Life Could Have Survived Earth's Early Pounding

Image: A new study suggests that heat-loving microbes living more than 300 m underground could have survived a massive barrage of impacts 3.9 billion years ago (Image: Don Davis)

From New Scientist:

Microbes living deep underground could have survived the massive barrage of impacts that blasted the Earth 3.9 billion years ago, according to a new analysis. That means that today's life might be descended from microbes that arose as far back as 4.4 billion years ago, when the oceans formed.

Around 3.9 billion years ago, shifts in the orbits of the gas giant planets are thought to have disrupted other objects in the solar system, sending many hurtling into the inner planets. Geologists call that time the Hadean Eon, and thought its fiery hell of impacts would have sterilised the Earth.

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Oldest Fossil Evidence for Animals Found

Hymeniacidon sp. Photograph: Jane Fromont, WA Museum

From Live Science:

The oldest fossilized evidence of animals has been unearthed in Oman and reveals that tiny sea sponges were abundant 635 million years ago, long before most of the planet's other major animal groups evolved, according to a new analysis.

This early life hardly looked like us, but some of the so-called demosponges can be sizable today. Demosponges still make up 90 percent of all sponges on Earth and 100 percent of Earth's largest sponges, including barrel sponges, which can be larger than an old-style phone booth.

The ancient demosponges — probably measuring across no more than the width of a fork tine — were pinned down via fossilized steroids, called steranes, which are characteristic of the cell membranes of the sponges, rather than via direct fossils of the sponges themselves.

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