terrestrial fossil records and paleogeography

TERRESTRIAL FOSSIL RECORDS AND PALEOBIOGEOGRAPHY

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What are fossils?

Are the preserved remnants or impressions left by organisms that lived in the past

best places to find them are in lake, swamp and river deposits.

In essence, they are the historical documents of biology

Fossils

FOSSIL RECORDS

The fossil record is the ordered array in which fossils appear within sedimentary rocksThese rocks record the passing of geological time

Sedimentary rocks are the richest source of fossils

Sedimentary rocks are form from layers of sand and silt that settle to the bottom of seas and swamps

As deposits pile up, they compress older sediment below them into rockThe bodies of dead organisms settle along with the sediments, but only a tiny fraction are preserved as fossils Rates of sedimentation vary depending on a variety of processes, leading to the formation of sedimentary rock in strata

The oldest fossils are usually in the deepest layers of sedimentary rocks

Types of Terrestrial Fossils

• Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

• Trace fossils record the activity of an organism

• Index fossils can provide the relative age of a rock layer. – existed only during

specific spans of time– occurred in large

geographic areas• Index fossils include

fusulinids and trilobites.

Index fossils are another tool to determine the age of rock layers.

Permineralization occurs when minerals carried by water are deposited around a hard structure.

Fossils can form in several ways:

A natural cast forms when flowing water removes all of the original tissue, leaving an impression

• Preserved remains form when an entire organism becomes encased in material such as ice.

• Specific conditions are needed for fossilization.

• Only a tiny percentage of living things became fossils.

• Specific conditions are needed for fossilization.

• Only a tiny percentage of living things became fossils.

Determining the age of Fossils

• Radiometric dating uses decay of unstable isotopes.– Isotopes are atoms of an element that differ in their

number of neutrons.

neutrons protrons

Radiometric dating provides an accurate way to estimate the age of fossils.

Radiometric dating uses decay of unstable isotopes.

– Isotopes are atoms of an element that differ in their number of neutrons.

– A half-life is the amount of time it takes for half of the isotope to decay.

newly formed rock

parent isotope

daughter isotope

Fig. 17-11, p. 268

Stepped Art

after one half-life

after two half-lives

• Relative dating estimates the time during which an organism lived.– It compares the

placementof fossils in layers of rock.

– Scientists infer the order inwhich species existed.

Fossils, evolution and BiogeographyBiogeographyGeologic time scale

Darwinian Model

Actual Data

Appearance of complex creatures

Created after their kind

Tree of life Cambrian

PrecambrianTime

Examining the Evidence

Biogeography

-attempts to explain why species and higher taxa are distributed as they are, and why the diversity and taxonomiccomposition of the biota vary from one region to another

An example of Biogeographical Map

Geographic spread of organisms also tells of their past evolution.

MARSUPIAL EXAMPLE

AREA CLADOGRAMS

?

Fossil evidence shows that marsupials evolved in the Jurassic but after the continents started to break-up, the marsupials must have got separated into two populations, one in the Americas and the other in Australasia. In fact fossil marsupials have even been found in Antarctica and South Africa as well, providing evidence that that these continents acted as a land bridge connecting the two populations for a time.

CONGRUENT BIOGEOGRAPHIES(Comparative Phylogeography)

KEY CONCEPT The geologic time scale divides Earth’s history based on major past events.

• The history of Earth is represented in the geologic time scale.

• Cumulative findings from biogeography, comparative morphology, and geology led to new ways of thinking about the natural world

100250

550

1000

2000

PRECAMBRIAN TIME

Cyanobacteria

This time span makes up the vast majority of Earth’s history. It includes the oldest known rocks and fossils, the origin of eukaryotes, and the oldest animal fossils.

• Eras last tens to hundreds of millions of years.– consist of two or more periods– three eras: Cenozoic, Mesozoic, Paleozoic

• Periods last tens of millions of years.– most commonly used units of time on time scale– associated with rock systems.

• Epochs last several million years.

CambrianPrecambrian

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