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Evolution of the Solar System
Rasc-AL Forum 2005
About Explore!

Activity - Timeline Lineup


Students ages 12–17 work in groups or as a class to determine the order of events that formed our solar system. This is an excellent activity to begin discussion of events that shaped the solar system and how Earth's geosphere and biosphere have changed — in an interrelated manner — through time. It also is a strong assessment activity.

What's Needed?

For a class activity:

  • Master list of selected events and time of events for the facilitator
  • One event index card per student, each with a single, different event listed
  • 50 meters (164 feet) of string with tape “flags” every 1 meter (each meter = 100 million years)

Alternatively, devise a scale based on available space

For a group activity:

  • Master list of selected events and time of events for the facilitator
  • One set of event index cards per student group (10 to 30 total events)
  • 1.5 meters (5 feet) of string with tape “flags” every 30 centimeters (1 foot) = 1 billion years) or use masking tape with divisions marked, instead of string

Before You Start

Select solar system formation/Earth development events pertinent to your curriculum needs, age of students, and interests of students. A list of possible events to choose from appears below.

Consider using events that defined the geology of your state (The Road Side Guide to Geology for your state is one reference that presents such information in an easily digestible fashion).

Record each event on a separate index card (without ages). Prepare one card per student, or a set of cards per student group.


There are many ways to present this activity. Here are two suggestions:

  1. Provide each student with an event card and invite them to work together as a class to determine which events happened first, second, third, and so on. Have the students arrange themselves as a human timeline across the room.
  2. Provide each small group of students with a complete set of event cards and have the group work together to arrange the events in order (floor or table space is needed to lay out the cards).

As the students are arranging themselves or their cards, circulate and discuss the logic behind ordering the events (e.g., dinosaurs had to be present on Earth before they could become extinct).

When the students have placed themselves or their cards in order, challenge them to think in terms of the actual timing of events and have them place their cards along the timeline.

As a class, discuss the events and their timing. Connect related events where possible. (For example, Earth's earliest organisms lived in an anoxic world. Oxygen was added later when photosynthetic organisms evolved. Once oxygen built up the atmosphere, an ozone layer developed. This layer blocks harmful ultraviolet light and may have provided protection to multicellular organisms and aided in their evolution, etc.). Have the student rearrange themselves or their cards as you visit each event.

At the close of the activity, ask the students for their broad observations about the order and timing of events.

Some Big-Picture Ideas:

  • The components of our solar system all formed at the same time — and formed quickly!
  • Earth and the other terrestrial planets were dominated by physical activity for much of their early history (formation, bombardment by asteroids, volcanism, formation of layers — core, mantle, crust; in the case of Earth and possibly Mars, formation of oceans).
  • The terrestrial planets are cooling. Small bodies, like the Moon and Mercury, are geologically inactive because they have cooled; they no longer have interiors hot enough to produce volcanic activity at the surface.
  • Even though the period of intense bombardment ended almost 4 billion years ago, occasional impacts occur on all planets. Such impacts can influence Earth's biosphere.
  • The biosphere got underway ~1 billion years after Earth formed, but was dominated by single-celled prokaryotes for a loooooooooong time.
  • Multicelled animals and plants did not make it onto the scene until ~600 Ma (million years ago).
  • The seas teamed with life, but land was dominated by bacteria and slime and such until only ~430 Ma.
  • Historical records of human activity are very recent with respect to duration/geologic time.
  • Hominids (bipedal, upright walkers) are recent, and Homo sapiens are REALLY recent.

Invite the students to explore the Evolution of Our Solar System Timeline to learn more about how Earth and our solar system have changed through time.


  • Have the students create event cards based on their research. Substitute these cards for those used in the activity.
  • Invite the students to use the events to create a board game.
  • Have the students research events and create an illustrated timeline mural that can be hung on the classroom walls.

Selected Solar System and Earth Events*

Choose from the events below or use events that are pertinent to your curriculum needs.

Bold text can be used on the index cards, or it can be phrased so that the language is appropriate for the age level of the children. Non-bold text is intended for use by the facilitator.

4.56 Billion Years Ago

Solar Nebula Forms
A concentration of hydrogen gas and dust swirling around our young Sun.

