
considerable role in this innovation.
- Giant forms of dragonflies and other insects inhabit the land.
- One theory gaining new ground is that the high oxygen levels of the period
promoted the gigantic growth of these creatures whose respiratory system allowed
them to take advantage of higher oxygen levels.
- The high oxygen levels also played another important role: enabling the giant
insects to fly. Higher oxygen provides greater air pressures to support such
giant bodies in the air.
- Reptiles appeared. While they remained inconsequential during this time, they
diversify into three major lines: diapsid, synapsids and anapsids.
- Sharks became abundant and diversified.
- There were two minor extinctions during the Carboniferous: one in the middle of
the period and another near the end.
- Depending on the plant species, the extinction rates ranged from 40% to 85%.
- Some animal group extinctions reached as high as 70%.
- Extinctions possibly due to climate change since specific groups of
both plants and animals were impacted more than other groups.