GEOLOGIC TIME - Earth is 4.65 Ga old

• A diagrammatic representation of the last 3.8 billion years of the geological time scale of the Earth showing the different groups of organisms that evolved through time. Note that man's presence on earth represents just an extremely small fraction of the 3.8 billion year history of life on Earth. On a 24 hour clock, our species, Homo sapiens, appeared at 2 seconds before midnight.

GEOLOGIC TIME SCALE

• Geologic time terms:

Eon

Era

Period

Epoch

Age

• Two Eons:– Precambrian

(4.7 Ga - 544 Ma)

– Phanerozoic

(since 544 Ma)

• Ma = million years

• Ga = billion years

GEOLOGIC TIME SCALE• Be aware of the

Geologic Time Scale in general.

• What is the Jurassic Period?

• When did it begin? • Why is it important

to oceanography?• What is the

Pleistocene Epoch?• When did it begin

and end?

• Why is it important to oceanography?

4.65Hadean

SEDIMENT DISTRIBUTION PROCESSES(continued)

– transportation agents• ice (glaciers)

• wind (e. g., coastal sand dunes)

• Water– rivers– oceans

• waves• tides• currents• storms

– review water cycle (lesson #1)

• Roter Kamm crater, Namibia (27.7¡S 16.3¡E) Recent High altitude oblique photograph from the Space Shuttle (November 1990). One of the world's clearest craters formed by the impact of an extraterrestrial bolide stands out in this arid landscape. Note the raised rim of the crater, a common feature of both volcanic and bolide craters. This is a moderate sized impact crater, 2.5 kilometers (1.5 miles) in diameter rim to rim, and is 130 meters (400 feet) deep. However, its original floor is covered by sand deposits at least 100 m (300 ft) thick. It is thought that this crater was formed only about 5 million years ago. Because of rapid erosion on Earth, older craters are much more difficult to recognize. Many scientists believe, however, that bolide impacts have had a significant "impact" on the evolution and partial extinctions of life on earth.

• Clearwater Lakes, northwestern Quebec, Canada. Modern High altitude oblique photograph from the Space Shuttle (October-November 1985). Strongly eroded craters in Precambrian rocks of the Canadian Shield. The craters were formed by meteorite impacts dated at about 300 myBP.

• Stanley Miller's experimental apparatus for producing organic molecules from a mixture of gases believed to be similar to the Earth's primitive atmosphere.

• Chancet Cliffs, Ward Beach, NE corner of South Island, New Zealand Modern Kelp beds and tidal pools along a rocky coastline. Some scientists have proposed that life on Earth could have originated in such settings although others feel that oceanic vents are more likely sites.

• East Pacific Rise (21¡N), North Pacific Ocean. Recent. From joint US-French-Mexican RISE expedition (1979). Top of black smoker chimney in an ocean-ridge axial valley. Such sites have been proposed as the

potential environments in which life on earth began.

• Channel north of Lee Stocking Island, Exuma Islands, Bahamas. Modern. Giant stromatolites exposed showing the different growth forms on their tops and sides. The nature of the encrusting sessile plants and organisms forming the microbial mats changes throughout the year and depends on the time of their exposure. If exposed in the summer an entirely different type of plant and animal community colonizes the surface than if exposed in the colder winter months.

• Northwest Territories, Canada Precambrian, ca. 1.8 Ga Pethei Group Mid-Precambrian reef Facies: Strongly elongate stromatolites formed as part of prograding reefal rim. The domes are remarkably similar in morphology to modern forms from Shark Bay, Australia.Hammer

• Carbla Point, Shark Bay, Western Australia, Australia RecentLarge head-shaped algal/cyanobacterial stromatolites in the

upper intertidal zone of a hypersaline, tidal basin. Note elongate club shape of many of the algal heads -- this is produced by strong tidal current action. Structures similar to these are common in Precambrian rocks, indicating that this may have been what much of the

coastal world looked like for about two to three billion years.

• A diagrammatic representation of the buildup of atmospheric oxygen through geological time on Earth. Oxygen was probably generated largely though the metabolism of simple plants, mainly photosynthetic algae and/or cyanobacteria. During early history, production was consumed by the large volume of reactive, unoxidized inorganic materials at the Earth's surface. The long-term rise of oxygen was slowed and eventually balanced through animal respiration and biomass burning.