History of Earth Timeline

1. History of Earth Timeline 4.6 bya to Present

2. The Hadean Eon From the Greek word Hades referring to the hellish conditions on early earth 4.6 bya to 4.0 bya

3. Formation of the Earth The impacts of large bodies and the decay of radioactive elements generated heat that melted the materials of the young Earth As Earth lost heat to space and slowly cooled, the materials eventually segregated into an iron core and silicate mantle.

4. Earth’s Atmosphere During the Hadean • Some believe it was mostly nitrogen • Possibly carbon dioxide, water vapor, and volcanic gases.

5. Earth’s Surface During the Hadean Few rocks have survived from the Hadean Acasta Gneiss is a metamorphic rock about 4 billion years old Acasta Gneiss implies that granitic continents and surface water existed during the Hadean

6. Earth’s Surface During the Hadean It is not known if plate tectonics operated on the early Earth One suggestion is that the earliest surface crust was thin and unstable This crust would have been recycled almost as soon as it formed

7. Plate Tectonics Layers of Earth

8. The Archean Eon 4.0 to 2.5 bya First Life Appears Plate Tectonics Established Oxygen Poor Atmosphere

9. Early Life on Earth The earliest organisms were most likely bacteria similar to today’s Archaea May have originated at deep sea vents Today’s Archaea live in sulfur springs and deep sea vents

10. Evidence of Early Life Stromatolites are made of living mats of microorganisms and thin sheets of sediment.

11. Early Continents and Oceans Silica rich plutons rise to the surface. These plutons joined together to form shields which became continental crust. Granitic crust forms the continent while basaltic crust forms the ocean floor.

12. Granite vs. Basalt Basalt Produced by oceanic-origin magmas Undersea volcanic areas represent huge spreading ridges where the earth's crust is separating Magma cools very quickly, and the minerals have very little opportunity to grow Fine grained, difficult to see individual minerals Granite Comes from magma that cools down slow enough to crystallize into solid rock. Results in a coarse-textured rock in which individual mineral grains are easily visible.

13. Changes in the Atmosphere From oxygen-poor of the Archean, into oxygen-rich in the Proterozoic Stromatolites photosynthesize and release free oxygen into the ocean Evidence of photosynthesis 2.7 bya

14. Evidence of Oxygen in the Archean Early oceans had large volumes of dissolved iron. Combined with oxygen to produce iron oxides along the continental margins. This “rust” was concentrated in sedimentary deposits known as banded iron formations. These rocks are mined worldwide for iron ore. Oxygen then began to escape into the atmosphere.

15. The Proterozoic 2.5 bya to 542 mya Earth’s Crust Forms a Platform for Life Eukaryotes and Multicellular Life Evolve Oxygen and Greenhouse Gases Increase Mountain Building and Glaciers

16. Map of the Proterozoic World

17. Complex Life Evolves The first Eukaryotes are most likely algae that evolved 2.1 to 2.6 bya. The first multicellular organisms show up in the fossil record 1.2 bya. The first multicellular animal show up at the end of the Proterozoic.

18. Mountain Building Four mountain building events with intervening erosion Converging plates created upfolding and volcanoes

19. Glaciation and “Snowball Earth” Major glaciations at the beginning and end of the Proterozoic Glaciers extend almost to the equator leading to a rock and ice covered globe

20. Global Warming Melts the Snowball Methane released from unstable ice sheets may have initiated rapid warming. More methane means more warming…leading to more melting, releasing more methane…