Geologic Time and Evolution

1. Geologic Time and Evolution

2. Earth Has a History • Geologic materials record enormous changes. • Earth is a complex, evolving system. • Physical and biological systems continuously interact. • Earth constantly changes and has done so through time. • Species arise, flourish and disappear forever. • Continents rift, drift and collide. • Ocean basins open and close. • Sea-level rises and falls.

3. The Hadean Eon • Earth was inhospitable; a molten surface. • Evidence of solidified igneous rock dates from 4.4 billion years. • This evidence is from zircon grains, not a whole rock.

4. The Hadean Eon • Volcanic outgassing created a deadly atmosphere. • N2, NH3, CH4, H2O, CO, CO2 and SO42- were components. • This atmosphere had a greater density that today’s. • Early formed crust was bombarded by meteorites. • Meteorite impacts were abundant between 4.0 and 3.9 billion years. • This would have destroyed early formed crust. • Oldest evidence of crust is 4.03 billion years.

5. The Hadean Eon • The first oceans formed as rain from the skies. • Liquid water required cooling of the surface. • First evidence of oceans from marine sediments ~ 3.85 Ga.

6. The Archean Eon • Time of significant change to planet Earth. • ~3.8 billion years, Earth had cooled to form a crust. • Intense meteorite bombardment ceased. • Portions of the rock record begin to survive.

7. The Archean Eon • Life first appeared during the Archean. Evidence? • Biomarker molecules. • Isotopic signatures. • Preserved fossil cells. • Clear evidence of life in rocks dated to 3.5 billion years. • Life may have started earlier. • Oldest undisputed bacteria fossils ~ 3.2 billion years.

8. The Archean Eon • Rocks after 3.2 Ga contain stromatolites. • Layered mats of cyanobacteria (blue-green algae). • Sediments stuck to mucous coatings on algal filaments. • Photosynthesis changed Earth’s atmosphere. • Converts CO2 and H2O to organic matter and free oxygen.

9. The Proterozoic Eon • Protero = first; zoic = life. • Named before Archean life was discovered. • ~ 2 Ga (2.5 to 0.542 Ga); almost ½ of Earth history. • The unfamiliar Archean world changed to… • Fewer, larger lithospheric plates. • Larger continental landmasses. • An oxygenated atmosphere.

10. The Proterozoic Eon • Atmospheric O2 permitted diversification of life. • Aerobic respiration more efficient; allowed multicellular life. • Without O2, only single celled organisms possible. • Eukaryotic (nucleated) cells evolved by at least 1.0 Ga. • The possibility of a land-dwelling biota. • O2 made formation of the ozone layer possible. • Ozone absorbs deadly ultraviolet (UV) radiation. • Prior to the ozone layer, exposed land was bathed in UV.

11. The Proterozoic Eon • Over the last 500 Ma of the Proterozoic… • A gigantic leap in biological complexity. • Simple organisms gave way to complex ones. • Ediacaran fauna – Unusual soft-bodied fossils. • Preserved in end Proterozoic sediments. • Multicellular invertebrates resembling worms and jellyfish.

12. The Phanerozoic Eon • Phaneros = visible; zoic = life. • The most recent 542 Ma of Earth history. • Began with appearance of diverse hard-shelled organisms. • Hard-shells vastly increased fossil preservation. • Made possible a more complete archive of life on Earth.

13. The Phanerozoic Eon • The Phanerozoic is divided into 3 Eras. • Paleozoic – Ancient life. • Mesozoic – Middle life. • Cenozoic – Recent life. • Eras emphasize changes in Earth’s biota.

14. The Early Paleozoic • Cambrian and Ordovician Life Evolution: • Earliest Cambrian – Hard shells appeared for the 1st time. • Massive diversification followed: the “Cambrian explosion.” • Reflects the evolution of a complex ecosystem. • Plankton, deposit feeders, giant predators.

15. The Early Paleozoic • Cambrian and Ordovician Life Evolution: • Life during the Ordovician included several “firsts.” • The 1st vertebrates were jawless fish (agnathans). • The 1st crinoids (flower-like echinoderms). • The 1st green algae and primitive land plants. • The end of the Ordovician witnessed a mass extinction. • The seas roiled with life, but there was no life on land yet.

