History of the Earth

Ch. 32

What Important Historical Events can you name and date?

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• Dinosaurs

• Oldest Living Organism

• Oldest Rock

• Age of the Earth

Team finds Earth's 'oldest rocks' By J ames Morgan Science reporter, BBC News

Earth's most ancient rocks, with an age of 4.28 billion

years, have been found on the shore of Hudson Bay,

Canada.

Writing in Science journal, a team reports finding that a

sample of Nuvvuagittuq greenstone is 250 million years

older than any rocks known.

I t may even hold evidence of activity by ancient life forms.

I f so, it would be the earliest evidence of life on Earth - but

co-author Don Francis cautioned that this had not been

established.

"The rocks contain a very special chemical signature - one

that can only be found in rocks which are very, very old,"

he said.

The professor of geology, who is based at McGill University

in Montreal, added: "Nobody has found that signal any place else on the Earth."

"Originally, we thought the rocks were maybe 3.8 billion years old.

"Now we have pushed the Earth's crust back by hundreds

of millions of years. That's why everyone is so excited."

Ancient rocks act as a time capsule - offering chemical

clues to help geologists solve longstanding riddles of how

the Earth formed and how life arose on it.

But the majority of our planet's early crust has already

been mashed and recycled into Earth's interior several

times over by plate tectonics.

Before this study, the oldest whole rocks were from a 4.03

billion-year-old body known as the Acasta Gneiss, in Canada's Northwest Territories.

The only things known to be older are mineral grains called zircons from Western Australia,

which date back 4.36 billion years.

Date range

Professor Francis was looking for clues to the nature of the Earth's mantle 3.8 billion years

ago.

He and colleague J onathan O'Neil, from McGill University, travelled to remote tundra on the

eastern shore of Hudson Bay, in northern Quebec, to examine an outcrop of the Nuvvuagittuq

greenstone belt.

The rocks contain structures which might indicate life was present

Timelines…

Experiencing Geologic Time:

• How long would it take to count to a million?(1,000,000)

1,000,000 “yrs” 1 sec 1 min 1 hr 1 day = 5.8 ≈ 6 days!

“yrs” 60 sec 60 min 24 hr

A thousand millions is a “billion”

• How many years would it take to count to a billion? (1,000,000,000)

(Show the calculation for extra credit)

Geologic Time at Scale:visualizing

544 my5000 my

~ 12% of Earth History

The “ages” of Geologic TimeStep # of years ago Events Period EpochPrecambrian era45 ~4.5 billion Formation of Earth38 ~3.8 billion Oldest Rocks36 ~3.6 billion First Fossils - algae/bacteria20 ~2.0 billion Oxygen Pollution of atmosphere16 ~1.6 billion First animal fossils - worms/stromatolitesPaleozoic era6 ~530 million Trilobites, seaweeds, first vertebrates (fish) Cambrian Explosion5 ~490 million Early fishes, first insects, Marine invertebrates thrive Ordovician4.5 ~440 million First land plants and animals, bony fish and marine invertebrates Silurian4 ~410 million Sharks common Devonian3.5 ~355 million First amphibians, ferns common Mississippian3 ~325 million First reptiles and conifers Pennsylvanian2.5 ~290 million Pangaea forms, mass extinction, deserts form PermianMesozoic era2 ~230 million First dinosaur and mammal fossils Triassic1.5 ~175 million First bird fossils Jurassic0.6 ~65 million Dinosaurs become extinct CretaceousCenozoic era0.5 ~50 million Adaptive radiation of mammals Tertiary (Paleocene)0.4 ~40 million Antarctica and Australia separate (Eocene)0.3 ~30 million First elephants with trunks (Oligocene)0.25 ~25 million First grassland ecosystems (Miocene)0.05 ~5 million Panama land bridge forms (Pliocene)

0.01 ~1 million Ice ages, mammoths and mastodons Quaternary (Pleistocene)0.005 ~500 thousand Neanderthal fossils0.0001 ~10 thousand Neolithic period of human history (Holocene)

Look at page 600 in your Textbook

Hadean, Archaen and Proterozoic Eons(the first 4.1 billion years)

Phanerozoic Eon(the last 500 million years)

Investigating Geologic Time

Relative Time1. Index fossils2. Stratigraphy

• Law of superposition• Unconformities

Absolute Time1. Tree Rings2. Sediment Layers (varves)3. Radioactive decay

Stratigraphy Exercises

Radioactive Decay Problems

Microfossils, Sediments and Sea Floor Spreading

Chapter 32 Section I, II and III

Video Preview of Ch. 32

Video Assignment

• Geologic Time

• Life in Earth’s Past• Events in Earth’s Past