Download The Origins of the Solar System

The Origins of the Solar System
Read the section below and answer the questions at the bottom.
How do we know how the solar system formed and how long ago? The oldest rocks on Earth
have radiometric dates to about 4 billion years, and rocks on the Moon and asteroid and meteorite
material we have collected on Earth date to 4.6 billion years. Based on these dates we believe the
Earth is about 4.6 billion years old. The premise is that the Moon formed at the same time as the
Earth and asteroids and meteorites formed at nearly the same time. The planetary accretion (to
build up by pieces) model is how we understand the solar system formed. Based on what we
have observed occurring around other stars, computer modeling and observation, the solar system
was formed from a vast cloud of gas and dust that was the remains of the destruction of one or
more giant stars about 5 billion years ago. Under the law of gravitational attraction this cloud
began to rotate and clump together forming the Sun at its center and the planets outward from the
Sun. As the dust and gas rotated and formed our solar system it flattened so the planets all lie on
one plane, the equatorial plane. The planets are also all revolving in the same direction around
the Sun, another clue to the accretionary hypothesis. The early planets grew in size as they were
constantly bombarded by smaller planetesimals (smaller proto-planets) and the craters on the
Moon, Mercury and Mars and many of the other moons in the solar system are evidence of these
early collisions. Towards the end of this bombardment period some of the planets were struck so
hard as to tilt their axes (Earth), change the direction of their rotation (Venus) and even tip them
90° to the equatorial plane (Uranus). Our Moon is believed to have been the result of a collision
with a Mars size planetesimal that melted the Earth completely and blew off the upper layer of
Earth forming the Moon. When most of the early left-over planetesimals were absorbed by the
planets the bombardment period ended, but occasional collisions still occur with what remains.
The asteroids and comets are the remains of the material that did not become integrated into the
planets and continue to orbit the Sun occasionally colliding with planets and the Sun. Jupiter
being the largest planet tends to get hit by comets relatively frequently and was hit in 1994 and
possibly July 2009. We have good evidence that the Earth was hit by an asteroid 65 million years
ago leading to the eventual extinction of the dinosaurs as well as a majority of life in Earths
oceans. Comets frequently hit the Sun and all the planets are vulnerable to future strikes
Answer the questions below using the backside of the page if you need more room.
1. How old are the oldest rocks on Earth? How old is the Moon, asteroids and meteorites?
When did the solar system begin to form?
2. What is the name of the model for the early formation of the solar system? What does
accretion mean? What force caused the gas and dust cloud to rotate, flatten and accrete?
3. What is the name of the plane that the planets lie on? What does the evidence that the planets
all revolve in the same direction say as regards the planetary accretion model? What are
planetesimals? How did they contribute to the size of the planets? What do we call the period
when planetesimals were colliding into the planets? What are craters evidence of?
4. Why is Venus rotating opposite the direction of the other planets? Why is Uranus tipped 90°
to the equatorial plane? How did our Moon form?
5. What material remains from the end of the bombardment period? What planet is frequently hit
by comets? Why? What hit the Earth 65 million years ago? What impact did it have for life on
Earth? Can collision still occur in the future? Why?