16. The Middle Paleozoic • Silurian and Devonian Life Evolution: • New species replaced those lost to extinction. • Vascular land plants evolved and spread across Earth. • Internal water transport systems. • Woody tissues. • Seeds. • Land plants changed Earth.

17. The Middle Paleozoic • Silurian and Devonian Life Evolution: • Fish rapidly evolve and proliferate. • Jawed fish. • Boney fish. • The 1st land animals followed plants. • Scorpions. • Spiders. • Insects. • Crustaceans.

18. The Middle Paleozoic • Silurian and Devonian Life Evolution: • At the end Devonian, the 1st amphibians appeared. • Walked on legs. • Breathed air with lungs.

19. The Late Paleozoic • Carboniferous and Permian Life Evolution: • Life continued to evolve. • Dense tropical wetlands hosted vegetation and giant insects. • Amphibians diversified. • Reptiles appeared for the 1st time. • The amniote egg permitted reproduction away from water. • Reptiles populated previously inhospitable environments.

20. The Late Paleozoic • Carboniferous and Permian Life Evolution: • The Paleozoic ended with the Permian extinction. • 90% of all marine species disappeared. • Some evidence links the extinction to a bolide impact.

21. Early and Mid-Mesozoic Era • Triassic and Jurassic Life Evolution: • New species filled niches vacated by extinction. • Corals became dominant reef builders. • Gymnosperms proliferated. • Reptiles diversified. • Plesiosaurs – Swimming reptiles. • Pterosaurs – Flying reptiles. • Turtles appear.

22. Early and Mid-Mesozoic Era • Triassic and Jurassic Life Evolution: • By end of the Triassic the first true at dinosaurs appeared. • Dinosaurs differ from other reptiles in significant ways. • Legs are positioned beneath their bodies. • They bear evidence of warm bloodedness. • By the end Jurassic giant sauropods were abundant.

23. Early and Mid-Mesozoic Era • Triassic and Jurassic Life Evolution: • The 1st feathered birds (archaeopteryx). • The 1st ancestors of mammals appeared at Triassic. • They resembled small rat like creatures.

24. The Late Mesozoic • Cretaceous Life Evolution: • Teleost fish appeared and became dominant. • Symmetrical tails, specialized fins, short jaws, rounded scales. • Swimming reptiles and gigantic turtles swam the seas. • Angiosperms (flowering plants) appeared and spread. • Produce seeds rapidly. • Insects facilitate pollination. • Hardwood trees proliferated.

25. The Late Mesozoic • Cretaceous Life Evolution: • Dinosaurs reached their evolutionary peak. • Inhabited almost all environments on earth. • Social herds of grazing dinosaurs roamed the plains. • Large carnivores fed upon the herbivores. • Pterosaurs soared overhead, birds began to diversify. • Mammals developed larger brains and specialized teeth.

26. The Late Mesozoic • The K-T (Cretaceous–Tertiary) boundary event. • There is abundant evidence of catastrophic change. • Instantaneous global change in fossil assemblages. • Sudden mass extinction of most species on earth. • The dinosaurs which had ruled the planet for 150 Ma vanished. • 90 percent of plankton disappeared. • 75% of plant species vanished.

27. The Late Mesozoic • The K-T (Cretaceous–Tertiary) boundary event. • Catastrophic impact by a 10 km comet or meteorite. • The Chicxulub crater lies beneath the northern Yucatan. • Radiometric dating indicates the crater formed at ~ 65 million years. • 100 km wide; 16 km deep. • Periodic impacts are likely contributors to other extinctions.

28. The Cenozoic Era • Cenozoic (65 Ma-present) – The most recent history. • Cenozoic Paleogeography: • During the last 65 million years, Earth has continued to change. • The final stages of the breakup of Pangaea. • Australia detached from Antarctica. • Greenland separated from North America • The North Sea formed between Britain and Europe. • Sea-floor spreading continued to open the Atlantic Ocean.

