Chapter 14: Geologic Time How do we divide geologic time? • • • • • • • • Modern time is divided into millennia. Millennia are divided into centuries. Centuries are divided into decades. Decades are divided into years. Years are divided into months. Months are divided into weeks. Weeks are divided into days. Days are divided into hours, etc. Geological Time Scale • Geologic time covers much more time than the modern calendar. • Paleontologists have divided Earth’s history into time units based on the lifeforms that lived during certain periods. • We start with Eons, which are the longest divisions of time. • Eons are then divided into eras. • Eras are decided by worldwide changes in the types of fossils present. • For example, at the end of the Mesozoic Era many invertebrates (animals without backbones) became extinct. • Eras are then divided into periods. • Periods are marked by significant changes in the fossil record. • This can include massive expansion of life or mass extinctions. • Periods are then divided into epochs. • Smaller than periods • Characterized by differences in life forms. How does evolution relate to the divisions of the geologic time scale? Organic Evolution • The fossil record shows that species have changed over geologic time. • Environmental changes can affect an organism’s survival. • Those that don’t adapt to changes are less likely to survive. • Species: a group of organisms that normally reproduces only with other members of their group. • Offspring of 2 different species normally can not reproduce (sterile). Natural Selection • Charles Darwin proposed the theory of natural selection. – It states that organisms with characteristics that are suited to a certain environment have a better chance of surviving and reproducing than organisms that do not have these characteristics. • He sailed around the world collecting specimens and data. – He got some of his best data in the Galapagos Islands to the west of South America. Natural Selection • He saw that organisms compete with each other for resources (food and living space), and must adapt when there is not enough to go around. • He saw that organisms in the same species can show variations that could help or hurt the organism’s chance of surviving. Natural Selection Within a Species Artificial Selection • Human beings have altered the evolution of some animals by breeding only animals with desired traits. – Cats – Dogs – Horses – Cattle – Any domesticated animal • Organisms suited for their environment live longer and have a better chance of producing offspring. • Organisms poorly adapted to an environment produce few or no offspring. • A new characteristic becomes common in a species only if: – some members already possess that characteristic. – the new trait increases the animal’s chance of survival. Geologic Time Scale How do trilobites help explain evolution? • Structure of the hard outer skeleton or exoskeleton • 3 lobes that run the length of the body • Body made up of – Head-cephalon – Segmented middle-thorax – Tail-pygidium Trilobite Timescale A Variety of Trilobites AGNOSTIDA - Among the early trilobites, with a basic, clamshelllike appearance. Suborders Agnostina and Eodiscina. Representative species pictured here: Ptychagnostus akanthodes (Agnostina) REDLICHIIDA - Including the most primitive trilobites from the lower Cambrian. Suborders Olenellina and Redlichiina. Representative species pictured here: Redlichia sp. (Redlichiina) CORYNEXOCHIDA - An often spiny group united by a shared hypostomal attachment. Suborders Corynexochina, Illaenina, and Leiostegiina. Representative species pictured here: Kootenia sp. (Corynexochina) And More . . . ODONTOPLEURIDA - Very spiny trilobites, a sister group to the Lichida. Suborder Odontopleurina; superfamilies Dameselloidea and Odontopleuroidea. Representative species pictured here: Selenopeltis buchii. . LICHIDA - Some of the most ornately sculptured species fall into this group. Suborder Lichina; families Lichidae and Lichakephalidae. Representative species pictured here: Arctinurus boltoni (Lichioidea) PHACOPIDA- The well-known Phacops, with its beautiful compound eyes belongs here. Suborders Calymenina, Phacopina, and Cheirurina. Representative species pictured here: Phacops sp.(Phacopina) And more . . . PROETIDA - Includes some of the last trilobite species before the Permian Extinction. Suborder Proetina, with three Superfamilies. Representative species pictured here: Proetus granulosus (Proetoidea) ASAPHIDA - All share a ventral median suture, and most a similar development. Suborder Asaphina, with six Superfamilies comprising ~20% of all trilobites. Representative species pictured here: Homotelus sp. (Asaphoidea) PTYCHOPARIIDA - Bearing the "generic trilobite" body plan, but many weird variations! Suborders Ptychopariina and Olenina (Harpina has been elevated to order Harpetida; see below) Representative species pictured here: Modocia sp. (Ptychopariina) And would you believe, more? HARPETIDA - Bearing the distinctive, broad, often intricately pitted, cephalic fringe. In 2002, split out of the Ptychopariida and elevated from suborder to full order. Representative species pictured here: Eoharpes sp. NEKTASPIDA - The so called "soft-shelled trilobites" such as Naraoia have been classified as an order of trilobites by some. Click on the image or link to learn more about them, and to see how they are handled in the 1997 Treatise. • Trilobites lived in Earth’s oceans for more than 200 million years. • During Paleozoic Era, some species of trilobites became extinct and new ones evolved. • Trilobites showed different characteristics during the different periods of the Paleozoic Era. • Trilobite eyes changed over time and tell us about where they lived in the ocean. • Trilobite bodies-changed over time as well. How has Plate Tectonics affected species? • Earth’s moving plates caused continents to collide and separate many times. • Collisions formed mountains and trapped seas between shifting continents. • By the end of the Paleozoic Era, the separation of Pangaea caused wider and deeper seas between the continents. • Trilobites environments were changed or destroyed. • This is one theory for the extinction of trilobites.