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70

January/February 2018^ DISCOVER^71

TOP: MATTHEW DODD. BOTTOM: MARK GARLICK/SCIENCE SOURCE

❯

AS A FAINT, YOUNG SUN

shone on our freshly formed

Earth around 4 billion years

ago, primitive creatures, each less

than half the width of a human

hair, were thriving around volcanic

vents.

That’s the conclusion of an

international team of geoscientists

who announced in March

in Nature they’d unearthed

these creatures’ remains.

The microfossils, potentially the

oldest discovered, were locked

inside rocks in remote northern

Canada that were 3.8 billion to

4.3 billion years old — roughly

when scientists think life started.

But that wasn’t the only finding

this year that suggested life on

Earth is older than we thought. In

September, Japanese geoscientists,

publishing in Nature, said they’d

also found traces of 3.95 billion-

year-old life-forms in different

northern Canadian rocks.

Some critics doubt the age

claims of both studies and say

the samples need more rigorous

testing before anything can be

confirmed. But the findings fit an

emerging consensus that life began

around 4 billion years ago, a

period when comets and asteroids

bombarded Earth.

Until relatively recently,

scientists thought such impacts

would’ve sterilized our world until

roughly 3.8 billion years ago. But

new evidence is suggesting those

craters helped create hydrothermal

vents that set the stage for life

to emerge.

“This makes life appear to be

a relatively easy process to kick-

start on the planet,” says Matthew

Dodd of University College

London and lead author on the

March paper. — ERIC BETZ

When Did

Life Appear?

Tiny tubes of the mineral hematite, found

around hydrothermal vent deposits,

might be the oldest microfossils on Earth

and evidence for when life on our planet

came to be.

A glimpse of what our primitive

planet might have looked like

when it was forming, more than

4 billion years ago.