The History of Life Ch. 17

Fossils and Ancient Life Paleontologist are scientists who study fossils. Fossil Record provides evidence about the history of life on Earth . It also shows how different groups of organisms, including species, have changed over time. More than 99% of all species that have ever lived on Earth have become extinct.

How Fossils Form Most fossils form in sedimentary rock. Sedimentary rock is formed from small particles of sand, silt, and clay. Soft parts of organisms are typically not preserved but hard parts like bones or wood are.

Things that can form fossils Eggs Footprints Body Parts

Fossil Evidence Relative dating – use of Carbon Dating can provide a relative age for a fossil. Relative dating allows paleontologist to estimate a fossil’s age compared with that of other fossils. Index Fossils – organisms that must have existed for a short period over a wide geographic range. Half-Life – length of time required for half of the radioactive atoms in a sample to decay

Geologic Time Scale The basic divisions of time from larger to smaller is eras and periods.

Eras Precambrian – Characterized by small multicellular life forms Paleozoic – diversity of marine life Meozoic – marked by appearance of flowering plant life Cenozoic – mammals become predominant life forms. Most recent Era

Paleozoic Era Major Point: Cambrian Explosion – the massive diversification of life during the early Cambrian Period Major Mass Extinction: The mass extinction at the end of the Paleozoic Era affected both plants and animals on land and in the seas. As much as 95% of the complex life in the oceans disappeared. Ex. Trilobites and many amphibians became extinct.

Mesozoic Era Major Characteristic: This is when dinosaurs became the predominate life forms and when flowering plants appeared.

MacroEvolution

Macroevolution Extinction Adaptive radiation Convergent evolution Coevolution Punctuated equilibrium Changes in developmental genes

Extinction Mass extinctions made rapid evolution of surviving species possible because it made new habitats available to them.

Adaptive Radiation One common ancestor. Different environmental stressors (needs) encourage the success of organisms with specific traits.

Convergent Evolution Different ancestors SAME environmental stressors. Causes different species to have similar physical traits.

Coevolution Two species that interact closely together change over time so that both species benefit the most.

Punctuated Equilibrium Common ancestor but sudden changes in each organism.

Changes in Developmental Genes Over time, changes in genes cause organisms to look much different than their ancestors.

Punctuated Equilibrium Convergent Evolution Coevolution Adaptive Radiation