The past, present, and future of our planet and the life on it
A history of life on earth Learning goals The earth has a very long geologic history We can find out about it by looking at rock layers & fossils Modern animals arrived late, and humans arrived VERY recently
A history of life on earth How old is the earth? How old is the oldest evidence of life? How long was it before complex, multicellular life appeared?
A history of life on earth How old is the earth? How old is the oldest evidence of life? How long was it before complex, multicellular life appeared? How would you find out if you don’t know?
A history of life on earth Finding out stuff Using an enzyclopedia: is free Using google: – but you may have to try putting in your question several ways Using books: Science textbooks in a library; may take a while to find what you are looking for
A history of life on earth If one year was 1 inch, then 1 billion years is about miles – that is the driving distance from Flagstaff to Anchorage, Alaska, back to Flagstaff, and then down to the tip of South America, and back to Flagstaff again. 4.6 billion years is around the earth almost 3 times!!!
A history of life on earth How old is the earth? 4.5 billion years How old is the oldest evidence of life? 3.8 billion years When did complex, multicellular life appear? 0.7 billion years ago How did scientists find this out? Mostly by dating rocks using radioisotopes (chemical elements that decay over time at known rates)
A history of life on earth
The Hadean era: 4 billion years ago no life anywhere no oxygen in the atmosphere
A history of life on earth The Archean era: billion yrs ago no life on land bacterial life in the sea & on shores oxygen slowly released by bacteria
Protists, fungi, bacteria Early life on earth Stomatolites: complex communities of (mostly) cyanobacteria - produced all the atmospheric oxygen
A history of life on earth Stomatolites complex communities of (mostly) cyanobacteria - produced all the atmospheric oxygen
A history of life on earth The Archean era: billion yrs ago no life on land bacterial life in the sea & on shores oxygen slowly released by bacteria
A history of life on earth The Proterozoic era: billion yrs ago still no life on land first more complex cells & animals / algae in sea - but these looked nothing like what we know today!
A history of life on earth ‘Ediacara fauna’ – first multicellular life? (Named after Ediacara hills in Australia where fossils were found)
A history of life on earth The Palaeozoic, Mesozoic, Cenozoic: 0.5 billion yrs ago until today animals we would recognize today appear around 0.5 billion years ago first animals & plants on land billion years ago (that’s 450 million million)
A history of life on earth ‘Burgess shale fauna’ – first animals with skeletons? (Named after a type of rock found in Canadian Rockies)
Geology: study of rocks Side story: geology Igneous rock Metamorphic rock Sedimentary rock
Side story: geology
A history of life on earth
How do scientists find out what animals lived millions of years ago? Dating of rocks again (radioisotopes) Dating of carbon material from plant remains (carbon isotopes) Rock layering gives the order of events Tree ring research
Each layer is a different time period Younger periods on top Each layer may contain fossils Size & kind of grains is informative
Continental Drift continents move on plates explains earthquakes, volcanoes, mountain ranges, troughs in the sea, structure of sea floor, and fossil locations Side story: how did sea & land areas change? Sea levels also change if global climate changes
A history of life on earth Evolution of life on land Were animals or plants first? Animals were first! Land-plants (not algae) only appeared about 450 million years ago. When did the first flowering plants appear? Only about 120 million years ago! Before that, ferns, mosses, and algae (incl. kelps etc.) When did mammals appear first? Before dinosaurs! ~220 million years ago.
A history of life on earth Origins of animal & plant groups
A history of life on earth
Side story: how did life get complex? The ‘Major Transitions’ E. Szathmary and J Maynard Smith:
The ‘Major Transitions’ Complexity always increases when smaller units come together to form a bigger unit Often this requires complex communication and conflict control E. Szathmary and J Maynard Smith: Side story: how did life get complex?