These “methanogens” could have helped regulate the early Earth’s climate by providing greenhouse gases, helping to prevent freezing conditions that would have stifled the fragile development of life on Earth.

Methane comes from three sources: through the thermal decomposition of organic material; from non-biological reactions of simple inorganic compounds; or through metabolic activity of methanogenic microbes. Each leaves a different carbon isotope signature.

Until now, no geological evidence for methanogens had been found in the Early Archaean era that represents the first 1.5 billion years of Earth’s 4.5-billion-year history. But a team led by geologist Yuichiro Ueno of Tokyo Institute of Technology, Yokohama, has found the depleted carbon 13 isotope signature produced by modern methanogens in 3.46-billion-year-old rocks.

Trapped bubbles

The researchers examined hydrothermal dykes – sheets of precipitated minerals intruded into rock by the flow of hydrothermal water – in the Pilbara craton in Western Australia.

The Pilbara rocks represent some of the few vestiges of Archaean continents, known as cratons, which still exist relatively unchanged by geological processes. The carbon samples were preserved in tiny bubbles of fluid trapped in the minerals.

“This study supports conjectures that methanogenesis was one, if not the, primordial form of metabolism powering the earliest organisms on Earth,” says Roger Buick at the University of Washington in Seattle, US, a specialist in the origin of life on Earth. The finding boosts the idea that “methane was an important greenhouse gas at a time when the Sun was much less bright than it is today.”

Journal reference:

South American glyptodonts, relatives of armadillos, became extinct about 10
000 years ago. Their protective armour weighed up to 400 kilograms, about the
weight of five men, and it probably served as a tortoise-like hideaway from
giant carnivorous birds and sabre-toothed mammals. However, research by McNeill
Alexander at the University of Leeds and his colleagues suggests that the
formidable carapace was also used as a shield in fights between
glyptodonts—and that tails were powerful weapons.

Glyptodonts had broad, muscular tails protected by tough plates. In some
species, these fused into mace-like clubs at the tip. Like deer antlers, they
were probably used not against predators but rather to fight each other, perhaps
over mates or territory. “It suggests that glyptodont design has a lot to do
with sex and violence,” says Alexander.

His team performed biomechanical tests to see if the tail was up to the task
of seriously damaging an opponent. Drawing from previous work on smashing human
and goat skulls, and after scaling up the forces, Alexander calculated that the
tail would need between 1400 and 6000 joules to crack the carapace. Then, using
a cast of a fossil tail cone, the team estimated the muscle mass controlling
each side of the tail and how much energy would be needed to move it in a rapid
tail snap—about 3000 joules. So the tail could have done the damage.

Luckily for the glyptodonts, they may also have evolved an internal “boxing
glove” to absorb the blows. Alexander says a cavity between the carapace and the
vertebral column may have contained a fatty cushioning pad that served as an
energy absorber in battle.