29. The Cenozoic Era • Cenozoic Life Evolution: • After the K-T boundary, plant life recovered. • Forests of angiosperms and gymnosperms reappeared. • The 1st grasses appeared in the middle Cenozoic. • Dinosaur descendants (birds) diversified and spread.

30. The Cenozoic Era • Cenozoic Life Evolution: • The Cenozoic is known as the age of mammals. • Mammals rapidly diversified to fill vacated niches. • By mid-Cenozoic huge mammals appeared. • Woolly mammoths. • Giant beavers. • Ground sloths. • Late Cenozoic, human ancestors 1st appeared.

31. The Cenozoic Era • Cenozoic Life Evolution: • Ape-like primates diversified in the Miocene (~ 20 million years). • The 1st human-like primate appeared about 4 million years. • The first members of the genus Homo appeared to 2.4 million years.

32. The Cenozoic Era • Cenozoic Life Evolution: • What sparked the evolution of the genus Homo? • Climate changes that led to the spread of grasslands? • Permitted departure from the trees. • Life on the ground allowed more time for infant development. • This permitted growth of larger brains. • Homo erectus appeared ~ 1.6 million years. • Made stone axes. • Homo sapiens appeared ~ 500 thousand years. • Modern humans appeared ~150 thousand years. • Many giant mammals died off 10 thousand years. • Climatic change? • Hunting pressure by humans?

33. The Geologic Time Scale

34. Pangea • Comes from Latin words • Pan = whole • Gaia = Mother Earth • Proposed by German scientist Alfred Wegener • Idea was based on: • “Fit” of the continents. • Location of glaciations. • Fossil evidence. • Rock type and structural similarities. • Paleoclimatic evidence.

35. Pangea

36. Glacial Evidence

37. Paleoclimatic Evidence

38. Fossil Evidence • Identical fossils found on widely separated land. • Mesosaurus – A freshwater reptile. • Glossopteris – Subpolar plant with heavy seeds. • Lystrosaurus – A non-swimming, land-dwelling reptile. • Cynognathus – A non-swimming, land-dwelling reptile.

39. Geologic Time • Discovering the magnitude of the Earth’s past was a momentous discovery in the history of humanity. • This discovery forever altered our perception of ourselves within nature and the Universe.

40. Geologic Time • Before the lat 17th century, geologic time was thought to be the same as historical time • Believed Earth formed on October 23, 4004 BCE • Scientists began to find clues to an ancient Earth • Observed marine fossils high in the mountains • Ancient animals in loose sediment • Suggested long periods of time

41. Geologic Time • There are two ways of dating geological materials. • Relative ages – Based upon order of formation. • Qualitative method developed 100s of years ago. • Permit determination of older vs. younger relationships. • Numerical ages – Actual number of years since an event. • Quantitative method developed recently. • Age is given a number.

42. Relative vs. Absolute • Relative ages assign order to events. • Numerical ages assign exact dates to events.

43. Relative Age • Uniformitarianism – The present is key to the past. • Physical processes that we observe today operated in the same way in the geological past. • Modern processes help us understand ancient events.

44. Relative Age • Superposition. • In an undeformed sequence of layered rocks… • Each bed is older than the one above and… • Younger than the one below. • Younger strata are on top; older strata below.

45. Relative Age • Horizontality and continuity. • Strata often form laterally extensive horizontal sheets. • Subsequent erosion dissects once-continuous layers. • Flat-lying rock layers are unlikely to have been disturbed.

46. Relative Age • Crosscutting relations • Geologic features intrude on preexisting strata • Igneous intrusions (dikes and sills) • Faults • Plutons

48. Relative Age • Inclusions – A rock fragment within another. • Igneous xenoliths – Country rock that fell into magma. • Weathering rubble – Debris from pre-existing rocks. • The inclusion is older than the material enclosing it.

49. Relative Age • Fossil (faunal) succession • Fossil remnants, or traces of once living organisms, are often preserved in sedimentary rocks. • Fossil are useful for relative age determination. • Several types of fossils will occur as an assemblage. • Fossils are time markers.

50. Fossil Succession • Species evolve, exist for a time, and then go extinct. • First appearance, range, and extinction dates rocks. • Fossils succeed one another in a known order. • A time period is recognized by its fossil content.