High-Bandwidth Version
Search Evolution  
Click to return to the Evolution Home Page
darwin change extinction survival sex humans religion
Deep Time

Intro | Precambrian Eon | Paleozoic Era | Mesozoic Era | Cenozoic Era

Paleozoic Era: (543-248 mya)

Cambrian | Ordovician | Silurian | Devonian | Carboniferous | Permian



Silurian Period (443-417 mya)

Following the sharp cooling at the end of the Ordovician period, the climate warms in the Silurian and remains relatively stable throughout. Melting glaciers prompt global sea levels to rise, thereby creating new marine habitats. Of note, corals begin to build extensive reef formations. While some shallow-water marine animals now inhabit deeper waters, others venture into freshwater habitats and onto land. As the jawless fishes continue to thrive, early jawed fishes, including the sharklike acanthodians and the armor-headed placoderms, evolve.

Land areas comprise the fragmented remains of Rodinia supercontinent, primarily Gondwana in the southern hemisphere, and Laurentia, Baltica, and Siberia near the equator. While low-lying green algae had earlier pioneered land for the plant kingdom, more complex vascular plants now begin to grow upright. Arthropods are the first animals to join plants on land.

425 mya: Vascular land plants

Early vascular land plants -- so named for internal veinlike tubes that circulate water and nutrients -- send shoots skyward to capture sunlight and release reproductive spores to the winds. Most grow only a few centimeters tall. With deeper root systems than earlier plants and a rigid stem to support upright posture, they are now equipped to colonize more of Earth's surface.

425 mya: Great mountain ranges form

Extensive mountain ranges form when two of Rodinia's former land blocks, Laurentia and Baltica, collide. The crust in the collision zones buckles, and the rocky formations that result comprise the earliest parts of the Appalachian mountain range, as well as corresponding mountain belts in present-day Greenland, Scotland, Ireland, and Norway.

420 mya: Arthropods on land

Arthropods are the first animals to adapt to land. In most ways, they were pre-adapted to life on land. By the time they move ashore, they have already evolved an ultralight body and spindly but strong legs to counteract the force of gravity. Their hard outer shells, called cuticles, provide protection and retain moisture. Spiders, centipedes, and mites are among the earliest land variants.

-> Go to the Devonian Period

Intro | Precambrian Eon | Paleozoic Era | Mesozoic Era | Cenozoic Era

  related web activities  
Origins of Humankind
See the humanlike species that came before us.
A Modern Mass Extinction?
Are we in the midst of one? And if so, did we trigger it?
Life's Grand Design
Are nature's complex forms evidence of "intelligent design?"
  related topics  
  Deep Time/History of Life  
  Evolution of Diversity  
  Evidence for Evolution  
Videos Web Activities Site Guide About the Project FAQ Glossary Site Map Feedback Help Shop