1. The History of Life EQ: When did life form on earth?
Presenter notes: Life is what makes our planet different. As far as we know Earth is the only planet in the Solar System ever to have harbored life, although it is not impossible that it may have once existed on Mars in the distant past. Life is hugely important for the way our planet works and has altered almost every aspect of it’s atmosphere, ocean and land. This talk discusses the History of Life from the earliest times to the present day. Being a historical account of how life evolved, it does not deal with the process by which that change happened. This is examined in depth in a companion talk on Evolution.
Background note: The companion talk on Evolution can be downloaded from the Your Earth website:
© NASA 1

2. Diversity (1): Simple organisms
Bacteria
en.wikipedia.org/wiki/Image:Halobacteria.jpg
Two types of organism exist on our planet. One group has simple cells with DNA strands floating in a capsule. These prokaryotes, as they are called, include various types of bacteria

3. Diversity (2): Complex organisms
en.wikipedia.org/wiki/Image:Chlamydomonas_(10000x).jpg
en.wikipedia.org/wiki/Image:Laurencia.jpg
Golden algae
Fungi
Protozoa
A second group, eukaryotes,
have complex cells that have
compartments with special jobs
and DNA in a nucleus
Plants
Animals
en.wikipedia.org/wiki/Image:Elephant_near_ndutu.jpg
en.wikipedia.org/wiki/Image:Amanita_muscaria_(fly_agaric).JPG

4. The Fossil Record Fossils provide a record of life forms that once
existed in the past

5. Geological Time The whole geological timescale
The Phanerozoic in detail
The study of fossils in the context of the 4500 million years of
geological time allows us to piece together the History of Life

6. In the Sea (1): Bombardment
Early Earth
Cratered moon
Mars ?
© Julian Baum with permission
NASA
NASA
During its early history, the Earth was bombarded by meteorites.
Such inhospitable conditions probably prevented life from evolving.
million years ago

7. In the Sea (2): First living things
Life evolved
shortly after the
bombardment
ended, early in
Earth History.
The first living
things were
simple bacteria
Modern bacterial mounds
Fossil bacteria?
en.wikipedia.org/wiki/Image:Stromatolites_in_Sharkbay.jpg
million years ago

8. In the Sea (3): Oxygen Early photosynthetic bacteria produced
oxygen and released
it as a waste product.
This added oxygen
to the atmosphere
for the first time.
Iron oxide rocks
Photosynthetic
bacteria
Presenter notes: This talk has three parts. In the first part, we will discuss the early history of life and see how life began in the Sea about 3800 million years ago. In the first activity we will then examine the ecology of one of the most famous fossil sites anywhere in the world: the Burgess Shale of British Columbia, Canada. In the second part, we will learn about the invasion of land, which began about 500 million year ago, and in the following activity we will compare two early land ecosystems and think about the progressive development of food webs. Finally, in the third part, we will see how life continued to diversify to the present day, but was occasionally subject to waves of extinction. Five mass extinctions have occurred over the past 500 millions and have profoundly shaped Life on Earth. We will conclude by asking whether human activity is now triggering a sixth mass extinction.
en.wikipedia.org/wiki/Image:Anabaena_sperica.jpg
million years ago 8

9. In the Sea (4): Complex cells
Acritarch
Two billion years later complex
eukaryote cells appeared.
These had compartments with
special functions such as energy
factories called mitochondria.
Eukaryote cells need oxygen -
this explains their late evolution
Presenter notes: The second group of organisms, which we call eukaryotes, have complex cells that have compartments with special jobs and DNA located in a nucleus. This group includes the familiar kingdoms of organisms like animals, plants and fungi. Most of the organisms in these kingdoms are multicellular, made up of many cells working together. However, other eukaryotes include the single-celled kingdoms of the protozoa and the ‘golden brown algae’ or chromists.
1900 million years ago 9

10. In the Sea (5): Multicellular life
Grypania
After another half billion years
many-celled life appeared
Grypania was a coiled
tube, 2 mm wide and up to
5 cm long
© Bruce Runnegar with permission
1400 million years ago

11. In the Sea (6): Biology’s Big Bang!
evolution.berkeley.edu/evolibrary/images/bangiomorpha1.jpg
Red algae
en.wikipedia.org/wiki/Image:Sexual_cycle.svg
A short time later, 1200 mya, algae evolved sexual reproduction
1200 million years ago

12. In the Sea (7): Ediacara Evidence
By 630 mya, the familiar kingdoms of animals, plant and fungi
had evolved. The Ediacara fauna of this time interval were strange
bizarre organisms from the dawn of animal life
million years ago

13. Beginnings (8): Diversity explodes
palaeo.gly.bris.ac.uk/palaeofiles/lagerstatten/Burgess/Anomalocarishunts.jpg
Fossils/Anomalocaris-canadensis.jpg
Burgess Shale fossils
Claw of Anomalocaris
Presenter notes: When organisms die they may leave behind a record in the form of their skeleton or shell or stem. These fossil remains can survive for millions and sometimes billions of years. Palaeontologists extract fossil remains from the rock and use them to piece together the History of Life. Organisms are only preserved in special conditions so only a tiny proportion of all living things ever become fossils. Consequently the fossil record is incomplete and many questions remain unanswered about the History of Life. Nevertheless in general terms the fossil record gives a surprising clear insight into the historical sequence of events that gave rise to the life we see around us today.
Around 542 mya, several fossil sites show that the diversity of
animal life on Earth dramatically exploded over a short time.
million years ago 13

14. Left Side Activity Draw the entire geological timescale.
Presenter notes: When organisms die they may leave behind a record in the form of their skeleton or shell or stem. These fossil remains can survive for millions and sometimes billions of years. Palaeontologists extract fossil remains from the rock and use them to piece together the History of Life. Organisms are only preserved in special conditions so only a tiny proportion of all living things ever become fossils. Consequently the fossil record is incomplete and many questions remain unanswered about the History of Life. Nevertheless in general terms the fossil record gives a surprising clear insight into the historical sequence of events that gave rise to the life we see around us today.
million years ago 14