2020-02-22_New_Scientist

8 | New Scientist | 22 February 2020

CHINA’s Wutai mountains may

contain the earliest fossil evidence

of an evolutionary milestone: the

moment that complex eukaryotic

life appeared on Earth.

Eukaryotes have large cells

with complex internal structures.

While the first eukaryotic

organisms were all single-celled,

they gave rise to all multicellular

life – including fungi, plants

and animals.

Leiming Yin at the Nanjing

Institute of Geology and

Palaeontology in China and his

colleagues found the fossils in

a set of rocks called the Hutuo

Group in the Wutai mountains.

Previous studies have shown

that the rocks were laid down

between 2.15 and 1.95 billion

years ago.

In total, the researchers found

eight kinds of microfossil: four are

bacteria, two couldn’t be identified

and two appear to be eukaryotes.

Of these two, one appears to

belong to a known genus of

eukaryotes called Dictyosphaera.

There were also six specimens

of a new genus that the team

has dubbed Dongyesphaera.

Both types of fossil have roughly

spherical cells with multilayered

outer walls and visible spines –

all features that the team says

suggests they are eukaryotes,

not bacteria (Precambrian

Research, doi.org/dmsf).

Experts contacted by

New Scientist gave the fossils a

cautious welcome.

It is plausible that they are

eukaryotes, says Małgorzata

Moczydłowska-Vidal at Uppsala

University in Sweden.“I could go

for them being eukaryotic,” says

Anette Högström at the Arctic

University of Norway in Tromsø.

However, the identification

is solely based on the shapes of

the fossils, says Yuangao Qu at

the Institute of Deep-sea Science

and Engineering at the Chinese

Academy of Sciences in Sanya.

“If more geochemical data

could be obtained, it would

be more convincing.”

If confirmed to be eukaryotes,

the fossils are arguably the oldest

known. Previously the oldest

confirmed eukaryotes were

around 1.5 billion years old.

Some researchers have claimed

to have found significantly older

eukaryotes: one 2017 study

reported fungi, which are

eukaryotes, in rocks 2.4 billion

years old. However, these older

microfossils are rare and poorly

preserved, and it isn’t clear that

they are really eukaryotes, says

Högström. They could be bacteria

that look superficially like fungi,

for instance.

If eukaryotes really were

present as early as 2 billion years

ago, they emerged in the wake of

tumultuous changes. The first

oxygen built up in the atmosphere

2.4 billion years ago, albeit at low

levels, in the Great Oxidation

Event. This was followed by an

ice age known as Snowball Earth.

These abrupt environmental

variations may have triggered the

evolution of eukaryotes, says Qu.

However, the mechanisms

of this are unclear, says

Moczydłowska-Vidal. She says

that the Great Oxidation Event

“might have triggered the

evolution of the first eukaryotes”,

but adds that this isn’t certain.

Meanwhile, it is even less clear

how the Snowball conditions

could have contributed, she says.

“The only certain thing is that

these microbes originated in

a marine environment with

relatively high oxygen levels

PR in the surface layers,” she says. ❚

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News

Particle physics

Antimatter looks like

matter – which is a

problem for physics

PHYSICISTS have made a key

measurement of anti-atoms, and

found that they look just like atoms.

The result means we are no closer

to solving the mystery of why we live

in a universe made only of matter,

or why there is anything at all.

Antimatter particles are the

same as matter particles, but

have the opposite electrical charge.

If the two meet, they annihilate

in a blitz of light and energy.

The problem is that the standard

model, physicists’ well-tested

theory of particles and their

interactions, predicts that matter

and antimatter were created in

equal quantities in the big bang,

so both should have disappeared in

an orgy of annihilation shortly after.

This has led to the suggestion

that there is a small imbalance

between matter and antimatter

properties, which allowed some

matter to survive and form the

universe of stars and galaxies we

live in. But we have failed to find

much evidence of one.

Now the ALPHA collaboration at

the CERN particle physics lab near

Geneva, Switzerland, has measured

a property known as the Lamb shift,

which is caused by fluctuations

in the quantum vacuum thought

to pervade all of space, in atoms

of antihydrogen.

These consist of a positively

charged electron, or positron,

circling an antiproton. Just as

the standard model predicts, the

Lamb shift was the same in atoms

of hydrogen and antihydrogen.

It is too early to conclude that the

Lamb shift can’t help to explain the

antimatter mystery, however. The

measurements are consistent only

to within one decimal place, so it

is possible that future research

will discover subtle differences

between the Lamb shift of atoms

and anti-atoms (Nature, DOI:

10.1038/s41586-020-2006-5).

“This measurement is certainly

an important step forward,” says

Chloé Malbrunot, who works on

the rival ASACUSA experiment,

also at CERN. ❚

Read an exclusive feature on the

mysteries of antimatter in next

week’s New Scientist

Richard Webb

Evolution

Michael Marshall

The oldest complex cells

Two-billion-year-old fossils may be world’s earliest eukaryotes

This Dictyosphaera

fossil may be one of the

earliest complex cells

“An imbalance between

matter and antimatter may

have allowed some matter

to survive the big bang”