The Environment and change over time Chapter 6

The Fossil Record Fossils are perserved remains or evidence of once living organisms. All the fossils ever discovered on Earth make up the fossil record. Fossils help scientists figure out what species that no longer exist looked like when they were alive.

Fossil Formation Most fossils are formed of the hard parts of an organism. Sometimes when the remains of an organism get buried in mud, wet sand, or sediment under a body af water, the molecules that formed the remains get replaced by minerals in the water. This is called mineralization. In carbonization, a fossil formed when a dead organism is compressed over time and pressure drives off the organisms liquids and gases. Sometimes organisms leave an impression in sand or mud.

Determining a Fossil’s age Scientists cannot date most fossils directly. Instead they usually find the age of the rocks around the fossil. In relative age dating, scientists determine the relative order in which rock layers were deposited. In an undisturbed rock formation, the older layers of rock are below the younger layers of rock. Relative age dating has helped scientists figure out the order that species have appeared on Earth. Absolute age dating is more precise. It invovles radioactive isotopes that decay to become stable isotopes over time.

Fossils over time The geologic time scale is a chart that divides Earth’s history into different time units. Earth’s history is divided into Eons. Earth’s most recent Eon- The Phanerozoic Eon- Is subdivided into three parts.

Extinction When the last individual organism of a species dies, an extinction has occurred. A mass extinction occurs when many species die off within a few million years or less. The fossil record shows evidence of five mass extinctions during the Phanerozoic eon. Extinction can occur if the environment changes quickly, for example- as the result of a meteorite impact. Extinctions can also occur if the environment changes gradually, for example- a result of formation of mountain ranges.

Ideas about Evolution Evolution-changes in inherited characteristics of a species over time. -A species is a group of organisms that share similar characteristics and can reproduce among themselves.

Charles Darwin- model of Evolution In December 1831 Charles Darwin, a young naturalist, sailed from England on a journey to South America on the HMS Beagle. He recorded observations on plants and animals. He was amazed by what he found on the Galapagos Islands.

He observed the beaks of finches are related to its eating habits. He also noticed the finches were similar to a finch species he had seen on the South American Coast. He found they had to compete for food, and those with beak shapes that allowed them to eat available food survived.

Darwin’s model of Evolution He hypothesized that plants and animals on islands off the coast of South America originally came from central and South America. He observed that the species of finches on the islands looked similar to a mainland finch species. He reasoned that members of a population best able to survive and reproduce will pass their traits to the next generation; over time. Differences can result in separate species. He published - THE ORIGIN OF SPECIES in 1859 Darwin’s hypothesis became known as the the theory of evolution by NATURAL SELECTION-organisms with traits best suited to their environment will more likely survive and reproduce

Adaptations An adaptation is a characteristic of a species that enables the species to survive in its environment. Scientists classify adaptations into three categories: STRUCTURAL- adaptations that involves shape, size, color and other features. BEHAVIORAL- involve the way organisms act. FUNCTIONAL- involve internal body systems that affect organisms biochemistry. An adaptation in which one species resembles another is mimicry. Camouflage involves a species blending in with their environment.

2. Homologous body parts- body parts that indicate two or more species share common ancestors

3. Vestigial structures- structures that don’t seem to have a function but might have once functioned in an ancestor.

Direct evidence- such as the development of antibiotic resistance in bacteria; support evolution. Indirect evidence supporting evolution: 1. Embryology- the study of embryos and their development, shows similarities amongst all vertebrate species

VARIATION- an inherited trait that makes an individual different from other members of its species Adaptation- a variation that makes an organism better suited to its environment. Many environmental factors can cause change in the source of genes.

Geographic Isolation- can make two populations so different they become different species.

Two models explain the speed of evolution Gradualism- describes evolution as a slow, ongoing process The Punctuated Equilibrium model says gene mutation can result in a new species in a relatively short time.

CLUES ABOUT EVOLUTION Fossils found in Sedimentary rock show evidence that living things evolved. Fossil age can be determined by two basic methods. 1.Relative dating- looks at the fossil location in a particular layer or rock; older rock layers are under newer rock layers.

2. Radiometric Dating- compares the amount of radioactive element with the amount of nonradioactive element in a rock

Fossil records have gaps. Incomplete rock record; most organisms do not become fossils Enough fossils have been discovered for scientists to conclude that complex organisms appeared after simpler ones. Most organisms that have ever existed are now extinct

DNA can provide evidence about how closely related organisms are.

THE EVOLUTION OF PRIMATES PRIMATES- groups of mammals with: 1. Opposable thumbs 2. binocular vision 3. flexible shoulders

Hominids- appeared 4 to 6 million years ago and had larger brains then apes. Fossils such as Australopithecus, point to Africa as the origin of Hominids. Homo-habilis and Homo erectus are thought to be early human ancestors Lucy

Lucy- australopithicus

Homo- Sapiens- Began evolving 400,000 years ago Neanderthals – had short heavy bodies with thick bones, small chins, and heavy brow ridges. Disappered about 30,000 years ago Not thought to be direct ancestors of modern humans Cro –Magnon fossils date from around 10,000 to 40,000 years ago; are thought to be direct ancestors of early Homo Sapiens.