Solar Nebula Forms
4.56 Billion Years Ago   Planetesimals Form
Baby planets less than a few kilometers across form.
4.56 Billion Years Ago   Planetesimals Grow Up to Form Protoplanets
Planetesimals are large enough to attract material through gravity.
4.56 Billion Years Ago   Terrestrial Planets Form
Mercury, Venus, Earth, and Mars form in the hot inner solar system.
4.56 Billion Years Ago   Gas Giants Form
Jupiter, Saturn, Uranus, and Neptune form in the cooler, outer solar system.
  Gas Giants Form
4.56 Billion Years Ago   Pluto Forms
Pluto, our ninth planet, is considered by some to be more related to the objects in the Kuiper belt, a band of rocky icy bodies that lie beyond Neptune's orbit.
4.56 Billion Years Ago   Solar System Cleaned Up
“Leftovers” in the solar nebula are blown into the outer solar system when nuclear fusion gets going in our Sun.
4.56 Billion Years Ago   Formation of Rocks in Space . . . AsteroidsAsteroid    
4.56 Billion Years Ago   Formation of Dirty Snowballs in Space . . . Comets    
4.5 Billion Years Ago   Formation of Earth's Moon
Earth was hit by a Mars-sized planet. Debris blown into space around Earth eventually coalesced and formed our Moon.
4.5 Billion Years Ago   Magma Ocean on the Moon!
The coming together of the particles forming our Moon created heat — enough heat to melt the outer layer of the Moon!
  Magma Ocean on the Moon!
4.4 Billion Years Ago   Initial Crust on Earth
Early Earth was HOT. Eventually the molten outer layers cooled, forming a crust. This crust was probably a bit like our ocean crust today.
4.5 Billion Years Ago   Oldest Moon Rocks
The Moon's magma ocean cooled, allowing a crust to form. Apollo Astronauts collected Moon rocks from some of this ancient crust.
4.2 Billion Years Ago   Formation of Earth's Early Atmosphere and Oceans
Volcanos spewed gases — including water vapor — into the atmosphere. When things cooled down enough the water vapor condensed as liquid water in our oceans.
  Formation of Earth's Early Atmosphere and Oceans
3.7 Billion Years Ago   Mercury Chills Out
This small planet became geologically inactive
3.5 to 4.5 Billion Years Ago   Oceans on Mars?
Early Mars may have had an ocean in its northern hemisphere. Features interpreted to be ancient river valleys are carved into the surface of Mars, suggesting the presence of water.
4.0 Billion Years Ago  

Oldest Rocks on EarthOldest Rocks on Earth
Continental crust (land!) had formed by this time. Samples from Australia have been dated to be as old as 4.4 billion years!

3.8 Billion Years Ago  

Impacts Events Dramatically Reduced in Number
Asteroids continue to strike Earth and the other planets, but not as frequently.

3.8 Billion Years Ago  

Earliest Evidence Indicating Life (?)
Scientists are debating the fossil evidence and chemical signatures suggested as indicators of life at this time.

  Earliest Evidence Indication Life (?)
3.5 Billion Years Ago  

Volcanic Activity on the Moon
While the Moon has been geologically inactive for many millions of years, the youngest volcanic flows are about 1 billion years old.

~3.5 Billion Years Ago  

First Stable Continental Crust
In other words, things were calming down on Earth and stable land was forming.

3.5 Billion Years Ago  

Oxygen-"Rich" Atmosphere Begins to Develop
Photosynthetic organisms were pumping oxygen into the atmosphere.

3.0 Billion Years Ago   First Undisputed Fossils (Single-Celled Organisms)
The first organisms were prokaryotes (bacteria, photosynthesizing bacteria) — simple, single-celled organisms that do not have membrane-bound nucleus. The first fossils we find are stromatolites — pillar-like structures made of thin layers of sediment and photosynthetic cyanobacteria. Foreshadowing . . . Photosynthetic organisms add oxygen to our atmosphere.
3.0 Billion Years Ago  

Valles Marineris Begins Forming on MarsValles Marineris Begins Forming on Mars
The crust of Mars stretched and broke apart, creating a long, deep chasm — as long as the distance between California and New York!

3.0 Billion Years Ago   Earth's Moon Becomes Geologically Inactive
Okay, except for occasional volcanism . . .
2.8 Billion Years Ago  

Floods on Mars!
Water trapped beneath the martian surface as ice occasionally catastrophically melted and flooded across the surface, carving giant channels.

2.7 Billion Years Ago   First Eukaryotes
Single-celled organisms. Eukaryotes are more complex than prokaryotes and have a nucleus and membrane-bound organelles (mitochondria) . DNA is held within nucleus. Unlike prokaryotes, eukaryotes recombine DNA when they reproduce — there are many more opportunities for genetic diversity.
~2.5 Billion Years Ago   First Ice Age    
2.2 Billion Years Ago  

Significant Available O2 in Atmosphere
Oxygen had been building up via photosynthesizing organisms, but chemical processes used most of it.

