Download Lesson 8 – History of Life

Build Your Own Planet
Lesson 8: The History of Life on Earth
Group: ___________________________
Look at the timeline that the class has just assembled. Discuss the following
questions with your group and record some ideas in the spaces below.
Has life been complex or simple during most of Earth’s history? ______________
(Complex means made up of many cells. Simple means made up of just one cell.)
Has life been microscopic or macroscopic during most of Earth’s history?
___________________________
Has most life been in the oceans or on the land during most of Earth’s history?
___________________________
What are some things you notice about the way that life has evolved on Earth?
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
Refer to lesson #5. How old is the star that your planet is orbiting?
_____________
Assume that your planet is as old as your star. Above the timeline of Earth’s
history is another timeline. This one starts at 0 and goes up to 5 billion years.
Find your planet’s age on this timeline. If your planet is more than 5 billion years
old, estimate how far beyond the end of the timeline your planet would be.
If your planet is less than 4.6 billion years old:
Look down from the upper timeline to Earth’s timeline. Was there any life
on Earth at that time? Yes / No (circle)
If the answer is yes, think about what the life on Earth was like then.
Where did it live? Ocean only / Land and ocean (circle)
Was it:: simple, single-celled / complex, multi-celled (circle)
How big was it? Microscopic / Macroscopic (circle)
Had it developed any hard body parts yet? Yes / No (circle)
Had it developed a backbone yet? Yes / No (circle)
Had it developed intelligence yet? Yes / No (circle)
If your planet is greater than 4.6 billion years old:
What is one way life on Earth has changed over the last 1 billion years?
_________________________________________________________________
What is one way life on Earth has changed over the last 500 million years?
_________________________________________________________________
What is one way life on Earth has changed over the last 5 million years?
_________________________________________________________________
How much longer has life evolved on your planet than on Earth? ___________
How might life on Earth change that same length of time into the future?
_________________________________________________________________
_________________________________________________________________
All Groups:
Pretend that life on your planet evolves at the same rate as life on Earth. What
do you think it will be like when you explore the planet?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
Where might you find it?
_________________________________________________________________
What should you look for?
_________________________________________________________________
Do you think it is likely that life on your planet will evolve at the same rate as life
on Earth? Why or Why not?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
Two important points:
1) We have no way of knowing how rapidly life might evolve on other planets.
Although it is possible that on some planets life might change at a rate similar to
Earth’s, there is no reason to assume that it must. On some planets it seems
highly unlikely life would evolve at the same rate as Earth’s.
2) Although life on a planet may evolve into complex, multi-celled forms, that
does not mean that all life will be that way. On Earth, even though we have
complex life forms like humans, trees, and fish, we still have a lot of simple,
microscopic life around similar to some of the earliest things living on our planet.
Today there are a lot more bacteria on Earth than mammals.
These two points should be kept in mind as you search your planet for signs of
life.