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See ancient Earth from space

Earth during the Cambrian Period was relatively warm and without polar caps. Most of the continents resembled deserts and were clustered in the southern hemisphere. Life was small and simple mostly in the oceans. There were no land plants but fungi, algae, and lichens probably greened many land areas.

Over the past 750 million years, our blue marble has gone through remarkable changes — continents have shifted, ice ages have come and gone, sea levels have risen and fallen, and one-time deserts have turned green, allowing creatures to crawl out of the oceans and live off the land. 

These changes are now being made visible by the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. The first set of the Visible Paleo Earth visualizations are being released today, on Earth Day, and more will be available in coming weeks. 

"I think people looking at the whole period will realize how fragile our planet is, how it changes," Abel Mendez, who is leading the project, told me in advance of the public release.


Visualization contruction
Mendez constructed the visualizations by combing through color images of Earth from NASA's Next Generation Blue Marble project and blending them with the global paleoclimate reconstructions developed by Ronald Blakey from Northern Arizona University and Christopher Scotese from the University of Texas at Arlington.

University of Puerto Rico at Arecibo

The Americas 65 million years ago just before the extinction of dinosaurs after an impact in the Yucatan Peninsula (center). Our planet was warmer, had many more forests and almost no ice caps during the end of the Cretaceous Period.

As he built the visualizations, Mendez said he was struck by the fact that the distribution of land mass among the continents has changed dramatically over the past 750 million years, but the total land area has stayed consistent – between about 10 and 30 percent of total surface area. "I was expecting to see more," he said.

The color of the land area changes dramatically, especially beginning 500 million years ago, during an era known as the Cambrian Period. Life was small-sized back then, and mostly confined to the oceans. As a result, the continents were mostly deserts.

From that point forward, terrestrial life began to flourish. In the years leading up to the extinction of the dinosaurs, he noted, the planet was even greener than it is today. "That is something nice to see in the pictures," he told me. "Today we have too many deserts. The dinosaurs had more food."

Habitable exoplanets
In addition to providing Earthlings with a voyeuristic view of the changes through time on their own planet, Mendez's project is part of a larger goal to understand the habitability of Earthlike planets around other stars.

Today, very few exoplanets can be directly imaged, but that will change in coming years. Mendez hopes to learn how the light reflected by faraway terrestrial planets changes can vary, depending on how much ice or vegetation covers their landscapes.

"If we can see that light, we will be able to have an idea of the continental distribution and how much vegetation" the planets have, Mendez said.

For today, the focus is on our planet. These visualizations provide a view of Earth's ever-changing continents and climate from the past to the present. What's in store for the future? "There are people who have some ideas of how the planet will be in the future with climate and continental change," Mendez said. "Eventually, I will make images for those also."

More about Earth's past, present and future:


John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).