A Special Planet

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Floor 1

Of all the objects in our solar system, only Earth can support life as we know it. It is the right size, and the right distance from the Sun. Its temperature range is such that its free water is present and available for life. And the Earth’s climate has been stable for billions of years, a factor in allowing life to emerge, flourish, and evolve. How life began, how it evolved, and how it affected the evolution of the planet itself, are among the great questions of our time.

How Did Life Begin?

One of the simplest definitions of a life-form is: anything with the capacity to reproduce and regulate itself. Before life began, the complex organic, or hydrocarbon-bearing, molecules that make up RNA and DNA, the building blocks of life, must have formed. No one knows exactly how, but many ideas have been put forward.

This download explains more about the evolution of our atmosphere and its impact on life on Earth.

In This Section

Stromatolites

Stromatolites — mats of bacteria that trap and precipitate sediments — were rare in the early Precambrian era, but they became more common 2.6 billion years ago, when shallow seas were more extensive. Because the atmosphere during much of the Precambrian had little oxygen, there was no protective ozone layer, and life could prosper only in water of just the right depth — shallow enough for sunlight to penetrate, but deep enough to block out the Sun’s harmful ultraviolet radiation.

A close-up view of a stromatolite boulder in the field in the desert — the Atlantic coast appears far in the background.
photo credit: Craig Chesek, © American Museum of Natural History

This view shows some examples of the Mauritanian desert's flora and fauna.
photo credit: Craig Chesek, © American Museum of Natural History

Ed Mathez with colleagues Heather Sloan and Alexis Mossine-Pouchkine, a professor from the University of Montpellier, examine boulders of 900 million year-old stromatolite.
photo credit: Craig Chesek, © American Museum of Natural History

Janine Sarfati, a stromatolite expert from the University of Montpellier, wears a traditional Saharan head piece, or shehsheh to shield her from the sun.
photo credit: Craig Chesek© American Museum of Natural History

The boulder of Mauritanian stromatolite 'hangs out' at the Connecticut quarry, waiting to be measured and weighed for incorporation into the Museum's exhibit.
photo credit: Craig Chesek © American Museum of Natural History

AMNH/R.Mickens

How do we know about the early atmosphere?

Among the oldest rocks on Earth are many sedimentary rocks known as banded iron formations. They formed in an atmosphere and ocean containing little or no free oxygen.