Ancient Earth, Alien Earth

Sphere Demo

©2018Pacific Science Center

Script by Dave Cuomo, Pacific Science Center

Science Advisors:
Dr. Erika Harnett, University of Washington,
Dr. Giada Arney, University of Washington

This script is based upon work supported by NASA Astrobiology Institute under Cooperative Agreement No. NNA13AA93A. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.

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  • If these materials or a portion of these materials are copied as is, please credit as follows: “Ancient Earth, Alien Earth demonstration created by Pacific Science Center, NASA Astrobiology Institute under Cooperative Agreement No. NNA13AA93A.”
  • If new activities are created that are based on this original activity, please credit as follows: "Activity modified from Pale Blue Dot demonstration created by Pacific Science Center, NASA Astrobiology Institute under Cooperative Agreement No. NNA13AA93A.”


Ancient Earth, Alien Earth is a live, 20 minute demo, featuring Science on a Sphere, a dynamic interactive data modeling tool. In this show, our guests will explore the different ways Earth has appeared in the past. Using these ancient, alien Earths as an analog we then explore different places in the solar system which while quite different than the Earth of today are quite similar to the Earth of the past. He guests will gain an understanding that an “Earthlike” planet might be quite different from the Earth as seen today.

Props and Materials

  • I-Pad
  • Science on a Sphere


  • Milky Way (used as background to show attract).
  • Blue Marble & Nighttime Lights
  • Blakey Paleo Earth
  • Hadean Earth (PSC Made Global Mosaic)
  • Titan Earth (PSC Made Global Mosaic)
  • Titan Colorized
  • Titan B&W
  • Stromatolites 1 PIP
  • Stromatolites 2 PIP
  • Cyanobacteria PIP
  • Snowball Earth (PSC Made Global Mosaic)
  • Villarrica Eruption PIP
  • Cambrian PIP
  • Blakey Paleo Earth
  • Kepler Space Telescope PIP
  • Snowball Earth (PSC Made Global Mosaic)
  • Europa
  • Deep Sea Vent (Black Smoker) PIP
  • Milky Way (Background for A. C. Clark Quote)
  • Blue Marble and Nighttime Lights

What you say / What is Displayed
Hey Everyone!
Today we are going to compare some planets and other astronomical bodies. We are going to compare them with a planet we all know very well. In fact a great image of it is right behind me on Science on a Sphere, what planet am I talking about? That’s right Earth. We are looking at a picture Earth from space. That is what it would actually look like to your eyes.
Who would like to help me learn from this image?
Allright, What’s your name?
Say hi Everyone!
Let me ask you what do you think the blue stuff around here is?
That’s right it is water. This white stuff? Yes, clouds. Now how about the green. Yes vegetation.
Do you know the name of this continent? I’ll help you, it starts with an A. Africa that is right. And This one? South America.
Let’s have some applause for our volunteer.
I’m going to ask you all a question, has the Earth always looked like this? /
Blue Marble
No not at all. In fact if someone were to see the Earth just 120 million years ago it would be different. Look Africa and South America are joined together. In fact we now know the continents are always moving and shifting, reshaping the surface.
But there are still identifiable features. We can still see water and land. But what if we could see Earth even further in the past. Could we recognize it as Earth?
Are you ready to take a trip a long, long time ago? / Plate Tectonics

What do we see here? This is an artist’s illustration of what the Earth might have looked like over 4 billion years ago. What do you think we are looking at? That’s right, lava. Scientists think that long ago the Earth, and everything in the solar system was being constantly being bombarded by meteorites. This caused the surface to heat up and melt.
Do you think life could have existed here?
No probably not, but we do know that life eventually evolved on Earth, even though Earth started out very inhospitable to life.
That’s why it is important to understand the different reasons a planet might appear like this image of Earth. By the way this period in Earth’s history is called the Hadean. Named after Hades the underworld of Greek mythology. In a way it is “Hell like.”
The planets first formed from collisions with smaller bodies. The objects would collide and merge both getting bigger and getting hotter and sometimes throwing molten rock into space to form another object.
Evidence in some of the rocks brought back by Apollo Astronauts suggests the Moon formed from such a collision.
So does this image represent an “Earthlike” planet? Yes it does but, remember, not the Earth of today but an Earth from long ago before there was life.
Now, evidence shows that the Earth formed around 4.5 Billion years ago and the first life on Earth appeared around 3.7 Billion years ago. So Earth must have changed. It stopped being molten. / Hadean Earth
As the Earth cooled down, water, from comets and also from chemical processes in the interior, covered the globe. The atmosphere would have been mostly Nitrogen, but also would have contained Carbon Dioxide, Ammonia, and Methane. We’re still not sure how thick this atmosphere might have been. Recent studies have suggested it was much thinner than previously thought, perhaps thinner than today’s atmosphere. In either case the atmosphere was filled with greenhouse gases which trapped the heat and kept the Earth very warm. Also the Methane would have reacted with the light from the sun to form long chains of Hydrocarbons. Today we call hydrocarbons in the atmosphere smog. The early Earth could have been covered with smog. Smog is bad for life on Earth today, but it might have been helpful to life early on by acting like a planetary sunscreen layer, blocking a type of damaging light called ultraviolet. Chemical reactions that form the smog might also have produced key ingredients for life like the building blocks of proteins.
The Carbon in the Methane, and the water are two of the key ingredients for the development of life.
Now does this look Earthlike to you? No but it is Earth, though a very Alien Earth to us.
The thing is we know of a place like this it’s not orbiting a distant star, it is much closer. It’s Saturn’s Moon Titan. / Titan Earth
Here is Titan, the cloud tops would look like a fuzzy Orange Tennis Ball. The Orange is caused by the Hydrocarbons in the atmosphere.
How many of you have heard of the following thing happening: A liquid pools up on the surface, it evaporates into the atmosphere where it condenses to form clouds. It them precipitates, or rains back down to the surface. What am I talking about?
Yes the Water Cycle. We know of only two places where this happens, here on Earth of course but also on Saturn’s Moon Titan. But on Titan it’s not water, it’s Methane! This is a lake of liquid Methane. These clouds are made of Methane.
One of the key requirements for life is carbon based chemistry. You are looking at Carbon based chemistry in action.
What if we could go back and peer through the clouds of that fuzzy Orange Ball Earth. / Titan