2.2 Billion Years Ago  

Formation of Ozone Shield
As oxygen became more abundant in the atmosphere, some of it formed an ozone shield, protecting Earth's surface from harmful ultraviolet rays.

2.0 Billion Years Ago  

First Slime Molds
This is here solely because it is kind of cool to think about!

1.1 Billion Years Ago   Oldest Texas Rocks    
900 Million Years Ago  

Tallest Volcano in our Solar System Begins to FormOlympus Mons
Olympus Mons, 22 kilometers (14 miles) high, began forming. Some lava flows are so fresh that they might be younger than 1 million years. If Olympus Mons were on Earth, it would almost fill the entire state of Arizona.

700 Million Years Ago  

Supercontinent Rodinia Comes Together!
Okay, it took a long time for Rodinia to come together and pull apart again. Rodinia began forming about 1.9 billion years ago as the continents began to converge. By 600 million years ago, it had pulled apart.

~600 Million Years Ago  

Early Multicelled Critters
Ediacaran Fauna — funky-looking fossils found in Australia, China, Russia, Canada, and the United States. None had shells, so all we have are traces of these organisms with soft bodies. They look a bit like sea pens and jelly fish.

  Early Multicelled Critters
540 Million Years Ago  

First Shells
Shells — and other hard parts — offer protection and support to organisms. They also preserve far better than soft tissue, giving us a rich fossil record. Starting about 540 million years ago, lots of different shelled organisms are found as fossils.

525 Million Years Ago  

Earliest Chordates
Organisms with a notochord — a first step to a vertebra. A notochord is a stiff rod of dense tissue.

510 Million Years Ago  

First FishFirst Fish
The early fish did not have jaws or a vertebrae (they did have a notochord!). Many had plates covering all or part of their bodies. Some probably burrowed into the soft seafloor and dredged up their food.

430 Million Years Ago  

First Land Plants
There MAY be fossil spores from plants as early as ~500 million years ago. Think of “mosses” when you think of the first land plants — these early conquerors were low to the ground and needed access to water to reproduce. Only bacteria, slime, etc., were on land before this!

430 Million Years Ago  

First Insects
Not far behind the plants! Some fossil evidence for insects includes "bite" marks in plant fossils.

420 Million Years Ago  

First Vascular Plants
Vascular plants have a plumbing systems for transporting water and nutrients. Early vascular plants required water to reproduce (think ferns and horsetails).

410 Million Years Ago  

Once they made it onto land and developed an efficient piping system and strong tissue to support high growth, plants quickly grew taller, creating forests with multiple levels of growth.

400 Million Years Ago  

Whopping Big Lava Flows Cover the Surface of Venus
Unlike other terrestrial planets, much of the surface of Venus is not heavily cratered. It appears to have been covered and smoothed by lava flows between 300 and 500 million years ago.

370 Million Years Ago  

First Amphibians
There may be tracks at 390 million years ago, indicating earlier amphibians. The first amphibians probably lived in shallow, heavily vegetated waters. They evolved their “legs” to maneuver around all the vegetation. So legs came first, then the amphibians headed onto land. Amphibians are cold-blooded terrestrial animals that need to return to the water to reproduce (indeed, many must stay in moist environments so that they don't dry out). These first amphibians are the ancestors to our frogs and salamanders.

  First Amphibians
365 Million Years Ago  

First Gymnosperms (Seed-bearing Plants)
Gymnosperms don't need water for fertilization. They also invented the “pre-packaged” seed — self-contained with nutrients. This allowed the seed to stay dormant until conditions were right for sprouting. Seeds could be dispersed by organisms. The first gymnosperms were the ancestors of our pine trees, giant redwoods, and ginkos!

~310 Million
Years Ago

First Reptiles
Reptiles “invented” the self-contained egg, which includes all the things a developing embryo needs (nutrients, protection from drying out, shedding of waste). Unlike amphibians, which have to go back to water to lay their eggs, reptiles could live away from bodies of water. Reptiles are cold-blooded, terrestrial animals with skin that prevents them from drying out.

  First Reptiles
250 Million Years Ago  

90% of all Marine Species Become Extinct
Marine organisms, amphibians, and plants are hit hard by the largest mass extinction event known in Earth history. The cause is debated and may be related to multiple events, including volcanism, global climate change, and ocean overturn. This event may have cleared the playing field of competitors and aided the rise of the dinosaurs. There's always a winner in an extinction . . .

