Monday November 26, 2012

1. MondayNovember 26, 2012 (Discussion and WS - The Precambrian Eon: Formation of Continents and Steps Leading to Higher Life Forms)

2. The Launch Pad Monday, 11/26/12 Which of these organisms lived during the Precambrian Eon?

3. Announcements

5. Recent Events in Science NASA, Roscosmos Assign Veteran Crew to Year-Long Space Station Mission Read All About It! www.nasa.gov/home/hqnews/2012/nov/HQ_12-406_ISS_1-Year_Crew.html The goal of their yearlong expedition aboard the orbiting laboratory is to understand better how the human body reacts and adapts to the harsh environment of space. Data from the 12-month expedition will help inform current assessments of crew performance and health and will determine better and validate countermeasures to reduce the risks associated with future exploration as NASA plans for missions around the moon, an asteroid and ultimately Mars.  NASA, the Russian Federal Space Agency (Roscosmos), and their international partners have selected two veteran spacefarers for a one-year mission aboard the International Space Station in 2015. This mission will include collecting scientific data important to future human exploration of our solar system. NASA has selected Scott Kelly and Roscosmos has chosen Mikhail Kornienko. Kelly and Kornienko will launch aboard a Russian Soyuz spacecraft from the BaikonurCosmodrome in Kazakhstan in spring 2015 and will land in Kazakhstan in spring 2016.

6. The Precambrian Eon The Precambrian Eon is the large span of time in Earth's history before the current Phanerozoic Eon, and is further divided into the Archaen and the Proterozoic Eons. The Precambrian begins with the formation of Earth about 4570 Ma (million years) ago, and ends with the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance. The Precambrian accounts for 88% of geologic time.

7. The Precambrian Eon Not much is known about the Precambrian, despite its making up roughly seven-eighths of the Earth's history, and what little is known has largely been discovered in the past 50 years. The Precambrian fossil record is poor, and those fossils present (e.g. stromatolites ) are of limited biostratigraphic use. This is because many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.

8. Figure 11.19 The Precambrian Eon

9. The Precambrian Eon Much of Earth’s stable continental crust was created during the Precambrian. Partial melting of the mantle formed volcanic island arcs and ocean plateaus.

10. The Precambrian Eon These crustal fragments collided and accreted to form larger crustal provinces. Larger crustal areas were assembled into larger blocks called cratons. Cratons form the core of modern continents.

11. Formation of Continental Crust According to one model, the growth of large continental masses were accomplished through the collision and accretion of various types of terrains, including volcanic arcs and oceanic plateaus.

12. The Extent of Crustal Materials Remaining From the Archean and Proterozoic Eons

13. Map showing the major geological provinces of North America and their ages in billions of years (Ga). It appears that North America was assembled from crustal blocks that were joined by processes very similar to modern plate tectonics. These ancient collisions produced mountainous belts that include remnant island arcs trapped by colliding continental fragments.

14. The Precambrian Eon The Supercontinents The supercontinents were large landmasses that consisted of all, or nearly all, of the existing continents. Pangaea was the most recent supercontinent, but perhaps an even larger one, Rodinia, preceded it. Splitting and reassembling of supercontinents have generated most of Earth’s major mountain belts. Supercontinents have also profoundly affected Earth’s climate over time.

15. Possible Configuration of the Supercontinent Rodinia Figure 12.15

16. The Precambrian Eon It was during the Precambrian Eon that life first began on the Earth. Although the Precambrian Eon contains some 88% of Earth's history, its fossil record is poor because organism were soft-bodied during this time, resulting in little remaining evidence.

17. The Precambrian Eon The majority of Precambrian fossils are stromatolites that are often heavily metamorphosed or deeply buried. However, preserved cells have been discovered at selective sites, such as the 2.0 Bya Gunflint Formation Jasper stromatolites from Gunflint Formation near Mackies, northern Ontario.

18. The Precambrian Eon The earliest life forms were prokaryotes that evolved in the seas, possibly as early as 3.8 Ga. • The first primitive prokaryotic single-celled organisms appeared in the oceans in the form of bacteria (eubacteria or Achaea).

19. The Precambrian Eon Earth’s first living organisms were probably chemotrophs existing in an anoxic world and producing H2S or CO2.

20. The Precambrian Eon Nearly 3.5 Ga, photosynthezing cyanobacteria began releasing oxygen into the atmosphere as a by-product of the process of photosynthesis.

21. The Precambrian Eon The first multi-cellular organisms appeared toward the end of the Precambrian Eon, sometime prior to 542 Ma.

22. The Precambrian Eon When the eukaryotes (single-celled organisms with a nucleus) evolved through endosymbiosis is disputed, with claims as early as 3.4 Ga, but with less equivocal fossils dating from 1.8 to 0.8 Ga.

23. The Precambrian Eon With the eukaryotes comes sexual reproduction, enabling genetic diversity and the concomitant ability to adapt to and survive environmental changes.

24. Worksheet The Precambrian Eon: Formation of Continents and Steps Leading to Higher Life Forms