Geologic Time
Our Planet’s History Geologic time is the time frame of our planet’s history. While 30,000 year old cave paintings seem really old to us when compared to modern art, this is a miniscule amount of time in comparison to the age of our planet. Earth has been in existence for 4,600,000,000 years. 4.6 billion years!
How do Scientists Know the Earth’s Age? When scientists discovered radioactivity, they were able to develop radiometric dating methods to determine the age of ancient rocks. The consistency of the results gives scientists confidence that the ages are correct to within a few percent. Ancient rocks exceeding 3.5 billion years in age have been found on all of Earth's continents.
When did humans first appear? 4,600,000,000 years includes… The birth of our planet Evolution of the first single-celled life-forms Assembly of at least three supercontinents (Rodinia, Pannotia, and Pangaea) The rise and fall of dinosaurs The colonization and dominance of flowering plants When did humans first appear?
Modern Cro-Magnon humans showed up less than 50,000 years ago. Understanding the true meaning and scale of Geologic Time can be challenging, so today we are going to do two activities to help you put Geologic Time in perspective.
Activity #1: Clapping the Earth’s Life Let’s represent one decade (10 years) in seconds. Each year will be represented by one second which equals one clap of the hands. 1 clap = 1 second = 1 year How long does it take to clap your age? If your grandmother is 70, how long will it take to clap her age?
How long would it take to clap the age of this 100-year-old tortoise in… seconds? __________ minutes? __________________ (Remember: there are 60 seconds per minute) 100 sec and 1 min 40 sec
How long would it take in minutes… To clap the age of the 234-year-old Declaration of Independence? 234 seconds 60 sec/min = __________min To clap the age of the Great Pyramid of Egypt built 4571 years ago? 4571 seconds 60 sec/min = _________ min 3.9 min and 76.18 min
How long would it take to clap the Earth’s Age, 4.6 billion years? Do you think you could clap the Earth’s Age in your own lifetime? Circle one. YES NO
The Calculation… There are 60 seconds per minute 60 sec/min X 60 min/hr = 3,600 sec/hr 3,600 sec/hr X 24 hrs/day = 86,400 sec/day 86,400 sec/day X 365.25 days/year = 31,557,600 sec/year How long will it take to clap 4,600,000,000 seconds? 4,600,000,000 seconds 31,600,000
4,600,000,000 seconds 31,600,000 seconds/year = That’s almost 145 years! Remember, your own lifetime can be clapped in less than 15 seconds!
Activity #2: TP Timeline Now we are going to make a TP Timeline! The tissue we’re using contains 176 sheets per roll. The entire roll represents the earth’s lifetime, so we need to figure out how many years each square sheet of tissue will represent. 4,600,000,000 176 sheets = 26 million years/sheet
Major Earth Events We are going to label the tissue timeline to mark significant events in the Earth’s history. We’ll start from today and work backward in time.
TP Timeline Early modern humans – 130,000 years ago. That’s 0.5% of one sheet from today (the edge of the first sheet) The first hominids – 7,000,000 years ago 27% of one sheet from today Many dinosaurs go extinct – 65,000,000 years ago. 2.5 sheets from today First bird fossils formed – 174,000,000 years ago. 6.7 sheets from today “The Great Dying” – 245,000,000 years ago 9.4 sheets from today First fish, first insects – 490,000,000 years ago 18.8 sheets from today
Abundant shell life = 542,000,000 years ago 21 sheets from today Oxygen occurs in Earth’s atmosphere – 2,000,000,000 years ago. 76 sheets from today First life forms (prokaryotes) – 3,600,000,000 years ago 138 sheets from today Oldest rocks on Earth – 4,000,000,000 years ago. 154 sheets from today (22 sheets from the Earth’s origin) Formation of Earth – 4,600,000,000 years ago end of the roll of paper!
Reflection Complete an exit slip answering the following prompts: Today I learned for the first time that… This makes me think about… Now I am curious to know…