Here is the Orange smog of hydrocarbons, what’s this blue stuff underneath?
Yes! Water. Hydrocarbons and water the ingredients for life. And life did form on this planet because this is Earth. It formed 3.8 billion years ago and we have evidence today of that life in fossils. / Hydrocarbon Earth
Here is a picture of one of these fossils. It’s called a stromatolite. It’s a type of algae called cyanobacteria that is the earliest life on Earth.
Today these ancient fossils are found in Western Australia. The life forms that left these fossil traces were types of blue-green algae. These microscopic plants take Carbon Dioxide out of the atmosphere and release Oxygen into it.
Some research suggests these first lifeforms changed the Earth’s atmosphere, decreasing the amount of CO2 and increasing the amount of Oxygen.
/ Stromatolite PIP
Hey did you know that life could change a planet? It can. Everyone take a deep breath. Now exhale.
When we breathe in what are we getting? Oxygen and when we exhale? Carbon Dioxide.
Did you know plants do the opposite? Yes, plants breathe in Carbon Dioxide and breathe out Oxygen.
Some of the first life on Earth released Oxygen into the atmosphere and took Carbon Dioxide out of it. Now Carbon Dioxide is a greenhouse gas. It traps heat near the surface of a planet. Now a little greenhouse effect is a good thing. On the Moon with no atmosphere and no greenhouse effect at night it’s over 200 degrees below zero Fahrenheit.
Well the cyanobacteria increased the Oxygen content of the atmosphere and changed the Earth’s atmospheric chemistry. This could have helped trigger a snowball Earth.
With less Carbon Dioxide in the atmosphere the planet started to cool down.
There is some evidence that suggests the entire Earth froze over.
Here is an artist illustration of what that Earth might have looked like.
Life exists on this Earth but it is isolated in small pockets.
A puddle of life in one place would have little contact with another puddle of life. Each little pocket would go through its own adaptations for its own unique environment. / Snowball Earth
Eventually the planet warmed back up. Volcanoes would have spewed CO2 back into the atmosphere. Warming the planet up, and melting the ice. / Volcano (PIP)
The little pockets of life would expand. All of the diversity from each pocket would accelerate change. Very quickly, at least quickly in geologic time. Over the next 30 million years life rapidly spread over the Earth, increasing in diversity. During this time all the major phyla we have today emerged. / Cambrian Explosion PIP
This brings us back to where we started. Here’s an image of plate tectonics. We can start out about 500 million years ago, during the Cambrian and watch the plates move until they get to their current position. / Continental Drift
Scientists called Astrobiologists are currently looking for Earthlike planets, using instruments like this Space Telescope called Kepler.
But as we’ve seen “Earthlike” can have multiple meanings depending on when in Earth’s history we are talking.
Let’s talk a look. / Kepler ST (PIP)
Here’s Snowball Earth again. This is an example of what Earth actually looked like in the past.
Scientists are trying to determine if they could identify a world like Snowball Earth if we find it orbiting a distant star.
So let’s say we found a planet like this artist’s drawing, an icy world with Oxygen in the atmosphere. Might it be Earthlike?
Maybe! / Snowball Earth
Now here is an icy world that Astrobiologists are very interested in and it’s in our own Solar System.
Europa is a moon of Jupiter and it’s what scientists call an icy body. The surface of this moon is frozen water. And that the water ice crust is covering liquid water.
Let’s take a look at this area called Conamara Chaos.
It looks as though the ice has broken up, floated free, refrozen and then broken up again. Over and over. It’s as though there is some type of internal heating taking place. What could cause that?
We don’t know but on Earth one thing that could cause this are hydrothermal vents.
/ Europa
Here is hot water, heated by the Earth’s interior rising from the sea floor. Here on Earth areas like this are teeming with diverse lifeforms.
Might there be colonies of microscopic organisms under the ice on Europa? We don’t know. But we are very interested in finding out. / Image of a Vent
A famous author and scientist, Arthur C. Clark, once said. “Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering.”
Is it out there? We don’t know.
Here is Earth again, as it looks today. Everyone you’ve ever known, everyone who ever was has lived here.
Scientists are looking.
And that is Alien Earth. Thank you for coming, I’d be happy to answer any questions you might have. / Blue Marble