250 Million Years Ago  

Supercontinent Pangaea Assembled
All the continents came together (again!) to form one big land mass.

230 Million Years Ago  

First Dinosaurs
Could be as late as 220 million years ago. These reptiles started out as small carnivorous critters walking around on two legs (bipedal).

  First Dinosaurs
210 Million Years Ago  

First Mammals
+/– 30 million years; mammal features are challenging to identify in the fossil record. The first mammals were small, nocturnal critters. Early mammal fossils have some evidence of pits for whiskers and fur, suggesting another element of “mammal-ism” — that of being warm-blooded.

220 Million Years Ago  

First Birds ( Protoavis texensis ) (???)
Protoavis may actually be an early dinosaur, and not the first bird. It shares many characteristics with the early dinosaurs, but may also have had feathers.

200 Million Years Ago   Saturn Gets Its Rings (?)
Age is based on the rate at which the rings are spreading.
155 Million Years Ago  

First (Undisputed) Birds ( Archaeopteryx )
Most scientists believe that Archaeopteryx , a relative of the dinosaurs, is the ancestor of today's birds (so think of T-Rex the next time you see a sparrow . . .). Archaeopteryx has some reptile characteristics (teeth, long bony tail, grasping claws on its wing) and some bird characteristics (feathers; bird-like hip; thin, hollow bones). It probably was a weak flyer.

~100 Million
Years Ago

First Angiosperms (Flowering Plants)
Lots of debate on the timing of this event! Gymnosperms are commonly pollinated by wind; angiosperms have flowers that attract insects and birds, increasing the opportunities for pollination. Pollinated seeds are encased in nutrients — giving us the fruit we enjoy!

  First Angiosperms (Flowering Plants)
100 Million Years Ago   Tycho Crater Forms on the Moon
This is a clear, “fresh” (non-eroded) crater.
55 Million Years Ago   First Primates    
65 Million Years Ago  

Asteroid Smashes Into Earth; Extinction of Dinosaurs
And the winners are: The Mammals!

  Asteroid Smashes Into Earth; Extinction of Dinosaurs
55 Million Years Ago  

First Grasses
Grasslands became very widespread as our climate cooled in the last 45 million years.

~50 Million Years Ago   India Collides With Asia    
~45 Million Years Ago   Initial Uplift of the Himalayas    
~45 Million Years Ago   Most Recent Period of Global Cooling Begins    
~30 Million Years Ago  

Antarctic Ice Sheet Develops
Antarctica had separated from all other land masses. As global climate cooled, an ice sheet grew across the continent. The ice sheet is this old, but the actual ice is not ; the ice that makes up the ice sheet is constantly taken away by melting and as icebergs and renewed by falling snow.

5 Million Years Ago  

Mediterranean Ocean . . . the Whole Thing . . . Dries Out
Messinian Salinity Crisis — a layer of salt more than 2 kilometers (1.2 miles) thick is deposited in the Mediterranean.

~5 to 1.5 Million
Years Ago

Giant "Armadillos" Roam Gulf Coast of North America
Really. These critters were about 1.5 meters (5 feet) across.

5–10 Million
Years Ago

Uplift of the Colorado Plateau Initiated
The Grand Canyon is young geologically! As the Plateau rose, rivers cut down deeper and deeper, forming the canyon.

4 Million Years Ago  

First Early Hominid
Ardipithicus ramidus

2.5 Million Years Ago   Hominids Making and Using Tools    
~2 Million Years Ago  

Northern Hemisphere Ice Sheets First Form
The most recent period of glaciation is initiated.

500,000 Years Ago   First Human Use of Fire    
200,000–30,000 Years Ago   Neanderthals on the Scene    
150,000–200,000 Years Ago   Homo Sapiens First Appear    
3000 Years Ago  

Humans Creating Calendars, Planting Crops, and Navigating Based on Stars, Moon, and Sun

30–40 Years Ago   That's One Small Step for Man . . . One Giant Leap for Mankind
On July 20, 1969, Neil Armstrong was the first human to set foot on the lunar soil of our Moon.
  Boot print on the Moon

*Our understanding of the events that shaped our solar system changes constantly as new tools and new research expand and deepen our knowledge. New ideas undoubtedly will arise and replace the information above. The ages and events given do not always reflect the ongoing scientific debates, but rather reflect the broad consensus at this time.

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