The Evolution of Life

Geologic Time

The Precambrian – Age of Bacteria 4.6 billion – 545 million years ago

The Paleozoic – Age of Fishes 545-251 million years ago

The Mesozoic – Age of Dinosaurs 251-65 million years ago

The Cenozoic – Age of Mammals 65 million years ago to present day

The Precambrian – Age of Bacteria 4.6 billion – 545 million years ago

Early Microbial Evolution The earliest organisms must have been very simple resembling early prokaryotic cells. Lack nuclei Anaerobic Chemoautotrophs that obtained their carbon from carbon dioxide dissolved in the oceans.

Prokaryotes Archaebacteria - Moderen bacteria that live in extremely hostile conditions. Appear to be close to the root of the tree of life. Obtain their energy through chemical reactions. Methanogens Anaerobic Halophiles Salty conditions Thermophiles Extreme heat

Rate of Evolution in Early Organisms Early organisms experience a higher rate of evolution because… Early organisms lacked the efficient enzymes for DNA replication. There were many errors as DNA was copied from one generation to the next More errors meant more mutations and a higher rate of evolution.

What is the evidence of rapid early diversification of Organisms? Stromatolites Photosynthesis begins 3.5 billion years ago

The Oxygen Revolution 2.35 billion years ago

Photosynthesis Most important new metabolic process evolved gradually Organisms that lived close to ocean surface probably developed means of absorbing sunlight (UV in particular) Once absorbed, developed method of turning it into energy Modern organisms of purple sulfur bacteria and green sulfur bacteria much like early photosynthetic microbes, use H2S instead of H2O for photosynthesis

Photosynthesis Using water for photosynthesis developed later, perhaps 3.5 billion years ago First appearing in cyanobacteria (blue-green algae) By product of O2, released into atmosphere Changed the world!

Oxygen Crises The rise of oxygen created a crisis for life. It attack the bonds of organic molecules. Many species went extinct. Species that survived had to evolve new metabolic mechanisms or live in environments where there was no Oxygen. Oxygen could be used to generate a far superior metabolic pathway that would provide much more energy.

Early Eukaryotes Fossil evidence dates to 2.1 bill. Yr ago Dates to when O2 rising in atmosphere DNA evidence suggests that prokaryotes and eukaryotes separated from common ancestor much earlier O2 played a key role in eukaryote evolution Cells can produce energy more efficiently using aerobic metabolism than anaerobic metabolism Adaptations of aerobic organisms could develop adaptations that required more energy than would be available for anaerobic organisms

What two adaptations lead to the rise of modern eukaryotes? Some cells developed specialized infoldings of their membranes that compartmentalized certain cell functions. Large host cells absorbed smaller prokaryotes with specialized functions. These cells developed a symbiotic relationship Smaller cells developed into mitochondria

Mitochondria contain their own DNA. What evidence suggest that modern eukaryotes developed mitochondria through edosymbiosis? Mitochondria contain their own DNA. A single circular chromosome DNA is structured like prokaryote DNA Mitochondria divide independently of the cell

The Ediacaran Fauna (575 mya)

Precambrian Continents Precambrian continents were smaller, thinner, and moved more rapidly

The Paleozoic

The Paleozoic – Age of Fishes 545-251 million years ago

The Cambrian Explosion (525 mya)

The Cambrian Explosion Animal branch of the tree of life Different classifications based on body plan All known body plans made appearance in fossil record in a time span of 40 million years <1% of Earth’s age Animal diversity began 545 mill. Yr ago

Why did the diversification of animals occur so suddenly? Oxygen levels reached a high enough level for the survival of larger and more energy intensive life forms. The evolution of genetic complexity A milder climate away from a snow ball earth Efficient preditors

Why haven’t we seen other explosions of diversification like the Cambian? Once predators were efficient and widespread, it was more difficult for entirely new body forms to find an available environment.

The Cambrian World

Middle Paleozoic Seas

Dunkleosteus – Late Devonian

Colonization of Land Life flourished where liquid water exist Life on land was more complicated Had to develop means of collecting solar energy above ground and nutrients below Protection from U.V. light Life in shallow ponds or edges of lakes Water evaporates Natural selection favored that which could withstand periods of drought

Colonization of Land DNA evidence suggests that plants evolved from an algae. algae developed thick cell walls to help them survive dry periods. It took only 75 mill. Yrs for animals to follow plants out of water

Appear in the Late Silurian, diversify in the Devonian First Land Plants and Insects Appear in the Late Silurian, diversify in the Devonian

First trees and forests Late Devonian Archaeopteris

Eusthenopteron and Ichthyostega Animals move ashore Eusthenopteron and Ichthyostega

The Formation of Pangaea

Geologic Time

The Mesozoic – Age of Dinosaurs 251-65 million years ago

Origination of Mammals

Origination of Birds Archaeopteryx (Jurassic)

White Cliffs of Dover: Cretaceous Chalk

Cretaceous marine turtle, ~ 15’ Archelon Cretaceous marine turtle, ~ 15’

First Flowers, Bees, and Grass 145 million years ago in the Cretaceous period

The End-Mesozoic Extinction

Did an impact kill the dinosaurs? Iridium layer at the K-T boundary High abundance of rare metals at the K-T boundary Osmium, gold and platinum Spherical Rocks called droplets found in the K-T boundary. Soot found in the boundary.

Geologic Time

The Cenozoic – Age of Mammals 65 million years ago to present day

Radiation of mammals and large, predatory birds

The Paleogene of North America

Largest known land mammal – 18’ at the shoulder Peraceratherium Largest known land mammal – 18’ at the shoulder

Mass Extinctions

Mass Extinctions Possible Causes Impacts Active volcanism Impact sites found for K-T boundary Suspected for Permian extinction 245 mill yr ago Active volcanism Climate change External influence for copying errors Increase in solar particles or radiation hitting surface Local supernova

Extinctions Demise of Species