Name ______________________________ Seat # ______ Date ___________________ Period ______

Earth SciencePanama Isthmus

ObjectiveI will use various different graphics, answer questions about the graphics in order to write a 20 word or less answer to the driving question, “when was the Atlantic and Pacific Ocean separated by land?”

Driving Question: When was the Atlantic and Pacific Ocean separated by land?

Background InformationAn isthmus is a narrow strip of land, bordered on both sides by water that connects two larger pieces of land. Panama is an example of an isthmus.

Analysis You will need to read, look at the graphics and answer the questions next to the graphics.Weather Patterns Affect SalinityAlthough separated by a thin isthmus of land, the Caribbean Sea and the Pacific Ocean have significant differences in ocean chemistry and climate. Examine the two images to see the differences in temperature and salinity. Salinity is defined as being the saltiness of the ocean.

1. Fill in the blanks below using the following bodies of water:

Atlantic OceanPacific OceanCaribbean Sea

A. Saltiest: ________________________

B. Medium saltiest: _________________

C. Least saltiest: ___________________

2. What are the temperatures of the following bodies of water?

A. Atlantic Ocean: ___________________

B. Pacific Ocean: ____________________

C. Caribbean Sea: ___________________

Name ______________________________ Seat # ______ Date ___________________ Period ______

3. Based on the diagram, why is the Caribbean and Atlantic Ocean saltier then the Pacific Ocean?

Variations in Salinity and Oxygen IsotopesYou know that water is made of hydrogen and oxygen atoms arranged in molecules of H2O, but you

may not be aware that there are different types of oxygen atoms. Different atoms of the same element are called isotopes. All oxygen atoms have 16 protons and 16 electrons, but some oxygen atoms have 16, 17, or 18 neutrons in the nucleus. The most abundant isotopes of oxygen in seawater are oxygen sixteen (16O) and oxygen eighteen (18O).

Water molecules with 16O atoms evaporate more easily than water molecules with 18O atoms, so the relative numbers of 16O and 18O atoms that remain in the water change as evaporation occurs. Water from which 16O atoms have preferentially evaporated has a higher ratio of 18O to 16O atoms than water that has experienced less evaporation. As salinity also increases as evaporation occurs, we can generalize the relationship to state that water with an increased 18O to 16O ratio is saltier than water with a lower 18O to 16O ratio.

4. Which oxygen isotope evaporates quicker, 18O or 16O? __________

5. Which oxygen isotope results in a saltier ocean, 18O or 16O? __________

Name ______________________________ Seat # ______ Date ___________________ Period ______What microfossils reveal about ocean chemistry

Microfossils are the remains of microscopic ocean organisms. These organisms built their shells from chemicals present in seawater while they were alive. Oxygen atoms got locked into the shells as they were built. Scientists analyze the ratio of 18O to 16O atoms in the shells of microfossils to deduce the salinity level that existed at the time the organisms were living. Scientists can track changes in salinity by observing changes in oxygen isotope ratios in shells that formed at different times.

To find shells that formed at different times, geologists drill into the ocean floor and bring layers of sediments to the surface encased in tubes. These are called cores. Sedimentologists and paleontologists observe samples from the cores under high-powered microscopes to detect microfossils. The deeper the microfossils are found, the older they are.

6. What are microfossils? ___________________________________________________

7. How do scientists track salinity levels in the ocean? ____________________________

8. What is a core? ________________________________________________________

Identifying Microfossils in Caribbean and Pacific CoreYou've seen how isotopes in microfossils indicate changes in ocean chemistry over time. Now

you'll look at another piece of evidence from microfossils.Layers of sediments from as far back as six million years ago have been extracted from drilling

sites in both the Caribbean and the Pacific. The inset images show fossils of microorganisms called foraminifera. This species of foraminifera has been found in sediment cores from drilling sites on both sides of the Isthmus.

9. How do you think this marine species could have spread to both sides of the isthmus?

Name ______________________________ Seat # ______ Date ___________________ Period ______Pulleniatina as an Indicator of ChangeThe image below shows another kind of foraminifera called Pulleniatina. Unlike other microfossils, Pulleniatina is not found on both sides of the isthmus through time. In the graphic below, you’ll determine which layers have Pulleniatina fossils.

Pacific and Caribbean Drill Site Pictures *You will need to get these from the teacher and use it to answer question #10.

10. Identify in which layers Pulleniatina was present by writing present or not present in the line provided

Pacific Drill Site Layers

Layer 6: ___________

Layer 5: ___________

Layer 4: ___________

Layer 3: ___________

Layer 2: ___________

Layer 1: ___________

Caribbean Drill Site Layers

Layer 6: ___________

Layer 5: ___________

Layer 4: ___________

Layer 3: ___________

Layer 2: ___________

Layer 1: __________

11. How would you explain the presence or absence of Pulleniatina only on the Pacific Ocean side?

_____________________________________________________________________________

Dating the Formation of the Isthmus of Panama

By examining the collections of microfossils, you can see that Pulleniatina is present in sediments only on the Pacific side and only in the more recent layers of sediments. Pulleniatina is an example of an organism that had been isolated from other groups of foraminifera, then diverged to become an entirely new species.

At some stage in Earth's geological history, a land bridge formed, connecting Central and South America and closing off the Caribbean Sea from the Pacific Ocean. Pulleniatina was a species that developed in the new conditions of the Pacific Ocean. It did not have an opportunity to spread to the Caribbean side because the land bridge was in the way.

Answer the driving questionBased on what you read, the graphics you looked at and the questions you answered now you are ready to answer the driving question. *REMEMBER YOU HAVE TO USE 20 WORDS OR LESS IN YOUR ANSWER.

12. When was the Atlantic and Pacific Ocean separated by land?

___________________________________________________________________________________

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