UNIT 4: History Of Biological Diversity

CHAPTER 14: The History of Life

PAST NOW FUTURE?

What is this?

Earth’s Early history

• Approximately 4.6 billion years ago, the Earth was formed when many pieces of cosmic debris became attracted to each other.

• As Earth was struck by large objects it heated and melted the elements that Earth was made of causing the elements to arrange themselves from most dense (at Earth’s core) to the least dense that are on the surface of the Earth.

• The lightest elements escaped to Earth’s surface and became the atmosphere.

• At first the atmosphere was made of water vapor, carbon dioxide, sulfur dioxide, carbon monoxide, hydrogen cyanide, hydrogen sulfide, nitrogen and hydrogen. There was little or no free oxygen.

Clues in Rocks• About 500 million years after Earth was

formed it cooled enough for liquid water to form our oceans. This is when the first life appeared.

• The fossil record holds clues to the first life forms that existed 3.5 billion years ago.

• Fossils: are the preserved evidence of an organism.

•

6 Categories of Fossils

• About 99 % of the species that have ever lived are now extinct and only a tiny percentage of those organisms are fossilized.

• Fossils are only created in certain conditions.

• Fossils are most commonly found in sedimentary rocks.

• Sedimentary rocks: are formed when silt, sand, or clay builds up in the bottom of a river, lake or ocean.

• As they layer over each other the pressure becomes greater on the bottom layer and it turns this layer into rock such as sandstone and limestone.

• Each of these layers can be identified with a time period in history. This is called Relative Dating.

Fossil Formation

Relative Dating

• Relative dating is a method used to determine the age of rocks by comparing them with those in other layers.

• Fossils cannot be formed in igneous or metamorphic rocks.

• Fossils do not usually survive the great amounts of heat and pressure needed to form these rocks.

• Paleontologists are scientist that study fossils. They piece together the past based on fossils records and infer how and organism lived in their environment

Radiometric Dating• Uses the decay of radioactive

isotopes to measure the age of a rock

• About 100 years ago scientists discovered that certain elements are radioactive- meaning they are unstable and over time they break down to become more stable.

• The break down of a radioactive element is consistent for that element and is call it’s half - life

• Radioactive isotopes that can be used for radiometric dating are found only in igneous or metamorphic rocks

Dating Mummies…..

• Carbon-14 can be used to date substances like bones and tissues.

• But must be less than 60,000 years old because carbon has a relatively short half- life.

Geological Time Scale

• The geological time scale is a model that expresses the major geological and biological events in Earth’s history

• The geologic time scale is divided into the Precambrian time and the Phanerozoic eon

• Eras of the Phanerozoic eon include the Paleozoic, Mesozoic, and Cenozoic eras.

• Each era is divided into one or more periods

Precambrian

• Nearly 90 percent of Earth’s entire history, stretching from the formation of Earth to the beginning of the Paleozoic era about 542 million years ago

• Autotrophic prokaryotes enriched the atmosphere with oxygen.

The Paleozoic Era• The ancestors of most major animal

groups diversified in what scientists call the Cambrian explosion.

• Life in the oceans continued to evolve at the end of the Cambrian period.

• Fish, land plants, and insects appeared during the Ordovician and Silurian periods.

• The first tetrapods emerged in the Devonian

Wandering Continents

• 150 years ago, Geologists noticed that the continents looked like a jigsaw puzzle.

• They saw that the east coast of South Americacould comfortably fit against the west coast of Southern Africa.

• And that North America and Greenland could fit easily against Europe and Northern Africa

• In 1910, Alfred Wegener formed the hypothesis that Earth’s continents had moved.

• His hypothesis was that the continents had once been joined together in a single landmass and have since drifted apart.

• Wegener called this supercontinent Pangea

• Then around 225 million years, Pangea began to break apart and the land masses moved to their present day positions. This idea of continents drifting is called continental drift.

• Plate tectonics describes the movement of several large plates that make up the surface of Earth

• These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

The Cenozoic Era

• Mammals became the dominant land animals.

• After the mass extinction at the end of the Mesozoic era, mammals of all kinds began to diversify .

CH. 14.2 - Origins: Early Ideas

• Spontaneous generation is the idea that life arises from nonlife

• Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from rotting meat.

• The theory of biogenesis states that only living organisms can produce other living organisms.

• Louis Pasteur designed an experiment to show that biogenesis was true even for microorganisms

Origins: Modern Ideas

• Simple organic molecule formation

• The primordial soup hypothesis was an early hypothesis about the origin of life.

• Organic molecules could have been synthesized from simple reactions.

• UV light from the Sun and electric discharge in lightning might have been the primary energy sources.

Making Proteins

• Life requires proteins.

• One possible mechanism for the formation of proteins would be if amino acids were bound to a clay particle.

Genetic Code

• Some RNA sequences appear to have changed very little through time.

• Many biologists consider RNA to have been life’s first coding system

• Other researchers have proposed that clay crystals could have provided an initial template for RNA replication.

Cellular Evolution

• Scientists hypothesize that the first cells were prokaryotes.

• Many scientists think that modern prokaryotes called archaea are the closest relatives of Earth’s first cells

Photosynthesizing Prokaryotes• Archaea are autotrophic.They do not obtain

their energy from the Sun.

• Archaea also do not need or produce oxygen. They produce energy from inorganic substances.

• Many scientists think that photosynthesizing prokaryotes evolved not long after the archaea.

• Prokaryotes, called cyanobacteria, have been found in rocks as old as 3.5 billion years. They produced enough O2 to produce the ozone layer.

The Endosymbiont Theory

• The ancestors of eukaryotic cells lived in association with prokaryotic cells.

• The relationship between the cells became mutually beneficial, and the prokaryotes became organelles in eukaryotic cells.

• This theory explains the origin of chloroplasts and mitochondria.

The Endosymbiont Theory