Question

stromatolites Two-page report

geology

© Kerri Lathrop 200-5

Answer 1

•Stromatolites

The Stromatolites of Hamelin Pool at Hamelin Station Reserve may look like a cross between gigantic cauliflowers and rocks, but they're incredibly important as modern examples of the earliest known life forms on Earth.

Stromatolites – Greek for ‘layered rock’ – are microbial reefs created by cyanobacteria (formerly known as blue-green algae).

Stromatolite deposits are formed by sediment trapping and binding, and/or by precipitation activities of the microbial communities . The microbes are active on the surface layer of the Stromatolites, while the underlying build-up is a lithified remnant of former microbial surface communities, that could be interpreted as a trace-fossil.

These deposits built up very slowly: a single 1m structure may be 2,000 to 3,000 years old. But the tiny microbes that make up modern Stromatolites are similar to organism that existed 3.5 billion years ago!

For context, consider that the Earth itself has been around for 4.5 billion years, and that Homo sapiens have only been on Earth for 195,000 years.

What’s more, Stromatolites are the reason why we’re alive today! Before cyanobacteria the air was only 1% oxygen. Then, for 2 billion years, our photosynthesising Stromatolites pumped oxygen into the oceans (like underwater trees, before trees existed). When the oceans’ waters were saturated, oxygen was released into the air, and with around 20% of oxygen in the air, life was able to flourish and evolve.

Even today you can see Stromatolites ‘fizzing’ underwater, releasing oxygen.

Stromatolites are layered mounds, columns, and sheet-like sedimentary rocks. They were originally formed by the growth of layer upon layer of cyanobacteria, a single-celled photosynthesizing microbe that lives today in a wide range of environments ranging from the shallow shelf to lakes, rivers, and even soils. Cyanobacteria are prokaryotic cells (the simplest form of modern carbon-based life) in that they lack a DNA-packaging nucleus. Bacteria, including the photosynthetic cyanobacteria, were the only form of life on Earth for the first 2 billion years that life existed on Earth.

Shows internal layering and close-up of lamina structure. Surface is covered by a felt of cyanobacterial filaments that trap sediment grains that are washed across the mat surface. Abundant sediment supply produces granular laminae, low sediment supply produces layers rich in organic matter.

•Where do Stromatolites live?

Living Stromatolites are no longer widely distributed. There are only two well-developed marine Stromatolite areas in the world: in the Bahamas and at Hamelin Pool in the Shark Bay area of Western Australia. Hamelin Pool is home to the most extensive living Stromatolite system in the world: the organisms thrive in the area’s hypersaline water, which is twice as salty as normal seawater.

•Threats to Stromatolites

Hamelin Pool is perfect for Stromatolites because it’s hypersaline. Sea grass forms a ‘barrier’ between Hamelin Pool and the rest of the ocean, preventing ocean circulation, which would dilute the super-salty water.

But sea grass meadows are being damaged by the runoff caused by floods and extreme temperature events. Climate change is likely to lead to more frequent tropical storms and more frequent flooding events in the area,threatening the Stromatolites of Hamelin Pool.

Human interference is another threat. To protect the delicate structures, visitors are restricted to the boardwalk.