The History of Life

Take a guess!• How old is the Earth?• When did the first living things appear on the planet?• When did the first humans appear on Earth?

Cosmos: The History of Life by Carl Sagan

An artist’s impression of how the very early universe might have looked during an intense period of hydrogen conversion into stars.

Further Reading: The Star in You

Matter is much older than life.

New types of atoms were synthesized inside hot stars.

The stars blew up, releasing the atoms into space.

Planets and everything else in the universe are composed of these atoms.

We are all made of star stuff!?

What is matter?• Matter includes atoms and particles that have a mass• Matter is also defined as anything that has mass and

occupies volume

What are atoms?• Basic unit of matter• Everything is composed of

atoms!• An atom consists of a heavy

nucleus surrounded by very light electrons

GEOLOGICAL TIME

• TOO OLD FOR YEARS OR MONTHS

• FOUR ERAS DEPENDING ON WHICH ORGANISMS LIVED

1. PRECAMBRIAN

2. PALEOZOIC

3. MESOZOIC

4. CENOZOIC

What is an Era?

• A very long time period (hundreds of millions of years)• Geologists divide the history of the Earth into eras

WHY DO WE HAVE DIFFERENT ERAS?

PRECAMBRIAN

• What do scientists think was alive way back then?• Bacteria• This early bacteria produced energy by

photosynthesis• This era lasted for billions of years until an oxygen

rich atmosphere developed and more living things evolved

Dr Gordon Beakes © University of Newcastle upon Tynelicensed

PALEOZOIC ERA540 MILLION YEARS AGO!!

• NOW THE EARTH IS GETTING LARGER LIFE! • FIRST PART OF PALEOZOIC IS CALLED CAMBRIAN• PROTISTS!• SEA PLANTS!• SEA ANIMALS!• LAND PLANTS!• LAND ANIMALS!• WHAT ENDED THE PALEOZOIC ERA?? • MASS EXTINCTION!

MESOZOIC ERA245 MILLION YEARS AGO!!

• DINOSAURS• REPTILES• SMALL MAMMALS APPEAR• BIRDS EVOLVE• PLATE TECTONICS• WHAT ENDED THE MESOZOIC ERA?• MASS EXTINCTION!• ? METERORITE

• Mesozoic Means “Middle Animals”• Huge changes in how both plants and animals looked

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

http://geology.utah.gov/utahgeo/dinofossil/dinoage.htm

Image courtesy of the UC Museum of Paleontology Understanding Evolution: http://evolution.berkeley.edu."

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

CENOZOIC ERA66 MILLION YEARS AGO!

• MAMMALS FLOURISH• PRIMATES ABOUT 30 MILLION YEARS AGO• MODERN HUMAN SPECIES – ABOUT 200,000

YEARS AGO

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Tom Tregenza © Tom Tregenza

Tom Tregenza © Tom TregenzaTom Tregenza © Tom Tregenza

Dr Gordon Beakes © University of Newcastle upon TyneProf Paul F. Brain © University of Wales, Swansea

licensed for use through the Centre for Bioscience ImageBank,http://www.bioscience.heacademy.ac.uk/imagebank/"

• Bacteria and other single-celled organisms were among the first living things to appear on Earth

• First appeared 4,500 million years ago, during the Precambrian period

4,500,000,000 years ago!

HOW WERE THE FIRST CELLS MADE?

Louis Pasteur

Miller and Urey

Francesco Redi

Scientists used to believe that dead chemicals would suddenly come to life.

Spontaneous Generation Video Clip

Animation: Louis Pasteur’s Experiment

In 1668, Italian physician Francisco Redi proved that dead meat does not give rise

spontaneously to maggots.

In 1864, Louis Pasteur proved two things with his “boiled broth” experiment:

1. Microorganisms are present in the air and can contaminate solutions

2. The air itself does not create microbes

Miller and Urey: Abiogenesis

Abiogenesis is the study of how life arises from non-living matter through natural

processes

Video about The Experiment

Miller and Urey: Abiogenesis

In 1953, Stanley Miller and Harold Urey showed that organic compounds, which

are essential to cellular life, could be produced under early-Earth conditions

The Answers• How old is the Earth?• About 4.6 billion years old!

• When did the first living things appear on the planet?• About 3 billion years ago

• When did the first humans appear on Earth?• Earliest human ancestors (hominids) appeared 5

to 8 million years ago• Modern humans (homo sapiens) first appeared

about 200,000 years ago

• Bacteria and single-celled organisms were the first forms of life to appear on earth

• How did these simple bacteria “change into” the diversity of life found on the planet today?

To Ponder…